Evaluation of Alternatives for the Lake Okeechobee Sediment Management Feasibility Study C-11650

Transcription

1 Evaluation of Alternatives for the Lake Okeechobee Sediment Management Feasibility Study C April 2003

2 R EPORT Evaluation of Alternatives Lake Okeechobee Sediment Management Feasibility Study C South Florida Water Management District West Palm Beach, Florida April 2003

3 Table of Contents ACRONYMS AND ABBREVIATIONS EXECUTIVE SUMMARY... ES-1 1. INTRODUCTION BACKGROUND PURPOSE OF THE FEASIBILITY STUDY REGULATORY DRIVERS FEASIBILITY STUDY PROCESS FOR MORE INFORMATION APPROACH TO EVALUATION OF ALTERNATIVES OVERALL APPROACH Modeling Public and Interagency Outreach Data Collection and Review Sediment Characterization Internal Loading Evaluation Socioeconomic Evaluation Case Study Reviews Cost Estimating EVALUATION PROCESS ALTERNATIVE 1 NO IN-LAKE ACTION DETAILED DESCRIPTION NO IN-LAKE ACTION EVALUATION METHOD Pelagic (Open-water) Zone Effects on the Near-Shore Region UNCERTAINTY IMPACTS AND ISSUES RESULTS OF EVALUATION NO IN-LAKE ACTION Pelagic Zone Near-Shore Region Goal 1: Maximize Water Quality Improvements PM 1A: Minimize Time to Achieve Phosphorus Target PM 1B: Maximize Reductions in Water Column Phosphorus Concentrations PM 1C: Maximize TSS Reductions in the Short Term and the Long Term PM 1D: Minimize Algal Blooms PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and the Long Term PM 1F: Minimize Downstream Impacts Goal 2: Maximize Engineering Feasibility and Implementability Goal 3: Maximize Cost-Effectiveness PM 3A: Minimize Construction Costs PM 3B: Minimize Operation and Maintenance Costs PM 3C: Maximize Benefits (Material Reuse) Goal 4: Maximize Environmental Benefits PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone PM 4B: Maximize Benefits to SAV PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities PM 4D: Minimize Negative Impacts to the Manatee PM 4E: Minimize Negative Impacts to the Alligator PM 4F: Minimize Negative Impacts to the Okeechobee Gourd PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds Goal 5: Maximize Socioeconomic Benefits /10/2003 engineers & scientists TOC-1

4 PM 5A: Maximize Regional Socioeconomic Benefits PM 5B: Minimize Environmental/Social Inequities PM 5C: Maximize Community Acceptance PM 5D: No Impacts on Water Supply or Lake Operations ALTERNATIVE 2 CHEMICAL TREATMENT DETAILED DESCRIPTION CHEMICAL TREATMENT Methodology (Dose, Application, and Equipment) Shipment and Transport of Materials to the Site Land-use Needs (Staging of Equipment and Materials, and Production Facility) Duration of Alternative (Staging, Implementation, Post-Implementation) Staging Implementation Post-Implementation Data Needs Summary EVALUATION METHOD ILPM Model Simulations LOWQM Simulations UNCERTAINTY IMPACTS AND ISSUES RESULTS OF EVALUATION CHEMICAL TREATMENT Goal 1: Maximize Water Quality Improvements PM 1A: Minimize Time to Achieve Phosphorus Target PM 1B: Maximize Reductions in Water Column Phosphorus Concentrations PM 1C: Maximize TSS Reductions in the Short Term and Long Term PM 1D: Minimize Algal Blooms PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and Long Term PM 1F: Minimize Downstream Impacts Goal 2: Maximize Engineering Feasibility and Implementability PM 2A: Maximize Technical Reliability PM 2B: Maximize Technical Scalability PM 2C: Maximize Equipment and Material Availability PM 2D: Maximize Permanence PM 2E: Minimize On-Shore Land Use Needs and Conflicts Satisfy Permitting Requirements Goal 3: Maximize Cost Effectiveness PM 3A: Minimize Construction Costs PM 3B: Minimize Operation and Maintenance Costs PM 3C: Maximize Benefits (Material Reuse) Goal 4: Maximize Environmental Benefits PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone PM 4B: Maximize Benefits to Submerged Aquatic Vegetation PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities PM 4D: Minimize Negative Impacts to the Manatee PM 4E: Minimize Negative Impacts to the Alligator PM 4F: Minimize Negative Impacts to the Okeechobee Gourd PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds Goal 5: Maximize Socioeconomic Benefits PM 5A: Maximize Regional Socioeconomic Benefits PM 5B: Minimize Environmental/Social Inequities PM 5C: Maximize Community Acceptance PM 5D: No Impacts on Water Supply or Lake Operations ALTERNATIVE 3 DREDGING WITH CONFINED DISPOSAL FACILITY FINAL ALTERNATIVE DEVELOPMENT DETAILED DESCRIPTION DREDGING WITH CONFINED DISPOSAL FACILITY (CDF) General Assumptions for Dredging with CDF Alternatives Target Area /10/2003 engineers & scientists TOC-2

5 Sediment Characterization Dredging Approach Dredged Material Transportation CDF Construction Water Treatment Dredging Timeframe Overall Timeframe Land-Use Needs Resources Fugitive Short-Term Phosphorus and Solids Release During Dredging Effectiveness Modeling Uncertainty Impacts and Issues Model Simulations for Dredged Material Management Options Input File Changes Post-Processing Results RESULTS OF EVALUATION DREDGING Goal 1: Maximize Water-Quality Improvements PM 1A: Minimize Time to Achieve Phosphorus Target PM 1B: Maximize Reductions in Water-Column Phosphorus Concentrations PM 1C: Maximize Total Suspended Solids (TSS) Reductions in the Short Term and the Long Term PM 1D: Minimize Algal Blooms PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and the Long Term PM 1F: Minimize Downstream Impacts Goal 2: Maximize Engineering Feasibility and Implementability PM 2A: Maximize Technical Reliability PM 2B: Maximize Technical Scalability PM 2C: Maximize Equipment and Material Availability PM 2D: Maximize Permanence PM 2E: Minimize On-Shore Land-Use Needs and Conflicts PM 2F: Satisfy Permitting Requirements Goal 3: Maximize Cost-Effectiveness PM 3A: Minimize Construction Costs PM 3B: Minimize Operation and Maintenance Costs PM 3C: Maximize Benefits (Material Reuse) Goal 4: Maximize Environmental Benefits PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone PM 4B: Maximize Benefits to Submerged Aquatic Vegetation (SAV) PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities PM 4D: Minimize Negative Impacts to the Manatee PM 4E: Minimize Negative Impacts to the Alligator PM 4F: Minimize Negative Impacts to the Okeechobee Gourd PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds Goal 5: Maximize Socioeconomic Benefits PM 5A: Maximize Regional Socioeconomic Benefits PM 5B: Minimize Environmental/Social Inequities PM 5C: Maximize Community Acceptance PM 5D: No Impacts on Water Supply or Lake Operations SUMMARY AND RECOMMENDATIONS SUMMARY RECOMMENDATIONS REFERENCES /10/2003 engineers & scientists TOC-3

6 Tables 3-1 Nutrient and TSS Concentrations in LOWQM No In-Lake Action Alternative Scenario 3-2 Loading Rates in Metric Tonnes per Year 3-3 Summary of Initial Conditions for Key Parameters Used in the LOWQM Model 3-4 Sediment Bulk Density for Different Sediment Types 4-1 Conceptual Cost Estimate Alternative 2 Chemical Treatment Summary Estimate 5-1 Properties of Mud Zone Sediment 5-2 Average Daily and Maximum Daily TSS Concentrations 5-3 Conceptual Cost Estimate Alternative 3A Hydraulic Dredging to Two Island CDFs Summary Estimate 5-4 Conceptual Cost Estimate Alternative 3B Hydraulic Dredging to Shoreline CDF Summary Estimate 5-5 Conceptual Cost Estimate Alternative 3C Hydraulic Dredging to Upland CDF Summary Estimate 6-1 Summary of Performance Measure Scores for No In-Lake Action, Chemical Treatment, and Dredging Alternatives Figures 1-1 Lake Okeechobee and Surrounding Areas 1-2 Lake Okeechobee Site Map 1-3 Total Phosphorus Content in Surficial Sediments Habitat Regions & Spatial Distribution of Sediment Types 2-1 Phosphorus Concentration by Depth in Lake Okeechobee Mud Layer 2-2 Simplified Diagram Illustrating Major Processes and Transport Pathways Involved in Internal Loading of Phosphorus in Shallow Lakes 3-1 Projected Decline in Input TP No In-Lake Action 3-2 Annual Average Lake Stage Assumed in Model Simulations 3-3 Predicted Annual Frequency of Algal Bloom Events 3-4 Short-Term Variations in TSS and SAV 3-5 Particulate Phosphorus vs. TSS for Pelagic Stations 1972 to Estimated Contribution of Algal and Consolidated Resuspension to Particulate P 3-7 Predicted TP Concentrations for Long-Term Simulations Model Comparison 3-8 Lake TP Concentrations as a Function of Inflow TP Concentrations Model Comparison 3-9 Response Time of Lakewater TP Concentrations to Reduction in Inflow TP Concentrations 3-10 Sensitivity Analysis Results and Effect of Uncertainty in Exchange Depth (z) 3-11 Predicted Long-Term TP Dynamics ILPM Results No In-Lake Action Alternative 3-12 Predicted Long-Term TP Dynamics LOWQM Results No In-Lake Action Alternative 3-13 Time Series Comparison ILPM vs. LOWQM No In-Lake Action Alternative 3-14 Average Particulate P in Near-Shore Region from Sediment Resuspension (LOHTM) 4-1 Alum Binding Coefficient as a Function of Surface Inflow TP Concentration 4-2 Effective Alum Coefficient in ILPM Model 4-3 ILPM Comparison No In-Lake Action vs. Chemical Treatment 4-4 LOWQM Comparison No In-Lake Action vs. Chemical Treatment 4-5 Predicted TP Concentrations for Chemical Treatment ILPM vs. LOWQM 4-6 TP Concentration Comparison No Treatment, Single Treatment, Multiple Treatments 4-7 Annual Algal Bloom Frequency No In-Lake Action vs. Chemical Treatment (ILPM) 4-8 Annual Algal Bloom Frequency No In-Lake Action vs. Chemical Treatment (LOWQM) 4-9 Annual Algal Bloom Frequency Chemical Treatment (ILPM vs. LOWQM) 4-10 Cumulative Frequency Distribution Algal Bloom Probability (ILPM) 4-11 Cumulative Frequency Distribution Algal Bloom Probability (LOWQM) 4/10/2003 engineers & scientists TOC-4

7 4-12 Cumulative Frequency Distribution Algal Bloom Probability (ILPM vs. LOWQM) 5-1 Alternative 3A 5-2 Alternative 3B 5-3 Alternative 3C 5-4 Sediment Removal Schedule 5-5 ILPM Predicted TP Concentrations Dredging vs. No In-Lake Action 5-6 LOWQM Predicted TP Concentrations Dredging vs. No In-Lake Action 5-7 ILPM Uncertainty in Sediment TP Concentrations Dredging Scenario 5-8 ILPM Uncertainty in Lakewater TP Concentrations Dredging Scenario 5-9 LOWQM and ILPM Comparison Dredging Alternative 5-10 ILPM Predicted TP Concentration in Lakewater 5-11 ILPM Predicted Lakewater TP Dredging vs. No Dredging 5-12 Predicted TSS Concentrations Three Dredging Scenarios 5-13 Comparison of TP Concentrations in Residual Sediment 5-14 ILPM Comparison of TP in Pelagic and Near-Shore Zones 5-15 LOWQM Comparison of TP in Pelagic and Near-Shore Zones 5-16 Near-Shore TSS Comparison 5-17 Near-Shore Particulate P Comparison No In-Lake Action vs. Dredging 5-18 SAV Biomass Comparison No In-Lake Action vs. Dredging 5-19 ILPM Algal Bloom Frequency Comparison No In-Lake Action vs. Dredging 5-20 LOWQM Algal Bloom Frequency Comparison No In-Lake Action vs. Dredging 5-21 TN:TP Comparison No In-Lake Action vs. Dredging 5-22 Cumulative Frequency Distribution of Algal Bloom Occurrence in Near-Shore Zone No In-Lake Action vs. Dredging 6-1 Relative Comparison of Alternative Performance 4/10/2003 engineers & scientists TOC-5

8 Acronym and Abbreviation List 137 Cs Cesium Am Americium-241 Al aluminum Al(OH)3 aluminum hydroxide Al-P aluminum-bound phosphorus alum aluminum sulfate BBL Blasland, Bouck & Lee, Inc. BMP Best Management Practice CDF confined disposal facility CERP Comprehensive Everglades Restoration Program cm centimeters cm 3 cubic centimeters CTLs Cleanup Target Levels cy cubic yards District South Florida Water Management District DOR Department of Revenue e.g. (lat.) exempli gratia for example EA EA Engineering, Science, & Technology, Inc. EFDC Environmental Fluid Dynamics Code EIS Environmental Impact Statement ERP Joint Environmental Resource Permit et al. (lat.) et alia and others FAC Florida Administrative Code FDACS Florida Department of Agricultural and Consumer Services FDEP Florida Department of Environmental Protection FS Feasibility Study FWC Florida Fish and Freshwater Conservation Commission Fe iron ft feet g grams g/cm 3 grams per cubic centimeter g/m 2 grams per square meter g/m 3 grams per cubic meter g/ml grams per milliliter gal gallons GIS Geographic Information Systems gpd gallons per day ha hectares i.e. (lat.) id est that is IFAS Institute of Food and Agricultural Sciences ILPM Internal Loading Phosphorus Model in. inches in toto (lat.) completely 4/10/2003 engineers & scientists TOC-6

9 k e light extinction coefficient kg kilograms km kilometers km 2 square kilometers L/kg liters per kilogram lbs pounds LEC Lower East Coast LOHTM Lake Okeechobee 3-D Hydrodynamic Transport Model LOOP Lake Okeechobee Operating Permit LORSS Lake Okeechobee Regulation Schedule Study LOWQM Lake Okeechobee Water Quality Model m meters m 2 square meters m 3 cubic meters m 3 /day cubic meters per day m 3 /hr cubic meters per hour m 3 /min cubic meters per minute mg milligrams mgd million gallons per day mg/g milligrams per gram mg/kg milligrams per kilograms mg/l milligrams per liter mg/m 2 - day milligrams per square meter per day mg/m 2 - year milligrams per square meter per day mg P/g milligrams of phosphorus per gram mg P/kg milligrams of phosphorus per kilogram mg P/L milligrams of phosphorus per liter mg P/m 2 milligrams of phosphorus per square meter mg P/yr milligrams of phosphorus per gram mi miles mi 2 square miles mm millimeters N/m 2 Newtons per square meter N 2 Nitrogen NH 3 Ammonia - NO 3 Nitrate NAIP non-apatite inorganic phosphorus NGVD National Geodetic Vertical Datum + NH 4 Ammonium NPV net present value NRPA Natural Resources Protective Association O&M Operations & Maintenance OM&M Operation, Maintenance, and Monitoring P phosphorus PM Performance Measure 4/10/2003 engineers & scientists TOC-7

10 PEC probable effects concentration ppm parts per million RI/FS Remedial Investigation/Feasibility Study SAV submerged aquatic vegetation SFWMD South Florida Water Management District Si silica SIC Standard Industrial Classification SPSS Statistical Package for the Social Sciences SRP soluble reactive phosphorus STA stormwater treatment areas SWAN Simulating WAves Near-shore SWIM Surface Water Improvement and Management TMDL Total Maximum Daily Load TN total nitrogen TP total phosphorus TN:TP ratio of total nitrogen to total phosphorus TR tax revenue TSS total suspended solids µg P/L micrograms of phosphorus per liter µg/l micrograms per liter USACE United States Army Corps of Engineers USEPA United States Environmental Protection Agency USFWS United States Fish and Wildlife Service viz. (lat.) videlicet namely w/w wet weight y 2 square yards 4/10/2003 engineers & scientists TOC-8

11 Executive Summary This Lake Okeechobee Sediment Management Feasibility Study, prepared by Blasland, Bouck & Lee, Inc. (BBL), Tetra-Tech, Inc., Environmental Quality Inc., and Haysmar, Inc., presents the results of a three-year scientific and engineering evaluation of management options designed to address elevated levels of phosphorus in the mud sediments of Lake Okeechobee. Public and interagency outreach efforts were successful in gathering critical input that shaped each phase of this study. Although it is recognized that excessive inputs of phosphorus from external sources are the primary driver of high concentrations of phosphorus in lakes, the occurrence of high concentrations of phosphorus in the water column of Lake Okeechobee is believed to be exacerbated by internal sources, namely high levels of phosphorus in the sediments. This is because Lake Okeechobee is quite broad and shallow, which creates an environment where bottom sediments enriched in phosphorus can be physically resuspended into the water column by wind-induced waves. Once introduced into the water column, phosphorus that is loosely bound to sediment particles or dissolved in the sediment porewater can become available to phytoplankton, stimulating their growth. Internal phosphorus loading also occurs as a result of natural chemical and biological processes. Together, these internal releases of phosphorus to the water column are hypothesized to contribute to increased frequency of blue-green algae blooms and decreased water quality in the lake. Moreover, some believe that if internal loading is not addressed, the lake may not respond to reductions in external phosphorus inputs (Steinman et al., 1999), or the response may be significantly delayed. This report addresses the following basic questions: What will happen to the lake if no active in-lake measures are taken to address phosphorus in the sediments? How long will it take the lake to recover if only reductions in external loads are addressed? Of the feasible alternatives, which is the most effective for addressing phosphorus loading in the lake? How long will the alternative take to implement? How much will the alternative cost? 4/10/2003 engineers & scientists ES-1

12 What are the potential impacts and benefits (environmental, economic, other) of the alternative? Thirty-six potential sediment management options with the potential to address internal loading were initially screened on the basis of effectiveness, implementability, risk, reliability, and applicability to Lake Okeechobee (BBL, 2001b). Following the screening process, the alternatives listed below were retained for full-scale evaluation: No In-Lake Action; Chemical Treatment Using Aluminum Sulfate (alum) and Sodium Aluminate; and Dredging. Each alternative listed above is evaluated in this Feasibility Study with respect to the five goals established for the project (BBL, 2001a): Maximize water quality improvements; Maximize engineering feasibility and implementability; Maximize cost effectiveness; Maximize environmental benefits; and Maximize socioeconomic benefits. Each alternative was evaluated against 26 clearly defined performance measures related to the five primary project goals (see Section 2). The evaluation incorporated water quality modeling results, along with engineering evaluations, detailed cost estimates, interviews, case study reviews, socioeconomic analyses, and public and interagency input. Uncertainties related to the findings presented in this Feasibility Study are associated with the expectation that the current Total Maximum Daily Load (TMDL) established for Lake Okeechobee by the Florida Department of Environmental Protection (FDEP, 2000) can be achieved by Per the direction of the South Florida Water Management District (District), all analyses are based on the assumption that external phosphorus loads will be reduced to the TMDL of 140 metric tons by If achievement of the TMDL goal is delayed, the results predicted in the modeling analyses presented 4/10/2003 engineers & scientists ES-2

13 in this FS would be pushed back by an equivalent time period (i.e., if the TMDL target is not achieved until 2025, all timeframes discussed in items 1 through 3 below would be delayed by 10 years). Additional alternative specific uncertainties are discussed in Sections 3, 4, and 5. The results of this Feasibility Study are briefly summarized as follows: 1) No In-Lake Action assumes that the external loading rate of phosphorus (P) will be reduced to a total load of 140 metric tons per year by 2015 in accordance with the TMDL established for the lake. No In-Lake Action is decidedly not a do nothing approach. While there are no active in-lake sediment management activities, this alternative incorporates extensive lake and watershed monitoring efforts and aggressive watershed management practices to achieve restoration goals for Lake Okeechobee. For the purpose of modeling, external loads were converted to concentrations. The phosphorus concentration and external loading reduction schedule assumed in the modeling analysis (described in Section 3) consists of three parts: Baseline conditions start in 2000 with an initial load that reflects the average load for the previous 10 years. The external total phosphorus (TP) load is assumed to decline linearly by 25% between 2000 and This reduction is attributed to the implementation of best management practices (BMPs) in the watershed. Between 2010 and 2015, the external load is assumed to decline further to the TMDL goal, also as a result of watershed management. Modeling results for the No In-Lake Action scenario indicate a 25% decrease in the annual frequency of algal blooms (from a current annual likelihood of approximately 20%), to below a 15% annual probability of a bloom occurrence by 2015 and a decrease to below 10% by Steady-state lake recovery conditions would be achieved around 2063, approximately 35 years from the point that external loads are reduced to the inflow load of 140 metric tons (see Section 3). 4/10/2003 engineers & scientists ES-3

14 2) Chemical Treatment, using alum and sodium aluminate, is estimated at a cost of approximately $493 million. Chemical treatment would start about year 2012 and would take 3 years to complete. Modeling results and technical evaluations indicate that chemical treatment would effectively inactivate the upper 10 centimeters of phosphorus in existing sediment and much of the new phosphorus introduced into the sediments for about 15 years. With chemical treatment, the target of an annual likelihood of algal bloom occurrence of 10% (or less) in the near-shore region is achieved approximately 15 years earlier than predicted for the No In-Lake Action alternative. Chemical treatment also reduces the time to reach the in-lake TP goal compared to the No In- Lake Action alternative. Under the No In-Lake Action scenario, the Internal Loading Phosphorus Model (ILPM) and Lake Okeechobee Water Quality Model (LOWQM) predict Lake Okeechobee will achieve 90% of the in-lake target concentration of 40 micrograms per liter (µg/l) by approximately years 2033 and 2042, respectively. If alum were applied to the lake according to the protocols of the chemical treatment alternative, both models predict that Lake Okeechobee would show improvements quite rapidly. Specifically, reductions in pelagic TP concentrations reach 90% of the predicted steady state recovery concentration by 2015, which is approximately 20 to 30 years earlier than the No In-Lake Action alternative. Beyond 15 years, the concurrent reductions in external loads are primarily responsible for improvements in water quality. If reductions in external loads are delayed or are not achieved, chemical treatments would have to be repeated about every 15 years to maintain the steady state recovery conditions (see Section 4). 3) Dredging, using hydraulic dredges, is estimated at a cost of approximately $3 billion. Dredging would start about 2015 and would take 15 years to complete. The technical evaluations and water quality modeling completed for this study indicate that dredging can never remove all the targeted sediment and the layer left behind regardless of its thickness would continue to release phosphorus into the water column. Hence, this alternative shows limited or no effectiveness (see Section 5). 4/10/2003 engineers & scientists ES-4

15 1. Introduction This Evaluation of Alternatives report represents the cornerstone of the three-year Lake Okeechobee Sediment Management Feasibility Study (FS). The study, commissioned by the South Florida Water Management District (the District) in 2000, was designed to analyze possible approaches to reduce internal phosphorus loading in Lake Okeechobee and included both a comprehensive technical assessment and an extensive public and interagency outreach effort. The primary component of the outreach effort was a series of four public meetings, but also included distribution of fact sheets to more than 800 interested individuals, development of a project website, establishment of a document repository, placement of meeting notices in local newspapers, and personal contact with key representatives of the public and government agencies. The public outreach effort was critical to the progress of the study, and yielded valuable input and insight that was considered and incorporated throughout the three-year process. This report is the culmination of the technical evaluation. It satisfies both the overall charge of the study and the regulatory requirements (described in Section 1.3), and provides the District with thorough, defensible quantitative and qualitative information that can be used to develop a plan for the future of Lake Okeechobee. 1.1 Background Lake Okeechobee, the second largest freshwater lake wholly within the continental United States, is the liquid heart of south Florida. Located at the center of the Kissimmee-Okeechobee-Everglades aquatic ecosystem, this expansive (nearly 730 square miles [mi 2 ]), relatively shallow (average current depth of just 9 feet [ft]) water body is fed primarily by the Kissimmee River and serves as the headwaters to the Caloosahatchee River, several canals, and the Everglades (Figures 1-1 and 1-2). The lake s shores touch five counties, and the drainage basin covers more than 4,600 mi 2. The lake typically contains more than 1 trillion gallons of water and plays a central role in regional water storage and supply for urban drinking water (Florida Administrative Code [FAC] Rule ), 4/10/2003 engineers & scientists 1-1

16 irrigation of agricultural lands, and flood control. Lake Okeechobee is also ecologically important to the region it is a major water source to the Everglades and provides critical habitat for fish, birds, and other wildlife, including the federally endangered Everglades snail kite (Aumen and Gray, 1995). Conditions in Lake Okeechobee have changed dramatically over the last century, largely as a result of external loading nutrient inputs, in particular phosphorus, to the ecosystem from agriculture and other human activities in the watershed (Havens et al., 1996). The legacy of decades of high external loads of phosphorus to the lake is sediment with elevated concentrations of phosphorus (Figure 1-3), primarily in the pelagic zone. The higher concentrations of phosphorus are primarily in the pelagic mud zone in the center of the lake. The deeper sediments in the pelagic zone contain an estimated 51,600 metric tons (~56,760 tons) of phosphorus (see Figure 1-4 for spatial distribution of sediment types and habitat regions of the lake). This phosphorus-laden sediment may be frequently resuspended in the water column by wind and waves (Maceina and Soballe, 1990), and this internal loading has been reported to contribute phosphorus to the lake s water as a rate approximately equal to the contribution from external loading (Moore et al., 1998). It has been theorized that, if this high rate of internal loading is not addressed, the lake may not respond to reductions in external phosphorus inputs (Steinman et al., 1999), or the response may be significantly delayed. Concerns have been raised that, unless addressed in some way, the relative contribution of this internal source may even increase as the external sources are mitigated (Moss et al., 1999). 1.2 Purpose of the Feasibility Study The purpose of the Lake Okeechobee Sediment Management Feasibility Study is to evaluate a base case of No In-Lake Action against a variety of active sediment management options to address the potential internal phosphorus loading issue, bearing in mind the overall objective of substantially reducing in-lake phosphorus concentrations, improving water quality and water clarity, and reducing blue-green algae blooms. 4/10/2003 engineers & scientists 1-2

17 The Lake Okeechobee FS, which evolved with public and private involvement over the last three years, was commissioned in September 2000 by the District and conducted by Blasland, Bouck & Lee, Inc. (BBL) and its partners, Tetra-Tech, Inc., Environmental Quality, Inc., and Haysmar, Inc. 1.3 Regulatory Drivers This FS was specifically required by the Lake Okeechobee Protection Act, House Bill 991 [now Florida Statute (3)(f)], under the Lake Okeechobee Internal Phosphorus Management Program, which states, By July 1, 2003 the District in cooperation with the other coordinated agencies and interested parties, shall complete a Lake Okeechobee internal phosphorus load removal Feasibility Study. The Feasibility Study shall be based on technical feasibility as well as economic considerations and address all reasonable methods of phosphorus removal. If methods are found to be feasible, the District shall immediately pursue the design, funding, and permitting for implementing such methods. In addition, this study was driven by the Lake Okeechobee Issue Team Action Plan (Harvey and Havens, 1999) and was designed to support management decisions by the District s Governing Board. Overall, the goals for this project must remain consistent and compatible with the goals that have been set forth in the following: The Central and South Florida Project Comprehensive Review Study (United States Army Corps of Engineers [USACE], 1999a), which has evolved into the Comprehensive Everglades Restoration Program (CERP), led by the USACE and the District; The Surface Water Improvement and Management (SWIM) Plan (SFWMD, 1997); The Lower West Coast Water Supply Plan (SFWMD, 2000a); The Lower East Coast Water Supply Plan (LEC Plan; SFWMD, 2000b); and The Lake Okeechobee Regulation Schedule Study (LORSS) conducted by the USACE (1999b). 4/10/2003 engineers & scientists 1-3

18 1.4 Feasibility Study Process The three-year FS was designed to progress in five major stages or tasks: Task 1 Establishment of goals and performance measures (BBL, 2001a) and preparation of a public outreach plan (BBL, 2000); Task 2 Development of a specific array of alternatives to be evaluated in detail in the Feasibility Study (BBL, 2001b); Task 3 Preparation of a work plan for conducting the detailed evaluation of alternatives (BBL 2002); Task 4 Detailed evaluation of the alternatives (the focus of this document); and Task 5 Prioritization of alternatives, weighting of performance measures, and selection of an appropriate course of action. Tasks 1 through 3 were finalized in 2001 and 2002 and were developed in cooperation with the public, the regulatory community, and private entities. This document presents Task 4 the detailed evaluation of the alternatives, which is the culmination of the technical portion of the FS process. As mentioned above, the purpose of the FS is to evaluate sediment management options and to compare these to a No In-Lake Action baseline scenario to evaluate the resulting impact on internal phosphorus loading. The overall goal for lake-wide average phosphorus concentrations is tied to the Total Maximum Daily Load (TMDL) goal of 140 metric tons, set in both the Lake Okeechobee Action Plan (Harvey and Havens, 1999) and the District s SWIM Plan (SFWMD, 1997). The five main goals of the project, were developed during Task 1 with input from interested parties and the public and presented in the Goals and Performance Measures report (BBL, 2001a). The goals are as follows: Goal 1 Maximize water quality improvements; Goal 2 Maximize engineering feasibility and implementability; Goal 3 Maximize cost effectiveness; Goal 4 Maximize environmental benefits; and Goal 5 Maximize socioeconomic benefits. 4/10/2003 engineers & scientists 1-4

19 Twenty six performance measures associated with the above-referenced goals, which were also developed collaboratively with the public and regulatory communities, are summarized in Section 2 and described in more detail in Appendix F. Following an initial screening of a wide range of available sediment management technologies and process options, 36 were deemed potentially applicable for managing internal phosphorus loading in Lake Okeechobee. These 36 options were evaluated in detail in the Development of Alternatives report (BBL, 2001b) with respect to potential feasibility for use in the lake. The four screening criteria initially applied were: effectiveness, implementability, applicability to Lake Okeechobee, and risk and reliability. As a result of the assessment process, the project team screened out the technologies and specific process options that were not feasible for use in Lake Okeechobee. This evaluation was based on the four screening criteria listed above, numerous case studies, findings and information presented in current research, vendor information, and considerations unique to Lake Okeechobee. The 14 technologies and process options retained were used as building blocks to create a set of sediment management alternatives, that if implemented, could potentially meet the objective of reducing internal phosphorus loading. A complete list of the initial sediment management options, the detailed evaluations of each technology and process option, and a summary of those technologies retained for further consideration, is provided in the Development of Alternatives report (BBL, 2001b). In Task 3, the team developed the Work Plan for the Evaluation of Alternatives, a work breakdown structure in essence a detailed road map for coordinating and completing the evaluation of alternatives (BBL, 2002). The processes identified in Task 3 are applied here in the formal evaluation stage (Task 4). The primary objectives of the analyses presented in this report are to determine the feasibility and potential overall effectiveness of each alternative, and provide the District with 4/10/2003 engineers & scientists 1-5

20 defensible quantitative and qualitative data that can be readily used in Task 5 to prioritize the alternatives and select an appropriate future course of action for Lake Okeechobee. As part of the alternative evaluation process, the initial list of alternatives was refined to the following No In-Lake Action with monitoring of external loads (see Section 3), Chemical Treatment with aluminum compounds (see Section 4), and Hydraulic Dredging with various post-dredge sediment management scenarios (see Section 5). These alternatives represent the possible range of options that could be implemented in the lake. The remainder of this Evaluation of Alternatives report addresses the following basic questions: What will happen to the lake if we do nothing active to address phosphorus in the sediments? How long will it take the lake to recover if we address reductions in external loads only? Of the feasible alternatives, which is the most effective for addressing phosphorus in the lake? How long will the alternative take to implement? How much will the alternative cost? What are the potential impacts and benefits (environmental, economic, other) of the alternative? 1.5 For More Information This Feasibility Study is an ongoing process that is an important part of charting a future course for Lake Okeechobee. With the review of the alternatives and the weighting of the performance measures still ahead (Task 5), the District welcomes public and interagency involvement in the process. For more information, access to other reports, and news regarding this Feasibility Study, please visit the project website at or contact the District Project Manager, as follows: Jorge Patino, P.E. South Florida Water Management District Phone: (561) Fax: (561) [email protected] 4/10/2003 engineers & scientists 1-6

21 2. Approach to Evaluation of Alternatives 2.1 Overall Approach The overall goal of the FS evaluation was to perform an objective science- and engineering-based analysis of the feasibility of each alternative and, to the extent possible, to evaluate the expected performance of each alternative within Lake Okeechobee. To meet this goal, a consistent approach was required to minimize bias or error in the method, results, or reporting. The same methods, tools, and data prescribed under each performance measure were used to evaluate the merits of each alternative. In this way, the relative feasibility and performance of each alternative is estimated and compared against that performance measure s target value or condition. This report incorporates, to the extent possible, the information generated during Environmental Associates (EA s) pilot dredging project (EA, 2002a and 2002b), the findings of the lake sediment phosphorus dynamics study as reported by the team from the University of Florida under the direction of Dr. Ramesh Reddy (Reddy et al., 2002), and the findings of the beneficial reuse study prepared by OA Systems (OA, 2002). In addition to the most current data and technical knowledge, BBL gathered input from appropriate local, state, and federal agencies and considered feedback received during all four public/interagency meetings. Several methods were used to evaluate the sediment management alternatives. Computer modeling was performed to quantitatively assess the water quality impacts of each alternative in the near and long term. A public and interagency outreach process was developed and implemented to identify concerns and issues in the local and regional communities. Data relating to sediment quality, water quality, socioeconomic conditions, submerged aquatic vegetation, wildlife, and existing and future land use were reviewed to develop an understanding of where the potential impacts and/or benefits would occur with any given sediment management alternative. A brief discussion of activities performed to assess the alternatives is provided below. 4/10/2003 engineers & scientists 2-1

22 2.1.1 Modeling The two primary models used to simulate the no action, chemical treatment, and dredging scenarios are as follows: 1) Lake Okeechobee Water Quality Model (LOWQM; James and Bierman, 1995; Bierman and James, 1995; James et al., 1997; Jin et al., 1998); and 2) Internal Loading Phosphorus Model (ILPM; Pollman, 2000). The LOWQM and ILPM models have both been calibrated to Lake Okeechobee and are used to simulate the long-term effects of external nutrient reduction scenarios on total phosphorus dynamics in the pelagic zone of the lake. The LOWQM also is used to simulate changes in nitrogen dynamics, total nitrogen to total phosphorus (TN:TP) ratio, and chlorophyll a. The LOWQM also has recently been revised to improve how diagenesis of phosphorus in the surficial sediments is represented (James et al., in preparation). Short-term effects were predicted using the Lake Okeechobee 3-D Hydrodynamic Transport Model (LOHTM), which was developed explicitly for Lake Okeechobee by Jin and Hamrick (2000) from Hamrick and Wu s (1997) Environmental Fluid Dynamics Code (EFDC). LOHTM is a threedimensional, dynamic model that was designed to examine circulation patterns and vertical mixing lakewide. The model has a grid structure of 58 x 66 horizontal cells, each cell being 925 meters (m) to a side, with six vertically stretched cells (i.e., each cell is 1/6 of the water depth), yielding a total number of 2,216 active water cells (Jin and Hamrick, 2000). When linked with Delft University s Simulating WAves Near-shore (SWAN) model, which predicts wind-wave parameters, LOHTM can be used to predict the varying concentrations of total suspended solids (TSS) across the lake (spatial) and over time in response to changing meteorological and physical conditions. The modeling results, as they relate to each alternative, are described in detail in Sections 3, 4, and 5. 4/10/2003 engineers & scientists 2-2

23 2.1.2 Public and Interagency Outreach A series of four public and interagency meetings were held at key junctures throughout the Feasibility Study process as described in the Public Outreach Plan (BBL, 2000). These meetings were held in Belle Glade, Moore Haven, Okeechobee, and West Palm Beach. The goal of the outreach process was to inform the community at large about the issues associated with the internal loading of phosphorus and to gather input regarding the information generated throughout the study. Preparation of reports (i.e., Goals and Performance Measures, Development of the Alternatives, Work Plan, and this Evaluation of Alternatives) for this project was performed in a collaborative and interactive manner with assistance from Florida Fish and Freshwater Conservation Commission (FWC), USACE, the District, and other interested parties. Once finalized, documents were posted on the web and mailed to any individual or organization requesting hard copies. Public notices, fact sheets, letters, and invitation cards were mailed to more than 700 people prior to each of the public meetings. Follow-up calls were made to about 30% of the individuals and groups on the mailing list to ascertain that everyone had the information needed. A stakeholder database, as well as the materials and minutes generated for each of the outreach meetings, is provided in Appendix C. The alternative-specific feedback provided as part of the outreach process is presented in Sections 3, 4, and 5, as applicable Data Collection and Review Lake Okeechobee-specific literature searches were performed for relevant information related to sediment treatment for phosphorus loading, water quality, limnology, sediment quality, sediment biogeochemistry, land acquisition, permitting, and wildlife. A number of interviews were also conducted with FWC staff members to develop an understanding of current habitat and wildlife conditions on the lake. A list of sources and resources is provided at the end of the reference section of this document (Section 7). The applicable information gathered during these searches is provided in the alternative-specific evaluations in Sections 3, 4, and 5. 4/10/2003 engineers & scientists 2-3

24 Sediment Characterization Recognizing the fundamental importance of understanding the lake s sediment characteristics, published data related to sediment quality in the lake were reviewed and additional samples were collected and analyzed to fill certain data gaps. A brief summary of the sediment characteristics is provided below. For the purposes of this Feasibility Study, the sediments targeted for management actions are those located in the central pelagic mud zone of Lake Okeechobee (Figure 1-4). Covering approximately 83,000 hectares (ha), or about 44% of the lake s total surface area (Reddy, 1991a), the mud zone is estimated to contain approximately 193 million cubic meters (m 3 ) of phosphorus-rich sediments (Kirby et al., 1989). 1 The sediments in the mud zone range from a few centimeters (cm) in depth at the periphery to over 75 cm in depth at the central, deepest section of the lake (Kirby et al., 1989) and are composed of 25% organic matter, 25% carbonate matter, and 50% inorganic residue (Reddy, 1991a; Brezonik and Engstrom, 1998). The mud sediments are characterized as black organic-rich muds (Kirby et al., 1989) and are estimated to contain 84.2% water by weight (Reddy, 1991a). Analytical testing of sediment cores obtained from the mud zone indicate that total phosphorus (TP) in the mud sediments ranges from approximately 200 to 2,000 milligrams per kilogram (mg/kg), with the highest concentrations in the upper mud layers (Fisher et al., 2001; Engstrom and Brezonik, 1991). Further evaluation of the data from Engstrom and Brezonik (1997; peer-reviewed/open literature publication of 1991 results) suggests that TP concentrations in the upper 10 cm and upper 30 cm average approximately 1,200 mg/kg and 990 mg/kg, respectively (Figure 2-1). 1 It is interesting to note that concentrations of total phosphorus in Lake Okeechobee are not unusually high for Florida lakes. In a study of 97 Florida lakes spanning a broad range of trophic states, the concentrations of TP in surficial (top 2 cm) sediments averaged 1,600 mg/kg (Brenner and Binford, 1988) and ranged as high as 8,090 mg/kg. In Lake Okeechobee, the average concentration of TP in the top 1 cm of mud zone sediments is 1,310 mg/kg (data from Engstrom, personal communication), nearly 20% lower than the average reported by Brenner and Binford. 4/10/2003 engineers & scientists 2-4

25 Kirby et al. (1989) found that the sediments in the mud zone were overlain by a fluid mud veneer up to 8 cm thick. This overlying fluid mud layer was found to have no measurable shear strength and a density of 1.01 to 1.03 grams per cubic centimeter (g/cm 3 ). Density of the underlying, more consolidated mud layer was found by Kirby et al. (1989) to range upwards to 1.2 g/cm 3, with a maximum density of 1.3 g/cm 3. The median density of the surficial 10 cm of the sediment is g/cm 3 (data from Reddy et al., 2002). Additional chemical, geotechnical, and elutriation tests were performed for sediment core samples acquired by BBL during September and October These data, as presented in Appendix B and discussed in Section 5, have been used to conduct portions of the engineering evaluations in this FS. Dry bulk density results are presented for sectioned sediment cores from 26 stations. The average of the 26 core intervals taken from 0-15 cm was 0.14 grams per milliliter (g/ml) 2, while the average of the 26 core intervals from 15 cm deep to base material was 0.23 g/ml. Eleven sediment samples had the following average geotechnical properties: 33.9% organics; 35.2% moisture content; 23.2% solids (wet weight [w/w]); 2.17 g/ml solids specific gravity; and 0.27 g/ml dry density. Sieve analyses averaged 69.7% passing #200 sieve, with average sand content of 30.3%. Evaluations of sediment heavy metal analyses are presented in Appendix B. The sediment data for 13 metals were compared to Florida Department of Environmental Protection (FDEP) Cleanup Target Levels (CTLs) for Soil and to the United States Environmental Protection Agency s (USEPA's) June 2000 probable effects concentration (PEC) levels for fresh water sediments. None of the sediment samples exceeded PECs for fresh water; however, many of the samples exceeded FDEP cleanup target levels for arsenic in soil. Because of these exceedances for arsenic, reuse of sediments applied in the region as soil blended material would likely require additional management such as institutional controls. Elutriation tests for three samples showed, after resuspension and settling, that supernatant phosphorus concentrations were not elevated (and were actually reduced slightly), while the 24-hour elutriate showed elevated turbidity, suspended solids, aluminum, and iron concentrations. 2 Note that for density measurements, results reported as either g/ml or g/cm 3 are equivalent. Units are presented as in published reports. 4/10/2003 engineers & scientists 2-5

26 Internal Loading Evaluation As evident from the literature, internal loading results from the complex interplay of dynamic physical, chemical, and biological processes in the lake. Appendix A provides a summary of the literature available regarding internal loading and a theoretical framework of the conceptual model. Many aspects of this conceptual model have been developed extensively by Havens et al. (2000) and Havens and Schelske (2000). Rather than reproduce that work here, we have included both papers in Appendix A. In general, internal loading refers to the resupply or recycling of phosphorus within the lake, principally from the sediments. Virtually all lakes function over long time scales as net sinks for phosphorus (i.e., lakes receive more phosphorus from external sources than they export). Depending on the form as it enters the lake, phosphorus can initially be (1) taken up directly by primary producers (soluble inorganic phosphorus); (2) metabolized in the water column by bacteria (labile organic phosphorus), and then taken up by primary producers; or (3) deposited in the sediments as organic and inorganic particulate phosphorus (see, for example, Rigler, 1975; Wetzel, 1975; Lampert and Sommer, 1997). Regardless of its initial fate, a significant fraction of the phosphorus entering the lake eventually is deposited in the sediments. This is because decomposition of organic matter is rarely wholly efficient or complete in mineralizing and releasing phosphorus. This deposited phosphorus continues to mineralize, and as a result, concentrations of dissolved inorganic phosphorus in the sediment porewaters can build up to concentrations several orders of magnitude in excess of dissolved inorganic phosphorus concentrations in the overlying water column. Internal loading results when phosphorus from this enriched pool is introduced into the water column, either through wind-wave induced resuspension of sediment particles containing comparatively high concentrations of exchangeable phosphorus, or through more passive exchange processes, such as bioturbation (Figure 2-2) Socioeconomic Evaluation In order to evaluate the impacts or benefits associated with various alternatives that might be implemented in Lake Okeechobee, it was necessary to benchmark baseline economic conditions in the region of the Lake Rim. As described in the Work Plan, two data matrices were constructed to support 4/10/2003 engineers & scientists 2-6

27 an economic description, and a third data set was compiled to specify the demographic characteristics of the region. The description of the socioeconomic make-up of the Lake Okeechobee Rim and the resulting evaluations of alternatives rests on three databases. Two economic data sets were used to complement each other in constructing a description of the nature and primary activities of the region s economy. One database contained U.S. Department of Commerce 2-digit Standard Industrial Classification (SIC) data for 2000 and This database contained information on total revenues, number of establishments, total employment, and number of establishments with annual revenues of $1 million or more. The other economic database contained data on gross revenues reported to the Florida Department of Revenue (DOR) for 1997 through This database contained information on the number of establishments, total revenues, taxable revenues, and total taxes paid. The demographic database contained information on population, income, and ethnic and cultural subpopulations from the 1990 census, the 2000 census, and an estimate for the year The SIC database and the demographic database were specified by zip code boundaries. The DOR database was specified by mailing address. The zip code areas were matched to the addresses, or, where necessary, combined to achieve congruence. Six geographic sub-areas encompassing the entire lake rim were defined for the study. The data was manipulated using the Statistical Package for the Social Sciences (SPSS) and Excel spreadsheet functions. The demographic census and SIC data were obtained from Claritas, Inc., a commercial data firm. The DOR data was obtained from the University of Florida s Bureau of Economic and Business Research and from the DOR. A summary of the baseline economic evaluation of the lake and vicinity is provided in Appendix D. Alternative-specific socioeconomic evaluations are provided in Sections 3, 4, and 5. 4/10/2003 engineers & scientists 2-7

28 2.1.5 Case Study Reviews Case studies for a wide variety of sediment management options were evaluated in detail at the screening level and presented in BBL s Development of Alternatives document (BBL, 2001b). Case studies related to no in-lake action, chemical treatment, and dredging are discussed, where appropriate, throughout Sections 3, 4, and 5 of this document Cost Estimating Estimated costs were developed for each of the alternatives, based on a review of chemical and geophysical characterization data and the results of bench- and pilot-scale studies. The estimates further rely on realistic assumptions of the areal extent and depths of response actions and the capabilities of available equipment. These assumptions were then used to develop material balances for the estimation of sizing, labor, and operating expenses and construction sequencing and durations. Cost estimates were developed using guidance from the USEPA (2000). Unit costs are in 2002 dollars and are estimated from published guides (e.g., Means Site Work and Landscape Cost Data), vendor quotations, professional judgment, and experience gained during other sediment projects. Present worth was estimated using a 5.8% beginning-of-year discount rate (adjusted for inflation) considering policy directive from the USEPA (1993). These estimates are consistent with the accuracy of FS-level costs (+50/-30 %) using remedial investigation/feasibility study (RI/FS) guidance (USEPA, 1988). 2.2 Evaluation Process Each alternative or potential course of action has been evaluated based on its ability to achieve the stated goals and performance measures and to ultimately contribute in a meaningful way to the restoration of Lake Okeechobee. The overall goals are broken down into several specific measurable objectives (i.e., performance measures). The associated target, tools, critical data, method, and score for evaluation of each performance measure are presented based upon the following definitions/approach: 4/10/2003 engineers & scientists 2-8

29 Performance Measure Each performance measure represents a particular aspect of the project s five overall goals. When assessment of each performance measure was carried out, enough specific and relevant information was generated to develop a clear picture of not only whether an alternative could be expected to achieve the stated goals, but also to what extent and under which conditions, assumptions, and timeframes. Target Each performance measure has a target, which is the specific level, quantity, or condition desired or deemed necessary to assume achievement of a goal or significant progress toward achieving a goal. For example, the target water column concentration of TP to be achieved by an alternative is 40 micrograms per liter (µg/l). Performance measure targets are mandated by state or other laws or regulations, or are based on site-specific testing, experience, or other sound scientific or engineering judgment. Tool(s) In order to carry out the evaluations, a number of different tools, both quantitative and qualitative, were used to estimate each alternative s feasibility and performance. Tools applied ranged from mathematical models to literature surveys and correlation matrices. Critical Data/Input Evaluation of alternatives against each performance measure required certain data or input; therefore, each performance measure discussion includes a brief description of data and data sources that were critical to performing the evaluations. In many cases, output data generated during the evaluation of one performance measure (e.g., water quality) were used as critical input during the evaluation of another measure (e.g., habitat quality, downstream impacts). Method The method discussion provides important details as to how the performance measure and tools were used to evaluate each alternative. For example, computer-based modeling was performed or appropriate assessment criteria (e.g., site-specific or case-study data and experience, data collected during pilot-scale test projects) were applied to determine the expected outcome of an alternative relative to a particular goal. For cost-estimating activities, the method description includes information on how the estimates were developed and reported. 4/10/2003 engineers & scientists 2-9

30 Scoring The outcome of the evaluation of alternatives relative to performance measures was reported either quantitatively or qualitatively, depending on specific target parameters and the availability of hard data. In some cases, quantitative metrics produced raw results in units (metrics) appropriate to each performance measure (e.g., dollars, µg/l). Other performance measures have metrics that are qualitative. Scoring for performance measures are reported on a simple scale ranging from 1 to 5. For example, a relative value of 1 was assigned for the lowest or least favorable performance, and 5 was assigned for the highest or most favorable performance of an alternative. Where appropriate, the evaluation of some performance measures may generate two scores one related to short-term impacts or benefits, and the second to the long-term impacts or benefits. Scores (i.e., outcomes) of the evaluations are reported in two ways in this document. First, the scores for all alternatives are presented at the end of each performance measure discussion in the text of this FS. Secondly, at the end of the evaluation process (Summary and Recommendations, Section 6 of this FS), all scores have been compiled into a single table to allow for a convenient comparison of how each alternative performs relative to all performance measures. A summary of the specific targets, tools used, data reviewed, method of analysis, scoring interrelationships with other goals, and uncertainties associated with each goal and performance measure is provided below. GOAL 1: Maximize Water Quality Improvements Performance Measure 1A Minimize Time to Achieve Phosphorus Target Target: The time for lake water total phosphorus concentrations to reach 40 µg/l, or a fraction of this goal. Metric: Predicted phosphorous concentration as a function of time for a given external load and internal load reduction scenario. 4/10/2003 engineers & scientists 2-10

31 Tool(s): LOWQM is the primary tool. Supplemental modeling with Lake Okeechobee ILPM (Pollman, 2000), Walker (2000) Lake Okeechobee Model, Lake Okeechobee Phosphorus Diagenetic Model. Critical Data/Input: Current sediment chemistry, vertical fine structure data on sediment chemistry and physical properties, including critical shear stress, and water column major ion chemistry. Assumed external loading schedule was carefully articulated by the District, and resulted in a concentration target of 40 µg/l achieved by Method: Modeling using principally LOWQM to simulate dynamic response of lake to alternatives; supplemental modeling to predict porewater chemistry changes using thermodynamic models. Supplemental dynamic modeling using Lake Okeechobee ILPM (Pollman, 2000), and Walker (2000) Lake Okeechobee Model, as appropriate. Analyses of different alternatives, including the No In-Lake Action alternative, based on external loading scenario sufficient to produce a predicted long-term (steady state) in-lake total phosphorus concentration of 40 µg/l (the restoration target for this study). Scoring: Higher score means a more rapid rate of recovery. Interrelationships with Other Performance Measures/Timing: This evaluation comprises the fundamental framework for the evaluations for Performance Measures 1A, 1B, 1C, and 1D. Nitrogen loads defined as critical for 1D also were used in this analysis. Performance Measure 1B Maximize Reductions in Water Column Phosphorus Concentrations Target: Average total phosphorus concentration of 40 µg/l in the pelagic zone. Metric: Predicted pelagic lakewater TP concentrations and predicted load reductions required to achieve target concentration goal of 40 µg/l. 4/10/2003 engineers & scientists 2-11

32 Tool(s): LOWQM is the primary tool. Supplemental modeling with Lake Okeechobee ILPM (Pollman, 2000), Walker (2000) Lake Okeechobee Model, and Lake Okeechobee Phosphorus Diagenetic Model. Critical Data/Input: Current sediment chemistry, vertical fine structure data on sediment chemistry and physical properties, including critical shear stress, and water column major ion chemistry. Assumed external loading schedule was carefully articulated by the District, resulting in a target concentration of 40 µg/l achieved by Method: Modeling using principally LOWQM to simulate dynamic response of lake to alternatives; supplemental modeling to predict porewater chemistry changes using thermodynamic models. Supplemental dynamic modeling using Lake Okeechobee ILPM (Pollman, 2000), and Walker (2000) Lake Okeechobee Model, as appropriate. Analyses of different alternatives, including the No Action alternative, based on external loading scenario sufficient to produce a predicted long-term (steady state) in-lake total phosphorus concentration of 40 µg/l. Scoring: Higher score means average total phosphorus concentration at or near 40 µg/l. Interrelationships with Other Performance Measures/Timing: This evaluation comprises the fundamental framework for the evaluations for Performance Measures 1A, 1B, 1C, and 1D. Nitrogen loads defined as critical for 1D also were used in this analysis. Performance Measure 1C Maximize TSS Reductions in the Short Term and Long Term Target: The critical light extinction coefficient required to support the submerged aquatic vegetation community. Metric: Predicted TSS concentrations (milligrams per liter [mg/l]) in lakewater. TSS will then be used to compute the light extinction coefficient, k e. Compliance with FAC /10/2003 engineers & scientists 2-12

33 Tool(s): SWAN-LOHTM, LOWQM; supplemental modeling using thermodynamic models (see Performance Measures 1A/1B). Critical Data/Input: Relationship between the light extinction coefficient and TSS. Definition of k e,critical for submerged aquatic vegetation in Lake Okeechobee. Method: Simulate changes in TSS and light extinction coefficient, k e. Scoring: Higher scores mean greater TSS reductions and an increase in the maximum water depth able to support submerged aquatic vegetation in the near-shore zone (i.e., improved light transparency). Interrelationships with Other Performance Measures/Timing: Performance Measure 1A analysis (long-term) precedes this Performance Measure; results from this analysis support evaluation of Performance Measures 4A, 4B, and 4D. Uncertainty Conditions: Defining a quantitative relationship between light transparency and macrophyte community structure and standing crop is not very good; more qualitative ranking schemes were developed. Performance Measure 1D Minimize Algal Blooms Target: TP concentration < 40 µg/l; total nitrogen to total phosphorus ratio (TN:TP) > 30. Metric: TP concentrations; TN:TP. Tool(s): SWAN-LOHTM, LOWQM; supplemental modeling using thermodynamic models (see Performance Measure 1A). Critical Data/Input: Nitrogen loading scenarios must be defined. 4/10/2003 engineers & scientists 2-13

34 Method: Methods similar to those described for Performance Measures 1A/1B. LOWQM used to simulate TP and TN and the dynamics of three algal groups. Impact to near-shore region evaluated using regression relationship. Scoring: Higher score means lower incidence of blooms and reduced likelihood of cyanobacterial dominance of phytoplankton community. Interrelationships with Other Performance Measures/Timing: Analyses conducted for Performance Measures 1A/1B form the basis for this analysis. Nitrogen loadings developed for this analysis also must be incorporated into analyses of Performance Measures 1A/1B. Uncertainty Conditions: Magnitude of changes in nitrogen budgets that would occur concomitantly with reductions in phosphorus external loading rates. Change in internal recycling rates and NH + 4 release with sediment management, particularly sediment removal. Performance Measure 1E Minimize Exceedances of Water Quality Standards in the Short Term and Long Term Target: No exceedances of FAC or the Lake Okeechobee Operating Permit (LOOP) in the short or long term. Metric: Estimated chemical concentrations of constituents of concern in the water column based on available bulk sediment chemistry data and relevant case studies. Actual concentrations (in either mg/l or µg/l) of chemicals in surface water and sediment will be assessed in samples gathered during the Lake Okeechobee sediment dredging pilot study. Additional data could be gathered from samples collected elsewhere throughout the lake, as appropriate. Tool(s): SWAN-LOHTM; and information from case studies, vendors, and existing databases. 4/10/2003 engineers & scientists 2-14

35 Critical Data/Input: Concentrations of relevant constituents in Lake Okeechobee sediments and surface water; results of pilot dredging and University of Florida studies; and FAC and LOOP. Method: Short-term release rates estimated using relevant case study data and vendor information. Suspended sediment transport in lake (and associated contaminant concentrations) predicted by LOHTM. Scoring: Two scores were given one each for short- and long-term effects; higher scores mean fewer predicted exceedances. Interrelationships with Other Performance Measures/Timing: Performance Measures 1A, 1B, 1C, and 1D will precede this evaluation. Results were used in 1F, 2F, 5C, and 5D assessments. Uncertainty Conditions: Considerations discussed in the modeling write-ups apply here as well. Scaleability and applicability of case study information. Performance Measure 1F Minimize Downstream Impacts Target: Targets for other Performance Measures 1A through 1E. Metric: The water quality parameters listed in Goal 1 (phosphorus, TSS, algal bloom incidence, and short- and long-term water quality standards) will be estimated for water leaving the lake. Tool(s): Models and information as described in Performance Measures 1A through 1E. Critical Data/Input: Current water quality measurements at outlet points; descriptions and requirements of relevant activities. Method: Water quality modeling; results were compared to ultimate goal of 40 µg/l TP. 4/10/2003 engineers & scientists 2-15

36 Scoring: Higher score means net positive impacts. Interrelationships with Other Performance Measures/Timing: This evaluation was performed after assessments of Performance Measures 1A through 1E were complete. Results were considered in Performance Measures 5C, 5D, and perhaps 2F. Uncertainty Conditions: Current conditions are not adequately documented at outlet points, and ability to predict postremedial conditions at specific outlet points were limited. GOAL 2: Maximize Engineering Feasibility and Implementability Performance Measure 2A Maximize Technical Reliability Target: Sediment management alternatives that are considered highly reliable. Metric: The degree to which a technology has been demonstrated as reliable and effective over the long term at other sediment management sites will be qualitatively evaluated. The evaluation will also quantitatively consider the operation and maintenance (O&M) costs developed within Performance Measure 3B. Tool(s): Qualitative engineering judgment using information developed for the specific sediment management alternatives and case study/literature data. Critical Data/Input: A detailed description of the sediment management alternatives, data for other in-lake sediment-phosphorus management projects, and estimated O&M scope and costs for the sediment management alternatives. Method: Estimates of technical reliability were qualitatively developed using a combination of longterm performance data gathered from similar sites and a relative comparison of O&M scope and costs among alternatives. 4/10/2003 engineers & scientists 2-16

37 Scoring: Technologies with higher scores are indicative of greater reliability. Interrelationships with Other Performance Measures/Timing: This evaluation was completed once the detailed descriptions of the sediment management alternatives were developed, the literature review and case study data were compiled, and the O&M scope and cost estimates were prepared. Uncertainty Conditions: Inability to find data for projects that are similar in scope and size to Lake Okeechobee, the transferability of results from other projects, and the predictive limitations of long-term O&M cost estimates. Performance Measure 2B Maximize Technical Scalability Target: Technologies that have either been proven at a scale similar to Lake Okeechobee or are readily scaleable are preferable. Metric: The degree to which a technology within a given alternative has been used at a similar scale and/or the relative ease with which the technology implemented at a smaller scale can be scaled-up to meet the requirements of the Lake Okeechobee project. Tool(s): Qualitative evaluation using available case study and literature data, product literature, professional experience, and the results of available and applicable site-specific studies. Critical Data/Input: Detailed descriptions of the Lake Okeechobee sediment management alternatives, literature case study information for similar projects, and data for other Lake Okeechobee studies, as available. Method: Qualitative evaluation using the individual components of the sediment management alternatives. Case studies were reviewed along with Lake Okeechobee-specific study results. 4/10/2003 engineers & scientists 2-17

38 Scoring: Higher scores indicate that the approach is more likely to be scalable to meet the needs of this project. Interrelationships with Other Performance Measures/Timing: This evaluation was completed once the detailed descriptions of the sediment management alternatives were developed and the available and applicable literature case study data were compiled and reviewed. Uncertainty Conditions: The ability to find data for similar projects in the literature, the transferability of information from these other projects or vendor information to Lake Okeechobee, and the ability to estimate the ease of scaling up a specific technology. Performance Measure 2C Maximize Equipment and Material Availability Target: Maximize equipment and material availability. Metric: The availability of materials, equipment, and skilled workers will be assessed on a regional, national, and international basis. Length of lead times to obtain critical materials and equipment will also be evaluated. Tool(s): Quantitative and qualitative tools were used including information from suppliers, contractors, vendors, previous engineering experience, and information available from the literature. Critical Data/Input: Alternatives defined in terms of remedial objective, scope (remedial volume and extent), and schedule (production rates and construction management). Method: Equipment and material availability were qualitatively assessed using the tools indicated above. 4/10/2003 engineers & scientists 2-18

39 Scoring: Scores were assigned from 1 to 5, based on relative and predicted ability to implement (i.e., supply) construction of an alternative. A higher score (i.e., 5) would imply that sufficient equipment and materials are locally and readily available. Interrelationships with Other Performance Measures/Timing: Scope of alternatives must be as narrowly defined as possible prior to starting this evaluation, which was performed in conjunction with Performance Measures 3A and 3B. Uncertainty Conditions: Uncertainty in market forces is the primary concern (i.e., the demand for similar equipment and materials during the assumed construction time at this site). Equipment/method production rates and number of construction units in concurrent operation were assumed for alternatives, which may not accurately reflect how the alternative would ultimately be implemented by a construction contractor. Performance Measure 2D Maximize Permanence Target: An alternative that can provide optimal effectiveness over time and withstand normal windwave activity and infrequent events, such as hurricanes, is preferred. Metric: The degree to which the alternative uses technologies or approaches with a successful history of long-term performance and the degree to which the effectiveness of the technologies or approaches used within a given alternative is susceptible to the effects of normal wind/wave action or rare events, such as hurricanes. Tool(s): Quantitative and qualitative tools were used, including numerical models, case studies, and related literature. Results from the pilot dredging project will also be used to the extent available and applicable. 4/10/2003 engineers & scientists 2-19

40 Critical Data/Input: Data of specific interest include wave and storm data for Lake Okeechobee and results of computer modeling of related hydrodynamic and erosive forces. Predicted (modeled) postremedial phosphorus flux rates and assumed O&M requirement will also be considered. Method: A qualitative evaluation of the effectiveness of the processes and technologies were initially conducted using case study data from similar projects and related sources. Recovery projections generated using numerical models described in Performance Measures 1A though 1D will also be considered. Scoring: Permanence was rated using a relative scale of 1 to 5 (i.e., 5 for highest degree of permanence) based on qualitative and quantitative estimates of performance. Interrelationships with Other Performance Measures/Timing: Alternatives were defined prior to starting this evaluation. This evaluation was performed in conjunction with Performance Measures 1A, 1B, and 2A. Uncertainty Conditions: Uncertainty in the effectiveness of the technology and the projected duration of the remedy affect these evaluations. Performance Measure 2E Minimize On-Shore Land Use Needs and Conflicts Target: Minimize short- and long-term use of on-shore acreage and conflicts with public land uses in the vicinity of Lake Okeechobee. Metric: Acreage of on-shore property required by a given alternative. This includes long-term and short-term losses. The short-term losses include the time that construction support areas would be required in terms of years. 4/10/2003 engineers & scientists 2-20

41 Tool(s): Quantitative and qualitative tools were used in this evaluation, including estimating the acreage of on-shore land required by a given alternative, duration of long-term and short-term uses, and information pertaining to ongoing or planned public projects in the region. Critical Data/Input: Alternatives were defined in scope, duration, and timing to assess the on-shore land use requirements and the duration of such land uses. Method: A quantitative engineering estimate of the acreage of on-shore land required to support the implementation of the alternative and the duration of land use was made. The evaluation qualitatively assessed the potential conflict that a sediment management alternative might have with local or regional public projects. Scoring: Relative scores were assigned from 1 to 5, based on estimated amount of on-shore land required, duration, and potential conflicts with public projects (lower scores for alternatives with greater land use and potential conflict; higher scores for alternatives with minimal land use and lesser potential conflict). Interrelationships with Other Performance Measures/Timing: This evaluation was conducted in coordination with Performance Measures 3A and 3B. Uncertainty Conditions: At the Feasibility Study level of precision, estimates of land use, duration, and probability of conflicts are limited. However, assumptions and sources of information were summarized and reported. Performance Measure 2F Satisfy Permitting Requirements Target: Satisfy compliance criteria for the Joint Environmental Resource Permit (ERP) and other permits, as necessary. 4/10/2003 engineers & scientists 2-21

42 Metric: Level of anticipated compliance with water and soil quality criteria and impacts on wetlands, threatened and endangered species, lake cross-sectional area, and material reuse requirements. Tool(s): Qualitative tools were used, including information from contractors, vendors, trade publications, the EA pilot dredging project, case studies, and regulatory review, to assess the permitting probability of the various alternatives. Critical Data/Input: Alternatives were defined in scope, schedule, location, and land use in order to successfully estimate the permitting probability. Critical input data were derived from the EA permit, sediment and water quality data, assumed ecological impacts, and applicable pilot study results. Method: Available sediment and water quality data were reviewed to determine the compliance potential of the various alternatives. Following this, a review of ecological criteria (wetlands, benthic impacts, etc.) and archeological criteria (areas of cultural significance) were undertaken. Engineering judgment, data from literature, and discussions with regulatory agencies were used/performed. Scoring: All alternatives were scored based on a qualitative evaluation of permitting probability as described above. Alternative evaluation scores will range from 5 (high permitting probability) to 1 (low permitting probability). Interrelationships with Other Performance Measures/Timing: Alternatives were as narrowly defined as possible. The evaluation was performed after all the modeling, engineering, and environmental analyses were complete. Uncertainty Conditions: Uncertainty in construction equipment performance and duration affect the estimates, as well as the unprecedented scale of a potential phosphorus mitigation project. 4/10/2003 engineers & scientists 2-22

43 GOAL 3: Maximize Cost Effectiveness Performance Measure 3A Minimize Construction Costs Target: Lowest construction cost possible to achieve goals. Metric: The cost in terms of dollars required to construct the alternative, including estimated construction costs and time in years to implement the alternative. Costs presented on a Net Present Value (NPV) basis. Tool(s): Quantitative tools were used that consider information from contractors, vendors, Means cost data, and other construction/equipment/labor cost indices. The pilot dredging project was also considered as a cost estimating source. Critical Data/Input: Alternatives will need to be well defined in scope, duration, location, and land use in order to develop meaningful cost estimates. Uncertainty in construction parameters will significantly affect cost estimates. Method: Costs for alternatives were quantitatively developed and then converted into a NPV parameter. Scoring: Using the range of costs developed for the alternatives, scores were assigned from 1 to 5, based on a relative order of magnitude (1 for the highest cost alternatives and 5 for the lowest cost alternatives). Cost values are also directly reported. Interrelationships with Other Performance Measures/Timing: This evaluation precedes Performance Measures 3B and 3C. Results were considered in 2E and 5C. Uncertainty Conditions: Uncertainty in construction duration affects cost estimations. Equipment/method production rates and number of construction units in concurrent operation are assumed values, based on 4/10/2003 engineers & scientists 2-23

44 best engineering judgment for the alternatives. A +50%/-30% level of accuracy was targeted, and an uncertainty analysis was conducted for the most sensitive cost-related assumptions. Performance Measure 3B Minimize O&M Costs Target: Lowest O&M costs to achieve goals. Metric: NPV cost estimates for a 50-year period of O&M. This includes costs for component replacement, where applicable. Tool(s): Quantitative tools that consider contractor information, experience at other sites, and best engineering judgment, as well as the NPV metric, were used to develop O&M cost estimates. Critical Data/Input: Alternatives were defined in scope, duration, and location in order to develop meaningful O&M cost estimates. Method: The O&M cost estimate incorporates likely post-construction monitoring, reporting, and assumed O&M activities and include anticipated equipment, manpower, and materials. O&M cost estimates were converted to NPV (for a 50-year O&M period). Scoring: Using the range of costs developed for the alternatives, relative scores were assigned from 1 to 5, based on order of magnitude estimates (1 for the highest cost alternatives and 5 for the lowest cost alternatives). Interrelationships with Other Performance Measures/Timing: This evaluation follows Performance Measure 3A (construction costs) and was conducted in coordination with Performance Measure 3C (maximize benefits). Results were considered in 5C. 4/10/2003 engineers & scientists 2-24

45 Uncertainty Conditions: Similar to construction related costs, the O&M costs are subject to uncertainty, as many assumptions were used to develop the O&M cost estimates. A +50%/-30% level of accuracy was targeted and supported by an uncertainty analysis of the most sensitive cost parameter. Performance Measure 3C Maximize Benefits (Material Reuse) Target: Maximize net revenue generated from the beneficial reuse of materials produced during alternative implementation. Metric: Revenue ($) and the timing (start date and duration in years) of the revenue-generating activities. Tool(s): Quantitative and qualitative tools were used, considering estimated volumes (and production costs) of alternative-derived materials and potential market demand/prices for such materials. Critical Data/Input: The alternatives will need to be well defined in terms of the potential volumes of materials produced and the production cost/rate/timing/delivery of such materials. Method: Net revenue was estimated by comparing how much of the cost of an alternative might be offset by revenue generated (if any) through beneficial reuse of materials. Estimates of the potential revenue stream were based on the magnitude and timing of the alternatives, assumed product type, and the production rate and potential marketability of the material. Scoring: Using the range of costs developed for the alternatives and the potential revenue generated by the material reuse sub-alternative, relative scores were assigned from 1 to 5, based on order of magnitude estimates (5 for the highest benefits and 1 for the lowest benefits). 4/10/2003 engineers & scientists 2-25

46 Interrelationships with Other Performance Measures/Timing: This evaluation follows Performance Measure 3A (construction costs) and was conducted in coordination with Performance Measure 3B (O&M costs). Results were considered in Performance Measure 5C (community acceptance). Uncertainty Conditions: Uncertainty in product type, market values, and construction scope and duration affect revenue estimates. GOAL 4: Maximize Environmental Benefits Performance Measure 4A Maximize Benefits to Wetland Vegetation in the Littoral Zone Target: Decrease phosphorus flux into the littoral zone. Metric: Tons of phosphorus transported into the littoral zone (based on long-term model simulations) under the various alternatives. Tool(s): SWAN-LOHTM (see Performance Measures 1A through 1D). Available information on responses of vegetation to changes in phosphorus and TSS flux. Critical Data/Input: Available data on current phosphorus concentrations in the littoral zone, current extent of vegetation, and abundance and diversity of waterfowl and fish. Estimates/descriptions derived from literature of responses of plant community to changes in phosphorus flux. Method: Quantitative estimate based on modeled phosphorus flux to area; qualitatively estimate changes in plant community. Scoring: Higher score means greater decrease in phosphorus and likely improvement in plant community structure. 4/10/2003 engineers & scientists 2-26

47 Interrelationships with Other Performance Measures/Timing: This evaluation was performed after assessments of Performance Measures 1A through 1D were complete. Results considered in 2F, 4E, and 5C. Uncertainty Conditions: See Performance Measures 1A through 1D. Phosphorus and TSS flux to littoral zone were estimated. Clear links between phosphorus and TSS flux and effects on vegetation are not currently available and difficult to identify and predict. Performance Measure 4B Maximize Benefits to SAV Target: 500-meter buffer zone; restoration plan if submerged aquatic vegetation (SAV) destruction cannot be avoided; achievement of k e, critical target set forth in Performance Measure 1C. Metric: Distance between construction zone and existing areas of SAV (to protect existing beds in the short term), and critical light extinction coefficient (to promote SAV expansion in the long term, as described in performance measure 1C). Tool(s): SWAN-LOHTM (see Performance Measures 1A through 1D) and qualitative assessment, as needed. Critical Data/Input: Maps of spatial distribution of SAV. Assumptions regarding spatial scale of alternatives and water column impacts (e.g., resuspension). Method: Desktop comparison of spatial extent of existing SAV to areas likely to be impacted by an alternative to determine if 500-meter buffer zone would be violated during implementation. Evaluation of SAV restoration plan, where necessary. Comparison to Performance Measure 1C target was used to assess long-term impacts. 4/10/2003 engineers & scientists 2-27

48 Scoring: Higher score means a low probability of short-term impacts and high potential for improved conditions in the long term. Interrelationships with Other Performance Measures/Timing: Analysis performed in coordination with Performance Measure 1C. Results considered in 2F, 4D, and 5C analyses. Uncertainty Conditions: Degree of protection offered by 500-meter buffer zone to existing SAV beds. Ability to accurately simulate/predict changes to SAV extent. Uncertainties associated with Performance Measures 1A/1B and 1C. Performance Measure 4C Maximize Benefits to Fish and Aquatic Invertebrate Communities Target: Benefit or improve fish and aquatic invertebrate communities and their habitats in the long term. Avoid short-term disruption or degradation of existing healthy communities and suitable habitats. Metric: Probability for impacts (positive or negative) on habitat quality and, to the extent data or estimates are available, population structure, and composition of important fish and aquatic invertebrate communities. Tool(s): Qualitative assessment based on readily available data and case studies. Critical Data/Input: Results of the latest surveys/studies on existing fish and invertebrate community abundance, diversity, and location; state and location of critical habitat; relevant information from the literature, case studies, and interviews with the FWC. Method: Review of quantitative modeling results; qualitative assessment of impacts on habitat and substrate. 4/10/2003 engineers & scientists 2-28

49 Scoring: Higher score means high probability for enhancement of habitat quality and community composition and structure. Interrelationships with Other Performance Measures/Timing: Evaluate after Performance Measures 1B, 1C, and 1D. Results carried into 2F, 4E, 5A, 5B and 5C. Uncertainty Conditions: See Performance Measures 1B and 1C; lack of relevant, interpreted, site-specific data. Performance Measure 4D Minimize Negative Impacts to the Manatee Target: Increase in desirable native plant forage species (i.e., SAV). Metric: Probability that an alternative would impact (improve or degrade) the manatees habitat or forage areas. Metric will follow metric described in performance measure 4B. Tool(s): Qualitative assessment based on available data and case studies. Critical Data/Input: Locations of forage base; literature review; results of Performance Measure 1B, 1C, and 4B evaluations. Interviews with FWC. Method: Review of quantitative modeling results; qualitative assessment of potential effects on vegetation and manatees. Scoring: Higher scores mean high probability for positive impacts on the habitat and forage requirements. Interrelationships with Other Performance Measures/Timing: Evaluation will follow Performance Measures 1B, 1C, and 4B; findings considered in Performance Measures 2F and 5C. 4/10/2003 engineers & scientists 2-29

50 Uncertainty Conditions: Same considerations associated with Performance Measures 1B, 1C, and 4B; lack of relevant, interpreted, site-specific data. Performance Measure 4E Minimize Negative Impacts to the Alligator Target: Maintain or increase available nesting, juvenile, and adult habitat in the littoral zone. Metric: Measures of the habitat quality include acreage and distribution of Eleocharis marshes and elevated nesting substrate (islands, berms, and tussocks within permanently flooded emergent marsh); pounds/species/acre of invertebrates, and pounds/acre of fish and turtles. Tool(s): Qualitative assessment based on readily available data and case studies. Critical Data/Input: Results of site surveys, to the extent available and interpreted. Method: Qualitative assessment of an alternative s potential to impact or enhance habitat. Scoring: Higher scores mean high probability for enhancement of suitable habitat. Interrelationships with Other Performance Measures/Timing: Evaluation will follow Performance Measures 4C and 5D; findings considered in Performance Measures 2F and 5C. Uncertainty Conditions: Available data from FWC used to estimate potential impacts or benefits. This was an educated and qualitative analysis. Performance Measure 4F Minimize Negative Impacts to the Okeechobee Gourd Target: Increase suitable habitat for the Okeechobee Gourd, and, at a minimum, do not disturb or negatively impact areas known to support the Okeechobee Gourd. 4/10/2003 engineers & scientists 2-30

51 Metric: The number and locations of surveyed Okeechobee Gourd sites located in areas that could be considered for implementing a given alternative. Tool(s): Qualitative assessment based on readily available data and case studies. Critical Data/Input: Available survey results and interpretations by FWC and others. Method: Alternatives evaluated qualitatively for their potential to create or impact known existing critical habitats. Scoring: Higher score (up to 5) means an increase in suitable habitat is likely; alternatives that require actions in near-shore areas, Kreamer, Torry, or Ritta islands, or near the rim canal would be given a low score (1). Interrelationships with Other Performance Measures/Timing: Will follow Performance Measure 5D; findings considered in Performance Measures 2F and 5C. Uncertainty Conditions: Limited data available or interpreted; location of gourd not permanent. Performance Measure 4G Minimize Negative Impacts to the Snail Kite and Wading Birds Target: Improve or have no net impact on the habitat or forage base of the snail kite or wading birds. Metric: Given the number of factors that determine the quality and abundance of habitat and forage base needed to support the snail kite and wading birds, the metric is a qualitative assessment of nesting/nursery and forage quality. Note that apple snails are very dependent on water level and hydroperiod, which cannot be significantly impacted by any sediment management alternative (see performance measure 5D). 4/10/2003 engineers & scientists 2-31

52 Tool(s): Qualitative assessment based on quantitative modeling results and available data and case studies. Critical Data/Input: Results of Performance Measures 1B, 1C, and 4A; existing survey results and interpretations by FWC and others. Method: Qualitative; available data were used to estimate the likelihood of benefits (or impacts) from a given alternative. Scoring: Higher scores mean a high probability of positive effects on critical habitat/forage. Interrelationships with Other Performance Measures/Timing: Evaluation will follow Performance Measures 1B, 1C, 4A, and 5D; findings considered in Performance Measures 2F and 5C. Uncertainty Conditions: Data are limited, links between TSS and phosphorus and impacts to birds are not established; knowledge base is incomplete assessment is limited and highly qualitative in nature as a result. GOAL 5: Maximize Socioeconomic Benefits Performance Measure 5A Maximize Regional Socioeconomic Benefits Target: No effect, or a beneficial effect, on the region s socioeconomic status. Metric: Data on economic activity and employment, to measure changes in the volumes of dollar flows and number of jobs caused by each alternative, will be collected by relevant 2-digit SIC codes. These data will be augmented by retail, commercial, and property tax data from the DOR through the Bureau of Economic and Business Research. 4/10/2003 engineers & scientists 2-32

53 Tool(s): Regional economic activity correlation matrices for were calculated using SPSS software. The matrices provide detail to the zip code level and will be the basis for estimating the effects of sediment management alternatives. Critical Data/Input: Estimates of economic activity using 2-digit SIC codes; monthly retail and commercial sales tax revenues; general spatial description of the economic centers in the region; and employment, equipment, and land use requirements and the physical location of each alternative. Method: Correlation matrices were calculated from the SIC and sales tax data to identify the predominate economic sectors and sector interrelationships by sub-region. The physical requirements of the alternatives were applied to the affected sub-region(s) to estimate (to the extent possible) the resulting effects on the dominant economic activities in the affected zip code areas. Scoring: Relative scores were assigned from 1 to 5 (5 assigned to alternatives with the greatest beneficial impact, 1 assigned to alternatives with the greatest negative impact). Interrelationships with Other Performance Measures/Timing: No direct inputs necessary from any other Performance Measure; however, the output from this Performance Measure is necessary to score Performance Measure 5B and to estimate the probabilities estimated in Performance Measure 5C. Uncertainty Conditions: Some of the input data are estimates, and the projections of future effects are based on the assumption that the interrelationships are represented accurately. To the extent that the estimates and assumptions are incorrect, the estimated future impact may be incorrect. This error will be minimal to a 3-year timeframe, but grows for the projections based on longduration alternatives. 4/10/2003 engineers & scientists 2-33

54 Performance Measure 5B Minimize Environmental/Social Inequities Target: Uniform distribution of economic/environmental impacts. Metric: Economic and employment changes in each geographic sub-region as a result of alternative implementation. Tool(s): Regional economic activity correlation matrices and general spatial descriptions of economic activity developed in Performance Measure 5A. Critical Data/Input: The employment, equipment, and land use requirements and physical location of each alternative; the correlation matrices and spatial descriptions from Performance Measure 5A. Method: The resource requirements for each alternative were defined. These data were used to identify the geographical locations and degree of potential impact. These measures were applied on a zip code basis to determine the burdens borne, both financially and in quality of life, in each area. Scoring: A 5 (high score) was assigned to the alternatives with the most even allocation of impact, and a 1 was assigned to the alternatives that result in the most lopsided allocation of impact. Interrelationships with Other Performance Measures/Timing: This Performance Measure requires the output of Performance Measure 5A and the detailed descriptions of the alternatives. The output from this Performance Measure is necessary to determine the probabilities estimated in Performance Measure 5C. Uncertainty Conditions: Estimates and assumptions carried through from Performance Measure 5A introduce some uncertainty. Use of zip codes to define evaluation areas may mask the presence of unique demographic groups. 4/10/2003 engineers & scientists 2-34

55 Performance Measure 5C Maximize Community Acceptance Target: An alternative with a high probability of community and interagency acceptance along with a low probability of legal challenge is the most desirable outcome. Metric: The estimated degree of public and interagency acceptance, and the potential for legal challenge. Tool(s): Qualitative. Final implementation of the Public and Interagency Outreach Plan (BBL, 2000) and finalization of the stakeholder database were necessary. Critical Data/Input: Feedback received throughout the Feasibility Study; case studies, legal literature, newspaper clippings. Method: Qualitative assessment/comparison. Scoring: Higher score means greater degree of apparent community acceptance and lower probability of legal challenge. Interrelationships with Other Performance Measures/Timing: Performance Measure evaluated as details from all other analyses were necessary to develop the final assessment of probability of community acceptance and legal challenge. Uncertainty Conditions: Important community issues or concerns may not have all been identified. Case studies and legal literature may be subjective, and their applicability may be limited by the potentially precedent-setting scale of many of the proposed alternatives. Performance Measure 5D No Impacts on Water Supply or Lake Operations Target: No adverse effect on water supply or lake operations. 4/10/2003 engineers & scientists 2-35

56 Metric: Lake stage, in feet. Tool(s): Quantitative output from models; most recent versions of relevant plans and reports. Critical Data/Input: Output from models; regulations and requirements in most recent plans and reports. Method: Quantitative comparison of potential impacts an alternative would have on water supply or lake stage against requirements outlined in current plans and regulations. Scoring: Scores assigned on a relative basis, with 5 assigned to alternatives that do not have any impact, and 1 assigned to those with significant adverse impacts. Interrelationships with Other Performance Measures/Timing: This evaluation will follow completion of all the modeling runs and will be conducted in coordination with Performance Measures 2A and 2D. Performance Measures 2F, 4E, 4F, 4G, and 5C were reliant on the results of this evaluation. Uncertainty Conditions: Uncertainty is primarily related to modeling uncertainty. These goals and performance measures for the alternatives are evaluated in the following three sections: Alternative 1 No In-Lake Action (Section 3), Alternative 2 Chemical Treatment (Section 4), and Alternative 3 Dredging with Confined Disposal Facility (Section 5). 4/10/2003 engineers & scientists 2-36

57 3. Alternative 1 No In-Lake Action 3.1 Detailed Description No In-Lake Action This alternative serves as the base case against which methods that employ active management of the sediments are measured. It does not involve any active management of internal phosphorus loading, but instead focuses on evaluating the effects of controlling only external inputs of phosphorus to restore Lake Okeechobee. No mitigation of the sediments would be undertaken to reduce internal loading or attempt to accelerate the rate of recovery once external inputs are reduced. The No In-Lake Action Alternative assumes that the external loading rate of phosphorus (P) will be reduced to a total load of 140 metric tons per year by 2015 in accordance with the TMDL established for the lake. Factoring out inputs of P from atmospheric deposition, this load limit equates to a flowweighted average concentration of 40 µg/l for surface water the target value used in this FS analysis. The phosphorus concentration and external loading reduction schedule assumed in this modeling analysis consists of three parts: 1) Baseline (initial) conditions start in 2000 with an initial concentration of 157 µg/l (equivalent to a load of 426 metric tons). This concentration reflects the average concentration for the previous 10 years. 2) Surface water input concentrations of TP are assumed to decline linearly by 25% between 2000 and 2010 to 118 µg/l (equivalent to a load of 328 metric tons). This reduction is attributed to the implementation of best management practices (BMPs) in the watershed. 3) Between 2010 and 2015, surface water input concentrations are assumed to decline linearly to 40 µg/l (equivalent to a load of 132 metric tons), also as a result of watershed management. A time series plot showing the projected decline of external TP loads is provided on Figure 3-1. A time series plot showing the assumed annual average lake stage used in the model simulations is shown on Figure /10/2003 engineers & scientists 3-1

58 3.2 Evaluation Method Pelagic (Open-water) Zone Effects of the No In-Lake Action Alternative can be separated spatially into two areas of primary concern: effects on the open-water or pelagic zone of the lake, and effects on the near-shore zone where impacts on SAV are of specific interest. This section briefly describes the evaluation methods used to assess the No In-Lake Action Alternative on the pelagic zone of the lake, while the methodology used to evaluate the effects on the near-shore zone is discussed in the following subsection. Evaluation of the No In-Lake Action Alternative method relies upon two modeling tools: 1) the LOWQM (James and Bierman, 1995; Bierman and James, 1995; James et al., 1997; Jin et al., 1998); and 2) the ILPM, developed by Pollman (2000). The LOWQM and ILPM models have both been calibrated to Lake Okeechobee and are used to simulate the long-term effects of external nutrient reduction scenarios on total phosphorus dynamics in the pelagic zone of the lake. Because of the complexity of the nutrient dynamic structure of the model, the LOWQM is used to also simulate changes in nitrogen dynamics, the ratio of TN:TP, and chlorophyll a. The LOWQM also has recently been revised to improve how sediment diagenesis of phosphorus is represented (James et al., in preparation). The advantage to using the ILPM model in conjunction with LOWQM is because both models differ substantially in their structure and how they treat internal loading, a comparison of the simulation results for both models gives some measure of the robustness of the predictions. In addition, the relative simplicity of the structure of the ILPM and the ease with which its code can be modified afforded more flexibility in the types of model analyses that could be explored and conducted. Simulations were conducted for period of 112 years. Since the models are used to project forward in time, hydrologic inputs for each year of the simulation are not known, and can only be estimated. It should be noted that, despite the careful calibration of the models, the predicted simulations of the 4/10/2003 engineers & scientists 3-2

59 response of Lake Okeechobee to various mitigative measures are inherently uncertain. This is due to a number of factors and variables (e.g., hydrology, weather, and climate for any given year in the future) that cannot be known with certainty, although the historical record should provide reasonable estimates of long-term values and year-to-year variations. All these factors can influence the cycling of phosphorus in Lake Okeechobee through changes in hydrologic flushing, sediment resuspension, and biogeochemical activity. Uncertainty in model parameters also contributes to uncertainty in predicted response. For example, the rate of response of Lake Okeechobee to reductions in external loading rates of phosphorus is quite sensitive to the rate at which surficial sediments are removed from contact with the water column via deep burial. One approach to developing hydrologic inputs is to use conditions for the lake (e.g., rainfall volume, lake stage, inflow and outflow rates) averaged across the period of record. Alternatively, one can try to approximate year-to-year hydrologic variations that may occur by using the existing hydrologic record. Because hydrology is very dynamic and near-shore impacts appear to be related in part to changes in lake stage (Havens and Walker, 2002), the latter approach was adopted. Lake hydrology (rainfall depth, inflow and outflow rates, and changes in lake volume) were compiled by year for the available period of record for the lake ( ). This 28-year period of record was then looped in sequence a total of four times to yield a pseudo-hydrologic record of 112 years. A simulation period of this duration proved convenient because it allowed sufficient time for both models to approximate steady-state. Changes in TP surface water inputs to the lake followed the schedule shown on Figure 3-1, while atmospheric deposition of TP directly to the lake surface was held constant. Changes in inflowing concentrations of phosphorus species comprising TP (viz., soluble reactive phosphorus [SRP], total nonlabile P 3 ) and nitrogen species (TN, NH + 4, NO NO - 2 [NO x ], and total organic N) were based the assumption that the ratio of each species relative to TP remains constant during the simulation period. In other words, as TP inputs to the lake were varied according the schedule shown on Figure 3-1, inputs of ancillary phosphorus and nitrogen species were varied in the same manner so that the input ratio of TP:species of interest remained constant throughout the simulation. Changes in inputs of silica 3 Defined as the difference between the total concentration and the dissolved reactive concentration for phosphorus. 4/10/2003 engineers & scientists 3-3

60 (Si) and TSS were calculated in the same manner. Input concentrations for each nutrient species and TSS are shown in Table 3-1. Annual hydrology and total phosphorus loading rates used in the LOWQM and ILPM simulations are presented in Table 3-2. (Note: Hydrology [area, inflow, outflow, and volume latter two variables not shown on Table 3-2] is looped as a 28-year sequence based on observed period of record.) Table 3-1 Nutrient and TSS Concentrations in LOWQM No In-Lake Action Alternative Scenario Year TP (mg/l) TP nonlabile (mg/l) SRP (mg/l) TN (mg/l) TON (mg/l) NO x (mg/l) NH 4 + (mg/l) Si (mg/l) TSS (mg/l) End of Scenario Current Values /10/2003 engineers & scientists 3-4

61 Simulation Year Area (m 2 ) Table 3-2 Loading Rates in Metric Tonnes per Year Inflow (m 3 /yr) Inflow Concentration Reduction Factor Inflow P (mg/m 3 ) Surface Load Atmospheric Load E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E Total Load 4/10/2003 engineers & scientists 3-5

62 The No In-Lake Action Alternative assumes that initial conditions for the scenario reflect conditions observed in Lake Okeechobee during Initial conditions for key parameters in the LOWQM model are shown in Table 3-3. Table 3-3 Summary of Initial Conditions for Key Parameters Used in the LOWQM Model Parameter Atmospheric Load (kg/day) Inflow (mg/l) Water Column (mg/l) Sediment (mg/l) NH 4 + NO 3-1, , Total Inorganic P Available Si ,426.0 Organic N 2, ,022.0 Total Organic P Total Suspended Solids 1,370, Bulk density (0.450 gram [g] dry sediment per cm 3 of total sediment) was computed based on observational data collected by Reddy (1991a) and weighted by areal extent of sediment coverage (Table 3-4, T. James, personal communication). Table 3-4 Sediment Bulk Density for Different Sediment Types Sediment Type Sediment Bulk Density (g/cm 3 ) % Coverage of Lake Mud Peat Sand Littoral Weighted Average 0.45 Data summarized from Reddy (1991a). Critical initial condition inputs for the ILPM are given as follows: 1) Sediment total phosphorus concentration = 1,144 mg/kg dry weight TP (based on average values reported by Reddy [1991] for surficial mud-zone sediments); 4/10/2003 engineers & scientists 3-6

63 2) Porewater dissolved inorganic phosphorus = 199 µg/l; 3) Percent water content of the surficial mud-zone sediments = 85.65%; and 4) The density of the solid sediment particles = 2.15 g/cm Effects on the Near-Shore Region Near-shore effects of the No In-Lake Action Alternative (and other alternatives) were developed using two fundamentally different approaches. First, long-term effects were evaluated using the LOWQM and the ILPM models. Although both models predict changing nutrient dynamics only in the pelagic zone, Havens and Walker (2002) have developed an empirical relationship that allows predictions of annual average near-shore TP concentrations as a function of both annual average TP concentrations in the pelagic zone and annual average lake stage: TP Nearshore = ( *STAGE) * TP Pelagic r 2 =0.071 (1) where TP is the total phosphorus concentration expressed in µg/l and STAGE is the stage elevation for Lake Okeechobee (in feet National Geodetic Vertical Datum [NGVD]). The near-shore TP concentration can then be used to predict the frequency of nuisance algal blooms in the near-shore zone using the following empirical relationships developed by Havens and Walker (2002 ): Freq Chla> C * = 1 Normal( Z * ) (2) Z * = ln( C / GM ) / S (3) GM = TP Nearshore (4) S = TP Nearshore (5) where C * is the criterion defining the occurrence of a bloom (e.g., chlorophyll a = 40 µg/l), Normal is the cumulative standard normal frequency distribution, Z * is the standard normal deviate, GM is the yearly geometric mean chlorophyll a concentration (µg/l), and S is the within-year standard deviation of log-transformed chlorophyll a. For the purposes of this analysis, a bloom criterion of 40 µg/l was 4/10/2003 engineers & scientists 3-7

64 selected. Havens and Walker (2002) define this level of chlorophyll a as indicative of a moderate algal bloom event, and predict blooms to occur with an annual frequency of 2 to 9% when in-lake TP concentrations 40 µg/l. The relationship used to predict the annual likelihood of bloom occurrence using this criterion is shown on Figure 3-3. Short-term effects were predicted using the LOHTM, which was developed explicitly for Lake Okeechobee by Jin and Hamrick (2000) from Hamrick and Wu s (1997) EFDC. LOHTM is a threedimensional, dynamic model that was designed to examine circulation patterns and vertical mixing lakewide. The model has a grid structure of 58 x 66 horizontal cells (each cell is 925 m to a side), with six vertically stretched cells (i.e., each cell is 1/6 of the water depth), yielding a total number of 2,216 active water cells (Jin and Hamrick, 2000). When linked with Delft University s SWAN model, which predicts wind-wave parameters, LOHTM can be used to predict the time- and spatially varying concentrations of TSS in response to changing meteorological and physical conditions in the lake. Once TSS concentrations have been predicted, the associated near-shore impacts of changing TP concentrations and changes in light transparency on submerged aquatic vegetation can be predicted. Based on average data from each of 18 sampling dates, Havens et al. (in preparation) related the standing crop of SAV as a function of both concentrations of TSS and water column depth in the nearshore zone: log SAV = log TSS log Depth Nearshore (6) where SAV is the density of submerged aquatic vegetation (in grams per square meter [g/m 2 ]), TSS is total suspended solids (mg/l), and Depth Near-shore is depth (m) in the near-shore zone. Figure 3-4 shows the predicted TSS concentrations averaged across the near-shore zone on a daily basis predicted by the LOHTM model for the No In-Lake Action Alternative. Also included on the figure is the predicted SAV standing crop based on Equation 6. Equation 6 should be viewed as reflecting a longterm (i.e., weeks) rather than an instantaneous response between SAV and variations in light transmission derived from variations in depth and TSS. In other words, the plots in the middle and 4/10/2003 engineers & scientists 3-8

65 lower panels of Figure 3-4 reflect more properly the potential for changes in SAV community dynamics rather than the actual magnitude of expected response. The LOHTM model also was used to predict short-term impacts of fluxes of particulate P into the near-shore zone. Estimates of changes in particulate P are based on developing a relationship between particulate P and TSS concentrations in the lake. Figure 3-5 is a plot of particulate P concentrations (calculated as the difference between TP and SRP concentrations) versus TSS for all the pelagic stations in Lake Okeechobee between 1972 and Several important features emerge from the plot: 1) The highest particulate P concentrations (expressed as a solid phase concentration normalized to the TSS present) are well over an order of magnitude higher than characteristic sediment concentrations (current average TP concentration in surficial mud-zone sediments is 1,144 mg/kg). 2) The lowest particulate P concentrations in the water column (again expressed as a solid phase concentration normalized to the TSS present) tend to approximate the average TP concentration in the mud-zone sediments of 1,144 mg/kg. 3) The hyperbolic nature of the clustering of the data points suggests that a dilution model comprising two types of TSS sources may explain the data. Conceptually, this dilution model can be postulated as follows: A very thin veneer of recently deposited and highly unconsolidated algae and algal remains overlies the sediment. Alternatively, this veneer can comprise meroplankton, which are planktonic organisms that spend a portion of their life cycle on sediments and are adapted to spending long periods under aphotic conditions. For example, Carrick et al. (1993) found a meroplanktonic assemblage dominated by diatoms (which because of their siliceous tests are more dense than other algal species and sink through the water column far more readily) approximating 5 cm in thickness in Lake Apopka. Assuming that the particulate P concentration of this meroplanktonic layer or sestonic veneer is governed by the Redfield stoichiometric relationship of algal nutrient uptake (Stumm and Morgan, 1996), concentrations of particulate P normalized to the amount of resuspended material should approximate 8,200 milligrams of phosphorus per kilogram (mg P/kg). This floc likely undergoes an almost daily cycle of 4/10/2003 engineers & scientists 3-9

66 resuspension into and settling from the water column. Lying below this easily resuspended floc or meroplanktonic layer is the consolidated sediment. By comparison, this material is greatly depleted in P, averaging approximately 1,144 mg/kg, and is considerably more compacted and dense (average water content approximately 85% to 86%). Because of its higher bulk density, it is resuspended only during more significant wind events. Because of its lower particulate P concentration, progressively higher rates of resuspension of this material (i.e., dilution) would result in progressively lower particulate P concentrations in the water column, normalized to TSS as TSS concentrations increase. The following dilution model was developed to predict how particulate-phase P concentrations, C Particle, would change with TSS. C Particle = C Redfield α α + TSS + C Sediment TSS α + TSS (7) where C Redfield is the expected P concentration for algal material based on the Redfield ratio (8,732 mg P/kg; Stumm and Morgan, 1996), C Sediment is the P concentration associated with consolidated sediment particles (assumed to average 1,000 mg P/kg over the period of record of 1972 to 2001 for available water column TSS and TP data), and α is a fitted concentration ( mg/l) that describes when the mass of TSS in the water column is equally derived from both sediment sources. The coefficient α was fitted using non-linear least squares regression (SAS Institute, Inc. [SAS], 1995). Figure 3-5 shows that the dilution model embodied by Equation 7 (above) reproduces the hyperbolic character of the relationship between particulate P and TSS in the water column. The model, however, underpredicts the normalized particulate P concentration at low TSS, and, rather than presenting a failure of the conceptual model, may reflect luxury uptake of phosphorus by algae beyond the nutritional stoichiometry indicated by the Redfield relationship (i.e., additional uptake of phosphorus beyond the immediate nutritional needs of the organism). The implications that this conceptual model holds for the influence of consolidated sediment entrainment and resuspension on water column TP dynamics are explored on Figure 3-6. These plots show the relative contribution of resuspension of both the overlying meroplankton/seston veneer and the surficial consolidated sediments on total TSS mass in the water and particulate P in the water 4/10/2003 engineers & scientists 3-10

67 column as a function of TSS. The lower panel on Figure 3-6 shows the contributions of consolidated sediment and meroplankton/seston resuspension to the P part burden in the water column. The contributions are weighted by the frequency of occurrence of TSS concentration events between 1972 and 2001 (i.e., how often or frequently TSS equaled a particular value) and assumes that all of the TSS and P part derive from sediment resuspension. These results suggest that consolidated sediment resuspension contributes at most only a minor fraction (17%) to the dynamics of water column TP in Lake Okeechobee, and that resuspension of algal cells and remains as they slowly settle from the water column is more important by a factor of 5 (83%). If this conceptual model is correct, then direct sediment resuspension is less important for internal P recycling than most have previously believed. Indeed, assuming the existence of the hypothesized meroplankton/seston layer and the P part concentrations associated with this material, only a small amount of mass would be required to explain the current TSS-P part relationship in Lake Okeechobee. Across the range of observed TSS concentrations in the lake (1 to 227 mg/l), the dilution model (Equation 7) indicates that the maximum amount of resuspended mass for the algal/seston material and consolidated sediment is 38.5 and g/m 2, respectively. 4 Assuming that this unstable floc consists of 99% water, it would yield a floc thickness of only 0.38 cm. If it were allowed to compact further to yield a water content of 95%, the thickness of the floc would be less than 1 millimeter (mm). Given its comparatively small mass, it is not surprising that this layer has not been previously identified through current sediment-sampling methods. For example, if the algal material were allowed to consolidate to yield an average water content of 85.3% (the average water content of surficial sediments), it would comprise a layer of less than 0.3 mm thick. This thickness is less than 0.3% of the total thickness of the vertically integrated surficial sediment layers sampled by Reddy et al. (2000). 3.3 Uncertainty Impacts and Issues Uncertainty in the phosphorus and associated parameter dynamics predicted for the No In-Lake Action Alternative are related to a number of variables. The first and perhaps most important variable is the 4 Although the period of record includes Hurricane Irene, the observed TSS concentrations may be underpredicted since data have been collected outside of actual storm conditions. Data collected real-time during storm events will help improve the understanding of this relationship and confirm this conceptual model 4/10/2003 engineers & scientists 3-11

68 scheduled reduction in external TP loading rates. This schedule, which was developed by the District (T. James, personal communication), is based on the assumption that nutrient load reductions consistent with the TMDL limit established for the lake will be in place by Since the long-term response of the lake is ultimately governed by the external loading rate, the extent that external loads do not meet the TMDL goal will exert an adverse effect on the lake s recovery. Uncertainty in hydrologic conditions influences residence time and loads to the lake, and this type of uncertainty has been shown to have an important influence on predicted interannual variability of lakewater TP concentrations in the lake (Bierman and James, 1995). By including the 28-year period of record of hydrologic and meteorologic conditions for the lake, the LOWQM, in particular, should be able to reasonably capture the likely interannual variability 5. Although the meteorological record does not include a direct hurricane strike on the lake, Hurricane Irene, which hit in 1999, was close and is part of the record. Further, because the 28-year period of record is looped four times, the impact of a hurricane is considered multiple times in the model results Changes in nitrogen to phosphorus ratios also are uncertain. Since BMPs and stormwater treatment area (STA) assessment has focused principally on phosphorus controls, it is difficult to predict how input ratios of the two nutrients will change with time. Currently, in the absence of more definitive information, we have assumed that TN:TP for Lake Okeechobee inputs will remain constant with time. In reality, denitrification and volatilization of N 2 and NH 3 can lead to greater efficiencies in nitrogen removal compared to phosphorus in wetland treatment areas (e.g., Winchester and Higman, 1987), although comparable removal efficiencies have been observed for both nutrients in natural wetlands in the southeastern United States (Best, 1987). Accordingly, our assumption of similar removal efficiencies appears to be reasonable. Phosphorus dynamics in both the ILPM and the LOWQM models are greatly influenced by sedimentwater fluxes. This uncertainty can affect both the relationship between external loadings and longterm steady-state total phosphorus concentrations, and the time scale during which the lake responds to 5 Because the ILPM does not explicitly include sediment resuspension, the overall variance in TP concentrations predicted by the model is dampened in comparison 4/10/2003 engineers & scientists 3-12

69 changes in external loading rates. Of the two variables, the relationship between external loading and the magnitude of long-term lake response appears to be more robust. This is evidenced by rather good agreement between both models when long-term average water column concentrations are compared for different loading scenarios (Figure 3-7). Bierman and James (1995) noted similar agreement between the LOWQM and the rather simple regression model developed for Lake Okeechobee by Janus et al. (1990). Perhaps most problematic is the inherent uncertainty in the model predictions of the response time of the lake to loading changes and mitigative measures. The temporal dynamics of the response of TP in Lake Okeechobee to changes in the external TP load are governed principally by two phenomena: (1) the hydraulic residence time of the lake, τ w, which averages about 2.75 years; and (2) the residence time of labile or available phosphorus in the surficial sediments. This latter factor is governed both by the rate of net sedimentation (higher rates increase the turnover rate and decrease the residence time of phosphorus in the sediments) and the thickness of the surficial sediment that effectively exchanges solutes with the overlying water column, either through active processes such as sediment resuspension, or through comparatively passive processes such as bioturbation and diffusion. The depth of active exchange for surficial sediments is highly uncertain, and never has been directly measured. Often, phosphorus in sediments as deep as 10 cm below the sediment-water interface is considered to be available for exchange with the overlying water column (Boudreau, 1997). This depth characteristically reflects the ability of benthic infauna to burrow into the sediments, and it is energetically more demanding and less efficient for these organisms to burrow deep into the sediments. Thus, this 10-cm depth represents a depth greater than the depth to which equal mixing throughout the surficial sediment column occurs. It is this latter depth that both the LOWQM and the ILPM models use to simulate sediment-water exchange dynamics. The LOWQM uses two boxes, a surficial box 1 cm deep, coupled with an underlying box 5 cm deep; while the ILPM uses a single 5 cm deep box. Indeed, a number of considerations suggest that active mixing below 5 cm does not occur: 1) The maximum concentration of TSS measured in Lake Okeechobee between 1972 and 2001 is 227 mg/l. Assuming that all of the TSS measured for this event was derived from 4/10/2003 engineers & scientists 3-13

70 resuspension of sediment, and that none of the TSS was associated with algae suspended in the water column, this equates to a resuspension depth of only 0.4 cm. 2) The integrity and shape of 241 Am and 137 Cs vertical profiles measured by Brezonik and Engstrom (1997) in the surficial sediments of Lake Okeechobee indicate that, at a minimum, the bottom sediments have remained intact from sometime prior to 1963 (the peak of activity of the two isotopic markers) to 1988, when the cores were sampled. Based on their results, active mixing appears to be less than 3 cm and could be perhaps less (the sampling interval of the sediments collected at this depth was insufficient to further resolve the change in signal). The effect of the assumed exchange depth on the predicted recovery of Lake Okeechobee was explored using the ILPM model. A model run was conducted where the exchange depth, z, was reduced from 5 to 2.5 cm. Changing z alone, however, results in the model greatly overpredicting the concentrations of sediment P and underpredicting the amount of interstitial P that results from decomposition of organic P in the sediments. This, in turn, produced a lower internal loading flux and lower predicted lakewater TP concentrations. These results were a direct consequence of initially calibrating the model with an organic P decomposition rate, k decomp, that, based on the flux of sediment to the sediment box, and the residence time of that material in the box (which is a function of z), produced appropriate porewater P concentrations and sedimentary P concentrations in the sediment box. To resolve this difficulty, k decomp was doubled. To verify that both model configurations yielded the same steady-state concentration, 10 runs were conducted for inflow concentrations of TP ranging from 40 to 157 µg/l. Figure 3-8 shows that the both model configurations give virtually identical responses at steady-state (t = 120 years). The effect of changing z on the temporal response of Lake Okeechobee to a stepped reduction in external TP loads is shown on Figure 3-9. The simulation was conducted by assuming average hydrologic and morphometric conditions in the lake (e.g., volume, area, and outflow) and by maintaining these conditions throughout the simulation. The simulation was allowed to run for 120 years to ensure that steady-state conditions were reached. Shown in the plot are the relative responses as a function of time. In other words, the fractional degree to which steady-state has been reached, defined as (C t C t=0 )/(C t=120 C t=0 ), is plotted. The time series of this fractional response is 4/10/2003 engineers & scientists 3-14

71 independent of the degree to which the input concentrations have been perturbed; thus, the comparison shows directly the effect of changing the residence time of phosphorus in the sediments embodied by changing z. Also shown on the figure is the response of a conservative constituent such as chloride that is biogeochemically inert. The fractional response of a conservative constituent is governed by the hydraulic residence time, τ w, and it will reach 95% percent of the steady-state concentration within 3 τ w. For Lake Okeechobee, which has an average τ w of 2.75 years, this means that the lake will reach 95% of its new equilibrium concentration within 8.3 years. The time for Lake Okeechobee to reach 95% of its new equilibrium concentration following a change in external TP loadings is 46.2 and 24.7 years for z equal to 5 and 2.5 cm, respectively. In other words, reducing z by 50% reduces the response time by nearly an equivalent amount (approximately 47%). The effects of our uncertainty in z on the predicted changes in lakewater TP for the No In-Lake Action Alternative are shown on Figure As in the analyses presented on Figure 3-8 and Figure 3-9, two model configurations were run for z = 5 and 2.5 cm. Both configurations give the same long-term TP concentration (oscillating about a mean value of 42 µg/l) but, as expected from the results shown on Figure 3-9, the configuration with the shallower exchange depth produces a faster recovery. For example, 20 years into the simulation (2020), TP concentrations in the lake have recovered to 53 µg/l compared to 61 µg/l. Forty years into the simulation, the discrepancy has narrowed (42 µg/l compared to 46 µg/l). Based on this analysis, and coupled with our understanding of the nature and role of wind-driven sediment resuspension on sediment mixing and internal loading, we conclude that our current uncertainty in the sediment mixed layer or exchange depth is more likely to produce a bias toward underpredicting the rate of recovery lakewater TP due to changes in external loading. 3.4 Results of Evaluation No In-Lake Action Pelagic Zone The long-term TP dynamics predicted for the pelagic zone of Lake Okeechobee for the No In-Lake Action Alternative are shown on Figure 3-11 and Figure 3-12 for the ILPM and LOWQM models, respectively. Figure 3-13 compares the simulated results from both models directly. In general, the two models agree rather well, although the LOWQM predicts a greater degree of annual variability. 4/10/2003 engineers & scientists 3-15

72 The greater degree of variability likely reflects the ability of LOWQM to examine directly the effects of wind-driven resuspension on TSS and TP concentrations. The ILPM predicted a somewhat faster initial rate of recovery, although both models predicted very similar long-term TP concentrations. The faster recovery rate predicted by the ILPM is a product of the inability of the model to directly simulate changing wind-driven resuspension effects and capture the larger variability imposed by simulating directly this internal loading source. This would particularly manifest itself as an absolute difference within the first 28-year simulation cycle because of the higher concentration of "legacy" phosphorus remaining in the sediments that predated the beginning of the external load reduction. Nonetheless, because external loads ultimately dictate the magnitude of the source sediment reservoir driving internal loading, the results for the two models converge with time. The ILPM and the LOWQM models predict that Lake Okeechobee will reach 90% of the steady-state concentration (defined here as the average TP concentration for the last 28 years of the simulation period: 42 µg/l and 40 micrograms of phosphorus per liter (µg P/L) for the ILPM and LOWQM models, respectively) by 2033 and 2043, respectively Near-Shore Region The predicted probability of occurrence of a near-shore algal bloom with a chlorophyll a concentration greater than 40 µg/l is shown on Figure 3-11 (ILPM model) and Figure 3-12 (LOWQM model). Based on the ILPM model, the predicted likelihood of occurrence does not drop below 10% until 2028; for the LOWQM, the 10% threshold date does not occur until nearly 30 years later (2057). This discrepancy is a direct result of the greater variance in year-to-year TP concentrations derived from sediment resuspension predicted by the LOWQM. The predicted short-term near-shore TSS concentrations for the No In-Lake Action Alternative simulated by the LOHTM are shown on Figure 3-4. Also shown are the predicted dynamics in SAV standing crop resulting from changes in light transmission induced by the variations in both TSS and depth in the near-shore zone during the simulation period. P part concentrations based on the LOHTM simulated TSS concentrations and the dilution model are shown on Figure The mean concentration (134 µg P/L) is high because the simulation year represents a year of greater sediment 4/10/2003 engineers & scientists 3-16

73 resuspension than normal. For example, pelagic zone concentrations of TSS between 1972 and 2001 averaged 19.8 mg/l, compared to an average near-shore concentration of 51.8 mg/l predicted by LOHTM for the year-long model simulation period Goal 1: Maximize Water Quality Improvements PM 1A: Minimize Time to Achieve Phosphorus Target The target is the amount of time predicted for TP in the pelagic zone of Lake Okeechobee to recover to an average annual average concentration of 40 µg/l. According to the LOWQM predictions, an annual average concentration of 40 µg/l will be reached by 2063, while the ILPM predicts that annual average TP concentrations will reach 40 µg/l by Both models predict relatively stable conditions by approximately The ILPM and the LOWQM models predict that Lake Okeechobee will reach 90% of the steady-state concentration (defined here as the average TP concentration for the last 28 years of the simulation period: 42 µg P/L and 40 µg P/L for the ILPM and LOWQM models, respectively) by 2033 and 2043, respectively. Although the timeframe to achieve the P target could be considered slow in terms of an individual s lifetime, it would not be considered slow for a natural system such as Lake Okeechobee to recover; therefore, this performance measure is given a score of PM 1B: Maximize Reductions in Water Column Phosphorus Concentrations The target goal is an average TP concentration of 40 µg/l. The LOWQM model predicts that the No In-Lake Action Alternative will result in a long-term average (defined here as the average TP concentration for the last 28 years of the simulation period) TP concentration in the lake of 40 milligrams of phosphorus per liter (mg P/L). The ILPM model predicts a slightly higher average (42 mg P/L), but this concentration difference from the target lies within the uncertainty in the model predictions. Although reductions of water column P will take time under the No In-Lake Action scenario, modeling results indicate the target of 40 µg/l would ultimately be achieved; therefore, this performance measure is given a score of 4. 4/10/2003 engineers & scientists 3-17

74 PM 1C: Maximize TSS Reductions in the Short Term and the Long Term The overall target is to reduce turbidity or suspended solids in the near-shore zone of the lake such that sufficient light transparency exists to support an active, viable population of SAV. The original target goal was the critical light extinction coefficient required to support the SAV community in the nearshore zone. To date, this coefficient has not been defined explicitly as a function of TSS; rather, a more direct measure of community activity or viability, viz. SAV standing crop, has been related to water depth and TSS concentrations in the near-shore zone (Equation 6; Havens et al., in preparation). Therefore, this latter relationship was used as the metric for this performance measure. The predicted short-term near-shore TSS concentrations for the No In-Lake Action Alternative simulated by the LOHTM are shown on Figure 3-4. Also shown are the predicted dynamics in SAV standing crop resulting from changes in light transmission induced by the variations in both TSS and depth in the near-shore zone during the simulation period. Predicted TSS concentrations averaged 51.8 mg/l in the near-shore zone, while the predicted SAV standing crop averaged 0.73 g/m 2 ; therefore, this performance measure is given a score of 3 over the short term and a score of 4 over the long term PM 1D: Minimize Algal Blooms The target for this performance measure is to achieve TP concentrations in the pelagic zone < 40 µg/l and to maintain TN:TP > 30. Both the ILPM and the LOWQM models predict that the No In-Lake Action Alternative will essentially achieve a long-term (28-year) average concentration approximating 40 µg/l. The predicted probability of occurrence of a near-shore algal bloom with a chlorophyll a concentration greater than 40 µg/l is shown on Figure 3-11 (ILPM model) and Figure 3-12 (LOWQM model). Based on the ILPM model, the predicted likelihood of occurrence does not drop below 10% until 2028; for the LOWQM, the 10% threshold date does not occur until nearly 30 years later (2057). This discrepancy is a direct result of the greater variance in year-to-year TP concentrations derived from sediment resuspension predicted by the LOWQM, and for that reason, the LOWQM predictions of the rate of recovery are likely more reliable. 4/10/2003 engineers & scientists 3-18

75 This performance measure also considers particulate P (P part ) concentrations based on the LOHTM simulated TSS concentrations and the dilution model shown on Figure The mean concentration (134 µg P/L) is high because the simulation year represents a year of greater sediment resuspension than normal. The No In-Lake Action modeling results indicate that the frequency of algal blooms decreases with time and that the target of below 10% frequency is achieved somewhere during the time period ; therefore, this performance measure is given a score of PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and the Long Term Under the No In-Lake Action scenario, exceedances of FAC Chapter water quality standards are not anticipated in the short or long term as a result of any active or aggressive in lake action. Long-term water quality relative to in-lake P concentrations, which are the focus of this FS, are expected to gradually improve as external load reductions are realized pursuant to the schedule for reductions described in Section 3.1; therefore, this performance measure is given a score of 4 over both the short and long term PM 1F: Minimize Downstream Impacts Under the No In-Lake Action scenario, no active in-lake action would be pursued that could cause a negative impact downstream of the lake. If it is assumed and expected that long-term water quality conditions will improve in the lake based on the reduction schedule for external loads, then, conceivably, downstream receiving water would be expected to improve over time relative to P concentrations (the focus of the FS). This performance measure is given a score of Goal 2: Maximize Engineering Feasibility and Implementability Since no active measures would be performed in the lake under the No In-Lake Action scenario, Goal 2 and the associated performance measures are addressed collectively below. 4/10/2003 engineers & scientists 3-19

76 No In-Lake Action is feasible and implementable. Although this alternative does not include any inlake actions, a robust monitoring program would continue to measure and monitor reductions in external loads. The technologies available for water quality monitoring are readily accessible and relatively advanced. It would be necessary to conduct monitoring in all weather conditions. Sedimentquality monitoring and depth of P exchange information may need to be refined. As long as reductions in external loads could be accomplished by the timetable established and barring any major deviations to the lake-stage management program, it is expected that sediment and water quality conditions would gradually improve and, after 2015, would remain relatively stable. There would be no particular equipment or materials needed other than the monitoring tools and materials required to monitor external loads under a variety of seasonal weather conditions. From the point at which the external load inflow concentration of 40 µg/l is reached (in this case, expected by 2015), water quality conditions are expected to improve, and steady-state conditions are expected to be achieved approximately 30 years later. Based on the results of the modeling, surface sediment quality is also expected to improve as newer, cleaner sediment is deposited over existing sediments. Overall, although no remedy can be expected to be 100% permanent, conditions should remain relatively stable after external load reductions are achieved. There would be no on-shore land use needs or conflicts under the No In-Lake Action scenario and nothing requiring permitting. Unless reductions in external loads occur, however, the reliability and permanence of this alternative are somewhat uncertain. As such, Goal 2 is given an overall score of Goal 3: Maximize Cost-Effectiveness PM 3A: Minimize Construction Costs Other than the costs associated with monitoring stations constructed in the lake (which would be performed regardless of the alternative), there would be no additional construction costs. This performance measure is given a score of 5. 4/10/2003 engineers & scientists 3-20

77 PM 3B: Minimize Operation and Maintenance Costs Other than the monitoring costs associated with water and sediment quality data collection and data evaluation (which would be performed regardless of the alternative), there would be no additional costs associated with the No In-Lake Action scenario. This performance measure is given a score of PM 3C: Maximize Benefits (Material Reuse) There would be no materials considered for reuse under the No In-Lake Action scenario Goal 4: Maximize Environmental Benefits PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone The lake s littoral zone provides critical habitat for waterfowl fish and other organisms. Under the No In-Lake Action Alternative, there would be no impacts due to intrusive activities that would impact wetland vegetation in the littoral zone. The target for this performance measure is to decrease phosphorus in the pelagic zone sediments and thus decrease phosphorus fluxes from resuspended sediment to the littoral zone. Because P part concentrations have been shown to be related to TSS concentrations (Maceina and Soballe, 1990; see also Section 3.2.2), efficacy of an alternative for a mitigation scenario relative to the No In-Lake Action Alternative is based on predicted changes in littoral zone concentrations of TSS derived from the LOHTM. LOHTM simulated TSS and P part concentrations based on the dilution model are shown on Figures 3-4 (top panel) and 3-14, respectively. The mean concentration (134 µg P/L) is high because the simulation year represents a year of greater sediment resuspension than normal. Based on the modeling results, it is anticipated that with time external load reductions would bring about an overall improvement in lake water quality as described in Section All things being equal (i.e., lake stage and exotic species mitigation are managed to support lake ecology to the extent practicable), it is 4/10/2003 engineers & scientists 3-21

78 expected that the overall improvement of water quality would result in improved wetland vegetation in the littoral zone. This performance measure is given a score of PM 4B: Maximize Benefits to SAV SAV plays a critical role in the ecological functioning of Lake Okeechobee as it provides habitat for macroinvertebrates, fish, wading birds, waterfowl, and other wildlife. SAV would not be impacted by any intrusive in lake action under the No In-Lake Action Alternative. As mapped in August 2002 (SFWMD, 2002), SAV covered 43,000 acres of the lake. This compares with a total of 34,800 acres in late summer 2001, when the last SAV map was updated. In addition to a greater overall acreage, the 2002 data indicate an increase in the population of plants that provide good fish habitat, including Hydrilla and peppergrass. Overall, these results may indicate a possible positive response of the SAV community of Lake Okeechobee to the favorable range of water levels that has occurred since fall Water clarity remains good along the shoreline where SAV beds are dense. Shoreline bulrush continues to display signs of stress, particularly due to stem breakage. This is generally believed to be caused primarily by the exotic invasive species rather than by rapidly rising water. To assess favorable light transparency conditions under the No In-Lake Action scenario, short-term concentrations of TSS in the near-shore zone were assessed. In both cases, TSS concentrations were predicted using the LOHTM. The predicted short-term near-shore TSS concentrations for the No In-Lake Action Alternative simulated by the LOHTM are shown on Figure 3-4. Also shown are the predicted dynamics in SAV standing crop resulting from changes in light transmission induced by the variations in both TSS and depth in the near-shore zone during the simulation period. Predicted TSS concentrations averaged 51.8 mg/l in the near-shore zone, while the predicted SAV standing crop averaged 0.73 g/m 2. Based on the modeling results, it is anticipated that, with time, external load reductions will bring about an overall improvement in lake water quality as described in Section All things being 4/10/2003 engineers & scientists 3-22

79 equal (i.e., lake stage and exotic species mitigation are managed to support lake ecology to the extent practicable), it is expected that the overall improvement of water quality would result in improved SAV conditions in the littoral zone. This performance measure is given a score of PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities Invertebrates inhabiting sediments are integral to the Lake Okeechobee food web. The benthic community, especially north of latitude , is a vital food resource to the production and recruitment of important fish species. The recreationally important fish in Lake Okeechobee are the largemouth bass, bluegill, redear, and red and black crappie. Communities and populations of these fish fluctuate every year dependent upon habitat stability. The dominant driver affecting habitat stability is lake stage. Over the last 30 years, there have been annual fluctuations in these fish populations; however, throughout the timeframe from 1972 to present, these fluctuations fall along a relatively flat curve. Based on annual creel surveys performed by the FWC since the 1970s (which is incorporated into FWC annual reports every three years), there does not appear to be an increasing or decreasing trend in fish communities. Creel survey data for black crappie show that, in the 1970s, a commercial program to harvest black crappie almost wiped out the species. These creel survey data also indicate that after the drought in the 1980s the population of black crappie exploded, while during the 1990s, crappie populations decreased due to an absence of vegetation and high water levels. Over the last 20 years, catch rates have generally remained the same for the key recreational species as follows: Largemouth bass are caught on average at a rate of 0.5 to 0.8 fish per hour; Blue gill are caught on average at a rate of 1 fish per hour; Redear are caught on average at a rate of 1 fish per hour, and Black crappie are caught on average at a rate of 2 fish per hour. The commercially important fish in Lake Okeechobee are the bluegill, the redear, and catfish. The annual rise and fall of these populations is also largely a function of habitat stability affected most by 4/10/2003 engineers & scientists 3-23

80 lake stage. It is estimated that commercial fishing yields about a billion pounds of fish per year. There are approximately 10 commercial haulsiene (net) permits in place and approximately three dominant commercial operations. The exotic fish in Lake Okeechobee are primarily the blue tilapia and the armored catfish. These species were introduced via aquarium tank discharges to the lake. Recently, according to the FWC, the blue tilapia population has exploded. The presence of these exotics creates competition with the commercially and recreationally important fish for food and habitat. There is no evidence, however, of an association or relationship between lake-water phosphorous and exotic fish. According to the FWC, phytoplankton blooms occur regularly in the spring and fall along Lake Okeechobee. The presence of phytoplankton blooms has rarely been associated with fish kills or decreased fish populations. There is no indication, according to the FWC, that increases or decreases in lake level P concentrations has any direct cause and effect relationship on fish communities. Rather, as mentioned earlier, the driving factor influencing the fish community is driven by habitat stability, which is impacted as a result of changes in habitat and lake-stage elevation (FWC personal communication, 2002). Based on the modeling results, it is anticipated that with time, external load reductions will bring about an overall improvement in lake water quality as described in Section All things being equal (i.e., lake stage and exotic species mitigation are managed to support lake ecology to the extent practicable), it is expected that the overall improvement of water quality would result in equal or improved fish and aquatic invertebrate communities. This performance measure is given a score of 3 over the short term and a score of 4 over the long term PM 4D: Minimize Negative Impacts to the Manatee Although there is no current population survey data for Lake Okeechobee, the manatee presently finds suitable habitat in the lake. Present SAV levels appear to support an active population (FWC personal 4/10/2003 engineers & scientists 3-24

81 communication, 2002). The manatee would not be negatively impacted by any intrusive in-lake action under the No In-Lake Action Alternative. While the No In-Lake Action Alternative is expected to improve the littoral ecosystem and expand SAV, there is presently no evidence that SAV is a limiting factor for manatees in the lake. The manatee has proven to be very adaptable, surviving on a wide range of vegetation types, and there has been no correlation between lake-water P, TSS, and negative impacts to the manatee (FWC personal communication, 2002). The largest cause of death to the manatee is associated with being struck but boat propellers and getting caught in any of the five locks around the lake. The No In-Lake Action Alternative should perpetuate present conditions that are amenable to the manatee, and is expected to yield improved littoral habitat (and associated SAV). This performance measure is given a rank of 4, as present conditions are suitable for manatees, conditions are expected to improve under this alternative, and no negative impacts are anticipated PM 4E: Minimize Negative Impacts to the Alligator Alligators presently find suitable habitat and trophic resources in the lake. There is no evidence that any conditions related to phosphorus levels are limiting to alligators. Alligators would not be impacted by any intrusive in-lake action under the No In-Lake Action Alternative. According to the FWC, populations of alligators in the littoral zone of Lake Okeechobee are stable or increasing. The overall populations throughout the lake, based on population and nesting surveys performed since 1988, indicate a slight decline; however, the decline is believed to be driven mostly by FWC-managed alligator harvesting programs. Indications are that alligators in Lake Okeechobee are healthy, and there is no indication that the alligators are negatively affected by current P concentrations in the Lake Okeechobee water column. Alligator populations have actually been observed to respond positively to increases in P because, with the increase in chlorophyll a and increase in biomass, there are more rough fish (i.e., shad and perch) 4/10/2003 engineers & scientists 3-25

82 available to this omnivore. Indications are that very eutrophic lakes in Florida tend to host higher alligator populations. The alligators will nest in cattails and torpedo grass, although this exotic vegetation is not as attractive, nor is the nesting success rate as high, as in sawgrass and other emergent vegetation. Based on the modeling results, it is anticipated that with time, external load reductions will bring about an overall improvement in lake water quality as described in Section All things being equal (i.e., lake stage and exotic species mitigation are managed to support lake ecology to the extent practicable), it is expected that the overall improvement of water quality would result in stable or improved conditions for alligators. This performance measure is given a score of PM 4F: Minimize Negative Impacts to the Okeechobee Gourd The Okeechobee Gourd is an endangered vine listed on the Federal Register of July 12, 1993 Clarification, Federal Register, April 1, The Okeechobee Gourd is a fibrous-rooted, highclimbing vine with tendrils. This gourd occurs inside the levee that encircles Lake Okeechobee and sometimes along canal banks south of the lake. Kreamer, Torry, and Ritta Islands and the southern rim canal are the areas currently supporting populations (FDEP personal communication, 2001; USFWS, 2000). The Okeechobee Gourd would not be impacted by any intrusive in lake action under the No In- Lake Action Alternative. The gourd was historically abundant in willow and elderberry thickets surrounded by swamp forest; its primary habitat is presently strongly associated with Torrey muck soils that formed in formerly extensive pond apple forests around the lake By 1930, about 95% of the Lake Okeechobee pond apple forest that had probably been home for this gourd was destroyed for agricultural purposes. At that time, the gourd was still locally abundant, but it has become rare and difficult to find around the lake. 4/10/2003 engineers & scientists 3-26

83 At Lake Okeechobee, there is reason to believe that seeds of this gourd germinate on bare, exposed muck and especially on alligator nests. Pending better understanding of the gourd's autecology, it is appropriate to assume that the species requires periods of low water. Both at Okeechobee and on the St. Johns River, this gourd is associated with alligator nests and nearby willows and elderberries. Since there are no known relationships between in lake P concentrations and the health of the Okeechobee Gourd, no net negative or positive effects are anticipated as a result of the No In-Lake Action Alternative; therefore, this performance measure is given a score of PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds The snail kite, an endangered species, is found in freshwater marshes of the lowlands of southern Florida. Its diet is entirely freshwater snails. The population count for the snail kite in the primary and secondary ranges (Conservation Areas 3A, 2B, Lake Okeechobee, and Lake Kissimmee) was last officially estimated at 1000 in the 1990s. No information on population is available beyond the 1990s (FWC personal communication, 2002). An important area for the snail kite at Lake Okeechobee is Moonshine Bay west of Observation Shoal. There would be no negative impacts to the snail kite under the No In lake Action alternative. Snail kites are resilient, nomadic, and appear to benefit from fluctuations in water levels as long as water levels do not remain too high or too low for prolonged periods of time. They tend to nest in woody areas and prefer to forage in water depths of 12 to 36 inches. Access to the apple snail is of primary importance. Access is most favorable in vegetated areas where the water is clear and the snail kite can see the apple snail within about 3 to 5 inches of the water surface. The snail kite will nest in cattails, although apple snails are difficult for the snail kite to see in cattails, but nest failure is high due to nest collapse (nest collapse is especially high during drought when the cattails become less buoyant). Although cattails do not provide the most favorable habitat for nesting and foraging, destruction of cattail via herbicide application has been observed to negatively impact the snail kite (FWC personal communication, 2002). 4/10/2003 engineers & scientists 3-27

84 Colonies of wading birds such as egrets, storks, herons, woodstorks, and even brown pelicans are robust in the Lake Okeechobee area. Wading bird nesting and foraging can be impacted when water levels are too high or too low (nests are flooded or dewatered and wading is difficult). Although there is no known correlation between in lake P levels and populations of snail kites or aquatic wading birds (FWC personal communication, 2002), both depend on functional littoral habitat. The primary benefits associated with phosphorus management is expected to be enhancement of this habitat. Based on the modeling results, it is anticipated that, with time, external load reductions will bring about an overall improvement in lake water quality as described in Section All things being equal (i.e., lake stage and exotic species mitigation are managed to support lake ecology to the extent practicable), it is expected that the overall improvement of water quality would result in equal or improved conditions for the snail kite and wading birds. This performance measure is given a score of Goal 5: Maximize Socioeconomic Benefits PM 5A: Maximize Regional Socioeconomic Benefits With no in-lake action, the phosphorus loading of Lake Okeechobee is expected to continually improve as a result of attenuation activities upstream from the lake. The lake s phosphorus levels are predicted to reach the target level, a flow-weighted average TP concentration of 40 µg/l by As described in Appendix D, which summaries the Department of Revenue information for zip code areas in the Lake Rim (see Figure D-1 in Appendix D) and SIC codes, the revenue generated by hotels, lodging, and transportation comprises between 0.5 and 1.5 percent of the overall economic activity of the Lake Rim. Therefore, from a strictly economic standpoint (based on reported taxable revenue dollars generated by the Lake Rim), the No In-Lake Action alternative does not affect the economics of the region. Unlike the other alternatives considered, however, there are no direct negative impacts. 4/10/2003 engineers & scientists 3-28

85 To the extent that the reduction of the phosphorus load in the lake makes the water clearer and improves SAV conditions in the littoral zone, the enjoyment derived by those who use the lake recreationally and those who would visit the lake from other areas would be expected to increase. Although no new jobs would be created and no manufacturing plants would be constructed (negative aspects), phosphorus levels in the lake will be reduced to 40 µg/l by 2015, no CDFs would be constructed, and there would be no equipment-related restrictions to the recreational use of Lake Okeechobee. Because there are no direct measurable economic benefits or impacts, this performance measure is given a score of PM 5B: Minimize Environmental/Social Inequities Social inequities are measured by how evenly the positive and negative impacts of an alternative are distributed across the region. As a practical matter, this is best evaluated by the economic and social characteristics of the locations where the alternatives are implemented. As described in Appendix D, evaluating environmental and social inequities across the region is a straightforward task. The economic conditions are strongest on the western half of the Lake Rim, and they weaken toward the eastern rim. Similarly, the economies of the western cities are more evenly distributed across economic sectors than are those of the eastern cities. Ethnically speaking, a large majority of the small number of American Indians in the region live on the northwest rim. Similarly, a large proportion of the sizable African American population in the region lives on the southeastern rim. The equally large population of people of Hispanic cultural heritage is relatively evenly spread throughout the region, with a slightly higher concentration in the east than in the west. Because the phosphorus-containing sediments are generally in the middle of the lake, the distribution of phosphorus in the lake s water is essentially even, and the condition has been in existence for at least 20 years, a slow improvement in the phosphorus levels of the lake will have no greater impact on any one part of the lake than on any other. Environmental and social benefits, as well as economic 4/10/2003 engineers & scientists 3-29

86 opportunities for new uses of the lake, will be uniformly distributed. Therefore this performance measure has been given a score of PM 5C: Maximize Community Acceptance The community of stakeholders and interested parties has expressed concerns that there has been much study and not enough measurable action or improvement in lake water quality over the last 20 years (See outreach meeting minutes, Appendix C). Although the No In-Lake Action modeling results indicate that there should be improvements in water quality and a decrease in frequency of algal blooms by the year 2015, these conditions are heavily predicated on achieving external load reduction targets by Under the No In-Lake Action scenario, progress on watershed P control and management would be very closely scrutinized. The agencies and interested parties would likely expect robust monitoring to verify that external load targets are being met. Also, questions about the science and results of the water quality predictions are to be expected. Modeling would probably have to be repeated as new empirical data become available. While the public and interested parties would not likely object to the absence of additional costs to address internal P, some may suggest that the dollars that might have been spent on in-lake action could be diverted to critical watershed projects to ensure the external targets are achieved. The public may want to see a contingency plan in the event external loads are not achieved at the rate expected. There is always a potential for legal challenges with environmental projects. The expectation is that issues associated with lake stage may, in fact, be more controversial than issues associated with internal P loading since healthy lake habitats are so heavily dependent on a narrow range of water levels in the lake. With continued outreach to stakeholders and interested parties on the matter of future external load reductions and the role of internal P loading, the impetus for legal challenges is expected to be minimized. This, combined with noticeable and measurable improvements in water quality over time, should serve to maximize community acceptance. 4/10/2003 engineers & scientists 3-30

87 Lastly, based on comparisons of the No In-Lake Action scenario with other more active and costly alternatives (which are not entirely effective; see Sections 4, and 5), this performance measure is given a score of PM 5D: No Impacts on Water Supply or Lake Operations Since there would be no in-lake action conducted under this alternative, there would be no expected impacts to water supply or lake operations. Presumably, once external loads are reduced and the frequency of algal blooms decreases, this should result in overall improved water quality for users around the lake; therefore, this performance measure is given a score of 4. 4/10/2003 engineers & scientists 3-31

88 4. Alternative 2 Chemical Treatment 4.1 Detailed Description Chemical Treatment Alum has proven to be a highly effective technique to reduce internal phosphorus loading in both stratified and unstratified lakes, as documented previously (Cooke et al, 1993; Welch and Cooke, 1999). Lake Okeechobee is an unstratified, polymictic lake with no permanent anoxic bottom layer. The characteristics of its sediment make treatment with alum appropriate, especially since the phosphorus-laden mud is relatively shallow and contains relatively low concentrations of phosphorus. 6 Under this alternative, a single application of one or more aluminum compounds (alum, with or without sodium aluminate) would be used to treat lake sediments in place. Sodium aluminate is often added along with alum to ensure proper buffering during application. As long as a ph above 6.0 can be maintained, negative impacts to aquatic life can be avoided. As a method of phosphorus inactivation, the top 10 cm of mud in the pelagic zone would be dosed with aluminum compounds to immediately inactivate mobile phosphorus and the phosphorus that would migrate from lower sediment depths over time by converting the mobile phosphorus to aluminum-bound phosphorus (Al- P). Chemical treatment focused on specific portions of the pelagic zone was considered; however, such an approach was determined to neither yield beneficial results nor adequate reductions in water column P. As a result, the focus of this alternative is the entire pelagic zone. Aluminum sulfate (alum) treatments need to target more than just the phosphorus in the surficial sediment. Examination of sediment cores in lakes previously treated with alum show that phosphorus migrated vertically from deeper sediments and eventually became available for release to overlying water. Often in the past, the calculated dose of alum has not been adequate to account for the quantity of migrating phosphorus that will become available for internal cycling to the overlying water (Rydin et al., 2000). Dose calculations should be more certain in the relatively shallow and definitive Lake Okeechobee sediments, because the potential for underestimating the contribution of migrating 6 It is interesting to note that concentrations of total phosphorus in Lake Okeechobee are not unusually high for Florida lakes. In a study of 97 Florida lakes spanning a broad range of trophic states, the concentration of TP in surficial (top 2 cm) sediments averaged 1,600 mg/kg (Brenner and Binford, 1988) and ranged as high as 8,090 mg/kg. In Lake Okeechobee, the average concentration of TP in the top 1 cm of mud zone sediments is 1,310 mg/kg (data from Engstrom, personal communication), nearly 20% lower than the average reported by Brenner and Binford. 4/10/2003 engineers & scientists 4-1

89 phosphorus is less likely than in other lakes. TP concentration in Lake Okeechobee sediment is about 1 milligram per gram (mg/g); most lakes that have received alum treatments contain more than 2 mg/g (i.e., Campbell Lake, Erie Lake, Long Lake, Pattison Lake, and Wapato Lake, Washington; Mirror Lake, Wisconsin; Dollar Lake, Ohio; Kezae Lake, New Hampshire; Annabessacook Lake, Maine; and others; Welch and Cooke 1999). Another aspect of Lake Okeechobee sediments that justifies detailed analysis of chemical treatment is the relatively low iron to phosphorus (Fe:P) ratio (~ 4:1) (Reddy, 1991b). At ratios less than 10:1, iron does not control phosphorus (Jensen et al., 1992), so there is a relatively large fraction of phosphorus that is mobile even under oxic conditions. Alum addition would be expected to have a greater effect in a shallow, usually oxic lake (such as Lake Okeechobee) in which a large fraction of phosphorus is uncontrolled, than in one where Fe:P is > 10:1. While alum has been a successful and popular treatment to reduce internal loading, lakes have usually been under-dosed. The average longevity of seven well-documented cases was 10.5 years (ranging from just over 4 to more than 13 years) at an average dose of 30 grams alum (as Al) per square meter (g/m 2 ) with a range of 10 to 40 g/m 2 of alum (as Al). As will be seen from the estimates calculated for Lake Okeechobee (discussed in Section 4.1.1), many of these doses were probably too low, since they were estimated by the water alkalinity method (Welch and Cooke, 1999) Methodology (Dose, Application, and Equipment) Alum treatment of lakes has become highly sophisticated. Liquid alum is sprayed onto the lake surface or injected into the lake just below the water surface from a moving barge that is located by a satellite guiding system and equipped with a depth sounder to continuously adjust the flow (and concentration) of alum added, based on changing lake volume. The primary potential problem with applying alum to Lake Okeechobee is its size. Accommodating the lake s large aerial extent would require the application of a large quantity of alum over a long period. The largest water body treated to date is Irondequoit Bay (6.8 square kilometers [km 2 ]) in Lake Ontario; therefore, at approximately 800 km 2, treatment of the pelagic zone in Lake Okeechobee would be a precedent-setting project. 4/10/2003 engineers & scientists 4-2

90 Theoretically, alum could be applied from a plane, as has been the case with liming lakes, but that has not yet been tried. Arriving at the proper dose is extremely important, not so much for toxicity as that should be minimized or eliminated with adequate buffering (see discussion under Goal 4 evaluation, Section 4.4.4) but to ensure inactivation of all mobile phosphorus in the effective sediment layer (here, the top 10 cm), as well as phosphorus vertically migrating up through the sediment column. For many lakes, an optimum dose that would convert all mobile phosphorus (i.e., the phosphorus in the effective layer and the vertically migrating phosphorus) to Al-P has been suggested as 100 times the mobile phosphorus content in the upper 4-cm depth of sediment (Rydin and Welch, 1998; Rydin and Welch, 1999). The alum dose for Lake Okeechobee was estimated by three methods: mobile phosphorus, internal loading, and exchangeable phosphorus. For mobile phosphorus, a 10-cm sediment depth was chosen, along with an aluminum to aluminum-bound phosphorus (Al:Al-P) formed ratio of 10:1 observed in several Washington lakes (see Rydin et al., 2000) and a sediment dry weight of 0.2 g/cm 3. An Al:Al-P ratio of 10:1 was used for Lake Okeechobee instead of the 100:1 from Rydin and Welch (1999) because of Lake Okeechobee s shallower total sediment depth and thicker sediment layer (10 cm vs. 4 cm). This represents a factor of 2.5 increase in dose due to the deeper sediment layer used in calculations. Further assumptions are a treated area (i.e., mud zone) of 80,000 ha, with a mean water column depth of 4 m. Mobile phosphorus (iron-bound phosphorus and loosely sorbed phosphorus) has not been determined for Lake Okeechobee sediments, but non-apatite inorganic phosphorus (NAIP) values are available from Pollman (1991; mg/g), Brezonik and Engstrom (1998; mg/g), and Reddy (1991a; mg/g) as averages in the top 10 cm. In lieu of data on mobile phosphorus, NAIP was used to estimate dose. Use of NAIP instead of mobile phosphorus also justifies use of a 10:1 Al:Al-P ratio instead of a 100:1 ratio. Mobile phosphorus can be expected to be considerably less than NAIP, as was the case in a Wisconsin lake where mobile phosphorus was half the NAIP value (Rydin and Welch, 1999). Alum (as Al) dose estimates based on the three NAIP values for Lake Okeechobee are 6.6 g/m 2, 113 g/m 2, and 99 g/m 2, respectively. By comparison, dose estimates for 4/10/2003 engineers & scientists 4-3

91 three Wisconsin lakes were 150 g/m 2, 90 g/m 2, and 80 g/m 2 alum (as Al) using mobile phosphorus (Rydin and Welch, 1999). There are two estimates of internal loading: 24 milligrams phosphorus per square meter per year (mgp/m 2 -year) and 1.7 mgp/m 2 -day, extrapolated to 300 mg/m 2 -year and 600 mg/m 2 -year for one-half and one full year, respectively. These produce alum (as Al) dose estimates of 3.6 g/m 2, 45 g/m 2, and 90 g/m 2, respectively. Exchangeable phosphorus values of unit of measurement to unit of measurement produce alum (as Al) dose estimates from 4.8 g/m 2 to 132 g/m 2. To better ensure treatment success, the higher estimates from each of these three methods produce a alum (as Al) dose estimate of around 100 g/m 2 for Lake Okeechobee. With a mean depth of 4 m, the resulting concentration alum (as Al) dose to the water column is 25 g/m 3. Up to eight application barges could be used to add the alum to the pelagic zone of Lake Okeechobee. Each barge could apply alum at a rate of 50,000 gallons per day (gpd) to 100,000 gpd or 22,200 kilograms alum (as Al) per day. Operating at 260 days per year for 8 hours per day, it would take 21 months or just under 2 years to complete the treatment. The distribution of materials into the lake would be controlled by a computer that continually monitors the water depth and boat speed and automatically adjusts the valves to deliver a precise dose of materials to the water. The alum would be applied to the surface or injected below the surface. A computerized satellite navigational system would be available to guide the operator back and forth across the lake in parallel paths. This would provide for accurate, no-skip, no-overlap coverage and would potentially eliminate the need to drop and retrieve buoys to mark the paths Shipment and Transport of Materials to the Site There are five production facilities for alum in Georgia and three in Florida. Alum and sodium aluminate can be shipped either by rail or truck. If shipped by rail, the alum could be transferred to trucks for delivery to the staging site. The materials would then be transferred directly to the application barges by employing a small pump and hose system. The barges would be brought to the 4/10/2003 engineers & scientists 4-4

92 site by truck and trailer and placed in the lake with a crane. Potential suppliers have suggested they would consider constructing an aluminum processing facility near the lake to reduce shipping costs and serve other clients. This would not be required, but it would be an option for the supplier, who could either have the alum shipped to the site or produce it nearby. In either case, the final delivery would be by tanker truck to the lakeshore. Beside access to the lakeshore, the only other requirement for the area is that it be bermed as a precaution against potential spillage of materials Land-use Needs (Staging of Equipment and Materials, and Production Facility) Part of the success of the alum treatment of lakes has come from the relative ease with which alum can be applied to the lake environment. Existing public access areas have served as staging areas for most other alum treatments. The specific needs for a staging area for an alum treatment for Lake Okeechobee are: A maximum area of 2 to 5 acres on the lakeshore per access area; An access road to the staging area that would support commercial tanker truck transport and wide-load vehicles that deliver barges and alum materials; and Temporary dock(s) or platforms to which barges could be tied for cleaning and maintenance. (Note that the application barges would require little maintenance other than routine maintenance on the drive motor and material pumps.) Permanent dock facilities are not required for material transfer. In addition: Alum and sodium aluminate would be stored in the tanks used to deliver the material until use. The immediate area around the tanker trucks would be required to be bermed for spill protection, but this has not been a requirement in other applications because the material has been transferred via pump directly into the treatment barges. Multiple staging areas located at different access points along the lake would increase the efficiency of alum treatment by reducing the water travel time. 4/10/2003 engineers & scientists 4-5

93 If a processing facility were to be constructed, it would be the material supplier s choice to do so for long-term market expansion and would not necessarily be a direct outcome or requirement for this treatment. If a plant were constructed, it would take 9 months to construct after permits and land were acquired. This would not delay the alum application because the treatment materials could be shipped to the site from outside sources Duration of Alternative (Staging, Implementation, Post-Implementation) Staging Everything needed to perform the alum treatment is commonly available and would not require specific manufacturing or tooling; therefore, only a 30-day planning and mobilization period is necessary to start the project Implementation The in-lake barges would be supplied with alum and sodium aluminate from tanker trucks or a large barge located near the active treatment site within the pelagic zone of Lake Okeechobee. The distribution of alum and any buffer into the lake would be controlled by a computer that continually monitors the water depth and boat speed and automatically adjusts the pump/valve system to deliver a precise dose of materials (25 grams per cubic meter [g/m 3 ]) to the water. Liquid alum and liquid sodium aluminate would be applied to just below the water surface. A computerized satellite navigational system coupled with on board GIS would allow for even distribution of alum over the sediment surface Post-Implementation Long-term monitoring of the lake for response to the alum treatment and long-term tracking of any indirect changes in the lake s ecosystem would be necessary after the treatment. This monitoring should include limnological parameters and studies of the biological communities. Monthly 4/10/2003 engineers & scientists 4-6

94 monitoring would need to start 1 year prior to the treatment and continue for 20 years, or until the lake s phosphorus concentration attains equilibrium. Because there would be limited impact associated with the staging area if either pre-existing access areas are used or if staging areas have to be constructed, the decommissioning would be limited to cleanup and re-vegetating the near-shore areas where tanker trucks parked. Additional work may be required if an access road is constructed and must be decommissioned Data Needs A pilot study would be necessary to demonstrate the environmental benefits and impacts to the benthic and fisheries community. This study would require 18 months to plan, implement, and conduct preand post-monitoring and analysis. A pilot study would include the treatment of at least 100 ha of the target area by alum. Studies would include sediment testing, benthic invertebrate community analysis, fisheries analysis, and limnological studies. During the development of bid documents, additional data would need to be collected to verify the alum dose. Activities would include sediment sampling and determination of the mobile-p concentration, as discussed in Section In addition, alum flocculation tests would need to be performed to define application operational protocols. Testing would require 60 days to perform and conclude; it would not add to the time required to produce the construction documents. It is standard industry practice for sodium aluminate to be added to the lake in a 1:2 volume ratio to alum. This means that, for every half-gallon of sodium aluminate applied to the lake, a gallon of liquid alum would be applied. To verify that this is the correct application ratio for the Lake Okeechobee alum treatment, this application ratio would be tested ahead of time using jar tests. The purpose of adding sodium aluminate is to maintain a ph above 6.0 to avoid potential impacts to aquatic life. The portion of aluminum from sodium aluminate would be increased in batch tests in order to maintain the ph level above /10/2003 engineers & scientists 4-7

95 4.1.6 Summary Dose Alum dose should be 100 g alum (as Al)/m 2 Resulting concentration dose to water column 25 g alum (as Al)/m 3 Equipment 1 production facility may be built near the shore of the lake to supply necessary alum. If no facility is built, rail, barge, or truck access would be necessary. 8 barges would be used to apply alum to the lake s pelagic zone Duration Staging: 30 days after environmental documentation and permitting (which is expected to take approximately 8 years) Implementation: 2 years, including staging Post-implementation: 20 years 4.2 Evaluation Method ILPM Model Simulations In conducting simulations of the predicted effects of alum addition with the ILPM and the LOWQM models, two key assumptions were made: 1) Chemical treatment with sodium aluminate binds soluble inorganic phosphorus in the porewater; the bound P is inert and essentially permanently lost to the system. 2) The total efficacy of the treatment is to reduce the internal load by 80%. (See additional discussion under Performance Measure 1A: Maximize Water Quality Improvements.) Over the long term, this efficacy would reflect both binding by the alum and the reduction in the organic load of P delivered to the sediments, which, in turn, reduces the amount of dissolved inorganic P in the porewater derived from decomposing organic P. A pathway for removing a fraction of the 4/10/2003 engineers & scientists 4-8

96 mineralized P as it is being produced in the surficial sediments was introduced into the ILPM model to reflect alum binding. Fluxes in toto of soluble inorganic P derived from mineralizing sedimentary P are not affected; rather, just the amount that is introduced into the porewater and remains available for exchange across the sediment-water interface. In the ILPM model, the production rate of dissolved inorganic phosphorus due to mineralization of sedimentary P is calculated as a first-order decay reaction: J decomp = k decomp P sed (1) where J decomp is the production rate of dissolved inorganic phosphorus (mg P/kg sed-yr), k decomp is the first order organic P mineralization coefficient (1/yr), and P sed is the sediment P concentration 7. The sequestration of the mineralizing P due to introduction of alum was simulated using a binding fraction coefficient, β alum : J alum = β alum k decomp P sed (2) where J alum is the sequestration rate of mineralized P due to the alum addition (mg P/kg sed-yr), and β alum is a fraction that can range in value from 0 (no sequestration) to 1 (complete sequestration). Thus, the net flux of mineralized P, J net, into the porewater is given by combining equations 1 and 2: J net = (1 β alum ) k decomp P sed (3) Initial testing of the model demonstrated that the requisite value of β alum to reduce the internal loading flux predicted by the ILPM by 80% under steady state conditions varied with the influent TP concentrations of the external load. As a result, a series of 13 long-term simulations (120 years) were conducted to define β alum across the expected range of influent TP concentrations (157 to 40 µg/l), and a cubic equation was fitted to the results to describe the resultant relationship: 7 Unlike LOWQM, the ILPM model does not differentiate sedimentary P into different fractions. 4/10/2003 engineers & scientists 4-9

97 β alum = P in P in P in 3 (4) where P in is the flow-weighted inflow concentration of TP for surface water inputs to Lake Okeechobee (excluding precipitation). See Figure 4-1. Equation 4 was then coded into the ILPM to produce changes in β alum with changing P in. Simulations for the Chemical Treatment Alternative assumed the following schedule: Construction of the facilities to produce the alum would be completed by Dosing the lake would begin in 2012 and would be completed by the end of At that point, full efficacy (i.e., 100%) of the alum treatment would be expected. It was then assumed that the efficacy of sequestering the mineralized inorganic P in the sediments remains constant for 8 years, then drops to 0% efficacy in a linear manner over the next 7 years. Effective β alum values based on this schedule are shown on Figure LOWQM Simulations Simulations of the expected benefits derived from the Chemical Treatment Alternative using the LOWQM were conducted somewhat differently than with the ILPM model. The primary difference was the manner in which alum binding was treated in the model. Because of the complexities in the model, the project team deemed that the most appropriate manner to represent alum binding of porewater dissolved inorganic phosphorus was to adjust the linear partition coefficient that dictates the equilibrium established between the aqueous and particulate (sorbed) phases in the porewater: P sorbed = K d P porewater (5) where P sorbed is the concentration of sorbed, readily exchangeable P on the sediment particles (mg P/kg sediment), P porewater is the concentration of dissolved inorganic P in the porewater (mg P/L), and K d is the linear partition coefficient (liters per kilogram [L/kg] sediment). By increasing K d according to the dosing schedule of alum described earlier, P porewater is reduced, and internal loading derived from 4/10/2003 engineers & scientists 4-10

98 passive sediment-water exchange processes (e.g., processes other than direct sediment particle resuspension) are reduced. Upon dosing the lake with alum, K d then was allowed to decline to reflect its diminished efficacy in further binding P porewater due to both removal of alum from the sediments because of deep burial and saturation of its sorption capacity (Figure 4-2). One critical difference between the ILPM and LOWQM is the fate of the pool of alum-sequestered P in the sediments once alum efficacy begins to decline. In the ILPM, this pool is permanently fixed or sequestered and, thus, effectively removed from the system. As a result, the ILPM model predicts that Lake Okeechobee would slowly return to the time series trajectory of P concentrations defined by the No In-Lake Action Alternative. This is illustrated on Figure 4-3, which shows that lakewater TP concentrations during the period of full alum efficacy will decline to approximately 25 µg/l, and that the time trajectories for the two alternatives will not converge until approximately 2060, when both alternatives predict lakewater TP concentrations approximating 40 µg/l. As indicated by Equation (5), LOWQM predicts that the pool of exchangeable P increases during the period of full alum efficacy. Unlike in the ILPM model, this pool is not permanently sequestered in the LOWQM model, and will re-equilibrate with P porewater to establish a new equilibrium as the efficacy of the treatment (and hence K d ) begins to decline. To more properly simulate the long-term sequestration of alum and preclude the release of P fixed by alum as the alum sorption capacity becomes exhausted, K d values were slowly reduced beyond The rate of decline in K d was calculated as function of the removal of alum-fixed P from the surficial sediments by deep burial. The LOWQM predictions comparing TP concentration for the No In-Lake Action and Chemical Treatment alternatives are depicted on Figure Uncertainty Impacts and Issues Uncertainty in the efficacy of alum as a means to mitigate the flux of phosphorus from the sediments to the water column and thus promote a faster rate of recovery in Lake Okeechobee stem from several possible sources: 4/10/2003 engineers & scientists 4-11

99 1) Is the magnitude of internal loading due to the release of soluble phosphorus from the sediments in the water column reasonably well understood? 2) Would alum be effective in sequestering the release of this phosphorus? 3) Do the ILPM and LOWQM models reasonably reflect the ability of alum to immobilize phosphorus in the sediments and prevent its export back into the water column? 4) How would the lake be affected by chemical treatment in the absence of external load reductions over time? These issues are discussed below. 1) There is little doubt that internal loading is important several lines of evidence support the notion that it is. The question is how well can we estimate the magnitude of this loading. Porewater equilibrator data clearly show that a strong concentration gradient develops in the surficial sediments, and diagenetic modeling based on these gradients indicate that this flux approximates 0.6 mg/m 2 -day (Pollman, unpublished manuscript), compared to a long-term external P loading rate of ca. 1.8 mg/m 2 - day. In reality, the porewater data suggest that benthic infauna or wind-driven mixing promote very rapid exchange of dissolved phosphorus between the surficial 4 cm of the sediments and the water column, and a higher rate of supply (due to a very sharp concentration gradient) than the model estimated. Laboratory studies using intact cores from the lake (Moore et al., 1998; Fisher et al., in review) also indicate that the internal P loading rate is higher, and range from 1.0 to 1.7 mg/m 2 -day. Because the intact core studies cannot reproduce the effects of wind-driven disturbance of the sediment-water interface, these reported fluxes likely are lower than the actual rates occurring in the lake. 2) With respect to the question of the efficacy of alum treatment, one of the advantages of using alum is that the method has an extensive history of application to other lakes, and, as a result, calculating appropriate dosing levels has become more precise and accurate. Dosing calculations for Lake Okeechobee (see Section 4.1.1) were based on several different methods: mobile phosphorus, internal loading, and exchangeable phosphorus. To better ensure treatment success, the higher estimates from each of these three methods were used to produce a final alum (as Al) dose estimate of around 100 4/10/2003 engineers & scientists 4-12

100 g/m 2 for Lake Okeechobee. The possible efficacy of alum is also supported by the relatively low iron to phosphorus (Fe:P) ratio (~ 4:1) (Reddy, 1991b). Below ratios equal to 10:1, iron does not control phosphorus (Jensen et al., 1992); thus we expect that a relatively large fraction of phosphorus in the surficial sediments and porewater is mobile even under oxic conditions. Indeed, alum addition is expected to exert a greater effect in a shallow, usually oxic lake (such as Lake Okeechobee) in which a large fraction of phosphorus is uncontrolled, than in a lake where Fe:P is > 10:1. 3) With respect to the ability of the LOWQM and the ILPM models to simulate the ability of alum to sequester phosphorus in the surficial sediments ultimately, this is a question that must be resolved by conducting laboratory and mesocosm-level experiments. Both models simulate the effect of alum by reducing the internal P loading flux by ca. 80% based on field observations. Since the models treat internal loading differently, somewhat different results are obtained regarding the absolute magnitude and duration of the reduction in lakewater TP concentrations owing to alum addition (see Sections 4.2 and Figure 4-5). Because LOWQM does not treat P sequestration by alum as a permanent process, it likely underpredicts the duration of the enhanced reductions in lakewater TP owing to the treatment. For example, the LOWQM simulation shown in Figure 4-4 would suggest that, beyond 2047, the residual alum-bound P pool in the sediments releases sufficient P into the water column to result in concentrations slightly higher than would occur under the No In-Lake Action Alternative. This result is an artifact of how the phosphorus distribution coefficient, K d, was estimated to change with time beyond the initial period of full efficacy. The ILPM model, in turn, may overpredict the magnitude of the alum effectiveness because it makes no distinction between internal loading due to soluble P exchange across the sediment-water interface, and P resuspension into the water column due to windwave activity (see Figure 4-3). Thus it seems very likely the best prediction of the long-term efficacy of alum treatment lies between the trajectories predicted by each of the two models shown in Figure ) Finally, to assess what would happen if lake TP concentrations remain as they are today (about 157 µg/l averaged over the last 10 years), an evaluation was performed. Figure 4-6 compares predicted pelagic lakewater TP concentrations with and without chemical treatment under conditions of a constant surface water input concentration of 157 µg/l. Two possible scenarios of chemical treatment 4/10/2003 engineers & scientists 4-13

101 are compared: (1) Single whole-lake dosing (i.e., the Chemical Treatment Alternative) with dosing beginning in 2013; and (2) multiple dosings with alum on a 17-year cycle. The 17-year cycle reflects two years to complete the dosing, 8 years of full efficacy, and a following period of 7 years of linearly declining efficacy. The performance measure specific analyses for the Chemical Treatment Alternative are discussed below. 4.4 Results of Evaluation Chemical Treatment Goal 1: Maximize Water Quality Improvements The effectiveness of the alum treatment would be expected to be 80% initially and to last approximately 15 years. However, incoming solids and phosphorus from external sources, as well as the wave-induced resuspension and mixing of existing sediments, may diminish the performance of this alternative over the 15-year period. Thus, this alternative may be effective in the short term, but become less reliable over the long term, depending on the degree of disruption from wave-induced resuspension. To predict lake response, effectiveness is assumed to hold at 80% for 8 years and then decline linearly to zero effectiveness over the remaining 7 years. The 80% effectiveness and longevity estimate is based on well-documented cases. In two shallow lakes in Washington, effectiveness was initially 80% and 60%, held rather constant for several years, and then declined to 40% and 35% after 8 years. A stratified lake in Wisconsin showed 95% effectiveness initially and was still 80% effective after 13 years (Welch and Cooke, 1999) PM 1A: Minimize Time to Achieve Phosphorus Target An alum treatment of the lake would result in achieving the in-lake phosphorus target of 40 µg/l by the end of the treatment period 2015 (Figures 4-3 and 4-4). The ILPM model (Figure 4-3) clearly shows that alum would control in-lake P concentration to 40 µg/l or less until The same model predicts that it would take the lake until 2080 to approach in-lake phosphorus concentration of 40 µg/l with the No In-Lake Action Alternative. An added benefit of alum treatment is that the target P 4/10/2003 engineers & scientists 4-14

102 concentration could be met and maintained until the impacts of external watershed measures controlling P loading to the lake have taken effect (Figures 4-3 and 4-4). Alum treatment of the lake results in significantly faster recovery of the lake in terms of P concentration and, in turn, lowered algal production. The results from the LOWQM also suggest that alum treatment would significantly reduce the time necessary for Lake Okeechobee to respond to reductions in external P inputs (Figure 4-4), although when compared to ILPM results, the magnitude of the response is comparatively less (Figure 4-5). The more muted response predicted by the LOWQM likely reflects how the two models treat internal loading processes in the lake. LOWQM considers passive diffusion and sediment resuspension as two separate processes, and values of K d were selected to reduce the flux from the passive diffusion pathway by 80%. ILPM does not distinguish between both phenomena and lumps passive diffusion and sediment resuspension together as a single release pathway. Values of β alum were selected to reduce this combined internal load flux by 80%. Thus, the ILPM predictions may reflect a systematic bias towards an overestimation of efficacy 8. Since LOWQM treats sequestration as an exchangeable rather than a fixed process, it may represent a systematic bias towards underestimating the long-term benefits of alum. Thus, it seems very likely the best prediction of the long-term efficacy of alum treatment lies between the two trajectories shown in Figure 4-5. This performance measure has been given a score of PM 1B: Maximize Reductions in Water Column Phosphorus Concentrations Both the ILPM and LOWQM model predict a rapid decline in in-lake P concentrations (Figure 4-5) to below or near 40 µg/l when the lake is treated with alum, as compared to the No In-Lake Action Alternative, which would take until approximately 2080 to approach the goal of 40 µg/l. With an alum treatment, the lake s P concentration would meet the 40 µg/l goal by the year Alum treatment increases the certainty that in-lake P concentrations would meet the phosphorus goal. Therefore, this performance measure has been given a score of 4. 8 That the ILPM predictions indeed represent a systematic bias towards overpredicting efficacy because of how internal loading is represented in the model is by no means certain. Alum reintroduced into the water column by wind-induced resuspension likely will contribute to further removal of P from the water column a process that ILPM cannot simulate. 4/10/2003 engineers & scientists 4-15

103 PM 1C: Maximize TSS Reductions in the Short Term and Long Term An alum treatment of the lake would increase transparency of the lake by reducing P availability and, hence, reduce algal blooms. In addition, alum treatments typically result in an immediate improvement in water transparency because the alum floc removes particulate from the water column as it settles to the bottom of the lake (Cooke et al., 1993). In most lakes that have been treated with alum, the aquatic macrophytes have responded to the increase in available light with production increases in both density and coverage. This would also be expected to occur in Lake Okeechobee. The increase in transparency and decrease in suspended solids resulting from the alum treatment would provide an opportunity for submerged aquatic macrophytes to increase their rate of photosynthesis and, hence, aerial expansion. Alum may not directly impact the resuspension of bottom sediments due to wind energy. It would, however, increase the rate of settling because of increased density and settling characteristics of the alum floc. The net impact would be that the alum treatment would result in TSS reduction in the lake and an overall improvement in water quality. Therefore, this performance measure has been given a score of 4 over both the short and long term PM 1D: Minimize Algal Blooms Based on the modeling performed, alum treatment would reduce the available P concentration in Lake Okeechobee; the TN:TP ratio would be increased to more than 30, and the absolute amount of P would be reduced to 40 µg/l (Figures 4-3 and 4-5). This would limit algal production and reduce the annual occurrence of blue-green algal blooms, as is illustrated by the results of the models presented on Figures 4-7 through These model results basically predict that the annual probability of algal bloom occurrence is reduced to 5% when an alum treatment is applied to the lake to control P concentrations. This is substantially reduced from the No In-Lake Action Alternative and is the direct result of reducing internal cycling of P. Therefore, this performance measure has been given a score of 4. 4/10/2003 engineers & scientists 4-16

104 PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and Long Term Water quality standards in the lake pursuant to FDEP Chapter are not likely to be exceeded with an alum treatment. The addition of alum to the water column with a buffer, such as sodium aluminate, would result in no net increase in the aluminum concentration (as either soluble or total aluminum) in the water column (Cooke et al. 1993). Upon addition to the water column, the aluminum immediately hydrates, forming an aluminum-hydroxide polymer that is insoluble. This polymer would form a floc that would settle to the sediment surface within minutes of the alum addition to the water column. There is a short-term increase in the concentration of sulfate in the water with the addition of alum, but this has not resulted in water quality exceedances in other alum applications, including water-supply treatment (Welch and Cooke 1999). There is some degree of uncertainty associated with the potential for methylation of mercury in the lake due to increase in sulfate, and, although this is not anticipated to be significant, further evaluation should be performed. This performance measure has been given a score of 3 for short-term concerns, and 4 over the long term PM 1F: Minimize Downstream Impacts By rapidly reducing the available P concentration in Lake Okeechobee to 40 µg/l, the increase in TN:TP ratio would limit algal production and reduce the occurrence of blue-green algal blooms, which would result in improved water quality of the lake and its outflow water. Given that P is the key to controlling the water quality of Lake Okeechobee and that alum would quickly result in achievement of target P concentrations in the lake, the downstream water quality would likely benefit, as well. In turn, ecological benefits would follow. There is nothing to indicate that alum would have impacts on the lake s downstream water quality. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of Goal 2: Maximize Engineering Feasibility and Implementability Alum treatment of lakes has been successful since first implemented in 1974, and its use in Lake Okeechobee is both feasible and implementable. Welch and Cooke (1999) have documented the use of 4/10/2003 engineers & scientists 4-17

105 alum, its effectiveness, and performance risks. If the proper dose is used, P would be controlled to meet the restoration target of 40 µg/l. Although there is no reference case study to demonstrate the ability to scale up to an application comparable to the one envisioned for Lake Okeechobee, from a technological point of view, there is no physical or chemical condition that prevents the treatment of the lake. The equipment and labor skill readily exist and could be easily adapted for this specific action PM 2A: Maximize Technical Reliability Once the application of alum is complete, there are no O&M actions or costs. The treatment process itself is conducted with standard equipment, barges, motors, small-volume gasoline pumps, and laptop computers that require normal maintenance, but no specific or specialized maintenance. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 2B: Maximize Technical Scalability Although there has not been an alum treatment of the magnitude proposed for Lake Okeechobee, alum treatments have been scaled up successfully from small applications to significantly larger applications. Cooke and Welch (1999) have documented the risk and successes of reported alum treatments, and it is clear from their work that scale-up is not a theoretical or logistical problem. In fact, scale offers several opportunities for cost savings. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 2C: Maximize Equipment and Material Availability Alum is produced currently for the water supply industry. It is readily available from a number of sources. There are several contractors that have successfully applied alum to lakes; hence, this is not a limitation to the Lake Okeechobee program. In addition, because equipment and material handling do not require specific training and are made of common elements, a 30-day mobilization is all that would be required to start an alum treatment once permitting and funding issues have been resolved. The alum to supply the Lake Okeechobee treatment would require the excess supply from eight production 4/10/2003 engineers & scientists 4-18

106 facilities. Three facilities in Florida and five in Georgia have been identified as having that excess capacity available. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 2D: Maximize Permanence Alum treatment has proven to be the most successful in-lake management technology to date (Cook and Welch, 1999). Alum treatment s long-term success is a function of the control of external nutrient loading to the lake. For Lake Okeechobee, it is assumed that external nutrient loading would be controlled for the long term. This means that the effective period of P control in the lake is extended well beyond the normal 15 years used in the model projections. The alum would permanently control the P in the sediments of the lake but would not control the P deposited onto the lake sediments after the treatment is completed. If this P is in excess of the newly deposited sediment s capacity to retain P, it would become available to the water column. So, while the P already in the sediment would be effectively held there by the aluminum added to the sediments during the alum treatment, newly deposited P will potentially become available. If the alum floc or more properly, the aluminum hydroxide (Al[OH] 3 )polymer, were physically disturbed (e.g., by wind action), it would resettle to the bottom of the lake and would remain effective in retarding the migration of mobile P from the sediment to the overlying water. This is because it is the ratio of aluminum to phosphorus in the sediments that would control internal cycling of P. This ratio would not change as a result of physical mixing. Also, it has been repeatedly observed that alum floc that has been disturbed by mixing from wind or boats redistributes to cover the deep sediments that are the target of an alum treatment. Alum floc that is displaced to the littoral areas could migrate back to the pelagic zone, re-covering those sediments again within days to weeks of a major wind event (Gibbons and Welch, personal communication). However, District scientists have found that resuspended particles are transported to either shallow bays at the south and west sides of the lake or out of the lake at major outflow structures. If this is the case, portions of the pelagic zone could be left with less than optimal alum coverage. The downside of alum treatment to control P is that repeat applications could be required about every 15 years, unless external load reductions occur as planned. 4/10/2003 engineers & scientists 4-19

107 Despite these potential issues, chemical treatment is still likely to perform well from a permanence perspective; therefore, this performance measure has been given a score of PM 2E: Minimize On-Shore Land Use Needs and Conflicts The only land-use requirements are the need to offload the alum and sodium aluminate into holding tanks or barges. This would require approximately ½ to 1 acre of land with shoreline access for a tanker truck to maneuver. This land would be lost to any other use for the 2-year treatment period. There would be significant truck traffic (see Section ) associated with this alternative that could cause a conflict with existing traffic patterns and levels. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of Satisfy Permitting Requirements An ERP and an Environmental Impact Statement (EIS) would be required in advance of implementing a full-scale alum treatment program in the lake. Additionally before the FWC, FDEP, USACE (and possibly others) would consider signing off on an alum remedy (which would be required before an EIS could be approved and/or an ERP could be issued), a comprehensive in-lake pilot test would be required. There are a number of negative perception issues associated with this alternative. There is grave concern that alum is highly toxic to fish, and there is a perception that adding a chemical to a natural system is inherently a bad idea. Because of these perceptions, the permitting agencies would need to be educated about the following: Alum is not toxic to the aquatic ecosystem or to humans. It is true that aluminum can be toxic if organisms are exposed to the trivalent form of the aluminum ion. However, this aluminum ion is not found in the ph ranges (6.0 to 8.5) encountered in the lake. In fact, the trivalent aluminum ion is only abundant at ph ranges below 4.5. This means that the toxicity of aluminum is alkalinity dependent; therefore, if the alkalinity of the system is not exhausted and the ph is maintained at 6.0 or above, aluminum toxicity will not occur (Gensemer and Playle, 1999). 4/10/2003 engineers & scientists 4-20

108 Alum is routinely used in the treatment of water supplies, so its use in the lake should have no impact on water supply except to improve it. Aluminum concentration in the lake would not increase due to the alum treatment. Sulfate concentrations would increase during the treatment period, but would not increase to the point of exceeding water quality standards. The sulfate concentration would return to background levels at a rate similar to the hydraulic flushing rate. Both zooplankton and benthic invertebrate populations have increased in diversity and abundance after other alum treatments (Cooke et al, 2002), and the same is expected in Lake Okeechobee. Although there is good evidence that this alternative could be implemented without causing harm, demonstration of this is expected to be difficult and controversial; therefore, this performance measure is given a score of Goal 3: Maximize Cost Effectiveness The total estimated cost of alum treatment is $493 million. This total is based on the following assumptions: 1) Treating the sediments in the entire 80,000-ha pelagic zone (34% of the lake s total 233,000 ha); 2) Capital costs of $3,125/ha, or a total of $250 million (estimated by adjusting the average cost per ha in 1990 dollars presented in Cooke et al. [1993] for inflation, as well as by cost of material applied); 3) Contingency costs of $108 million; 4) Environmental documentation costs of $2 million; 5) Pilot study to confirm dose and clarify scale-up issues at a cost of $0.5 million; and 6) Final design and construction management costs of $45 million. The cost estimate summary for this alternative is presented in Table 4-1, with details presented in Appendix E. NPV, which is used to evaluate construction and operating expenditures that occur over 4/10/2003 engineers & scientists 4-21

109 different periods of time by discounting all future costs to a common base year, is also presented on Table 4-1. NPV allows comparisons on the basis of a single figure, which represents the amount of money that, if invested in the base year, would be sufficient to cover all costs over the planned life of the project. Using a beginning-of-year discount rate (adjusted for inflation) of 5.8 percent, the 2002 Net Present Values for the chemical treatment alternative is $275 million. Table 4-1 Conceptual Cost Estimate - Alternative 2 - Chemical Treatment Summary Estimate Item Estimated Description $/y 2 Net Present No. Amount Value $/y 2 1 Chemical Treatment $336,514,000 $0.37 $186,200,000 $ Operations Monitoring and Construction Management $22,300,000 $0.02 $12,400,000 $0.02 DIRECT CAPITAL COSTS SUBTOTAL $358,814,000 $0.39 $198,600,000 $ Design and Indirect Capital Costs $132,700,000 $0.15 $75,100,000 $0.08 TOTAL CAPITAL COSTS $491,514,000 $0.54 $273,700,000 $ Annual Long-Term Operation, Maintenance and Monitoring (OM&M) $120,000 PRESENT WORTH OF OM&M (50 Yrs. at 5.8%) $1,000,000 $0.00 $1,000,000 $0.00 TOTAL COST OF SCENARIO $492,514,000 $274,700,000 TOTAL COST PER SQUARE YARD OF AREA TREATED $0.54 $0.30 Notes: 1. Chemical treatment using alum and sodium aluminate would be applied to the pelagic zone of Lake Okeechobee. This would cover 80,000 ha or 34% of the lake's total area of 233,000 ha. Treatment would be performed by a single pass on each selected area. Eight crews would work simultaneously over a period of 21 months. 2. Operational Monitoring and Construction Management includes $20,191,000 for construction management and $2,147,000 for engineering oversight, confirmation sampling and analyses. 3. Design and Indirect Capital Costs include 30% contingencies ($107,644,000), engineering, permitting and access ($24,529,000). 4. Annual Long-Term Operation, Maintenance and Monitoring (OM&M) includes sampling and analyses of sediments and water columns at 20 stations annually for 50 years. The estimated costs to implement alum treatment rely on certain component costs; estimates of these costs required the application of some conservative assumptions to deal with issues of uncertainty. These include the following: The largest single component cost is the price and quantity of sodium aluminate for buffering the ph suppression resulting from alum addition. As discussed below, bench or pilot testing 4/10/2003 engineers & scientists 4-22

110 can help quantify these requirements. Buffering materials other than sodium aluminate should also be evaluated. A 50% reduction in this component cost could reduce the project total by around $100 million. Alum price and quantity is the second largest component cost. As discussed in Section 4.1.1, several methods for estimating alum dosage requirements were compared. Without pilot testing results, it is not prudent to suggest potential dosage reductions at this point. The estimated unit purchase prices for alum and sodium aluminate are very competitive, reflective of the huge quantities required by the project. Further price reductions on the order of 5% to 10% would reduce total project cost by around $18 to $36 million. Transportation costs for liquid alum and sodium aluminate assumed a somewhat conservative 820 miles using rail freight rates. Reliance on production facilities in Florida and Georgia and using barge deliveries could potentially lower project cost on the order of $45 million. One supplier has suggested building a new production facility in southern Florida to serve this project and other markets. This could potentially cut another $45 million from the estimated project cost. Each of the eight chemical application teams assumes a barge, pumps, two boats, five crew members, and a fuel boat. Reducing labor by 20% would save around $2 million PM 3A: Minimize Construction Costs Because of the scale of any activity on Lake Okeechobee, the cost of alum treatment is substantial, at $493 million. However, this is an order of magnitude less than the estimated cost of Alternative 3 (dredging), and the treatment is likely to be more effective. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 3B: Minimize Operation and Maintenance Costs Given the model results, which predict that the in-lake target concentrations of P in Lake Okeechobee would be achieved after the alum treatment in 2015 (Figure 4-3), it would appear that only one alum 4/10/2003 engineers & scientists 4-23

111 treatment may be needed. However, if external load reductions are not achieved as planned, additional applications would be needed about every 15 years. After completion of chemical treatment, there would be some long-term maintenance and monitoring activities. The estimated costs also include quantification of NPV using procedures and discount rates recommended by the USEPA (2000). This approach assists in evaluating the tradeoffs between alternatives with different balances of construction versus O&M costs. The 2002 costs (NPV) to implement alum treatment are $275 million, assuming chemical applications in 2012 and This performance measure for the Chemical Treatment Alternative has been given a score of 2. This is primarily associated with the potential need to re-treat the sediment if the external loads are not reduced PM 3C: Maximize Benefits (Material Reuse) Alum treatment would result in no material re-use because all materials are applied to the lake. Treatment barges are already in use, so there would be no return due to their re-use. Therefore, this performance measure is not applicable to the Chemical Treatment Alternative Goal 4: Maximize Environmental Benefits The perceived disadvantage of toxicity resulting from alum treatment has seldom been a problem and can realistically be prevented with proper pre-testing and buffering, as necessary. Potential toxicity in Lake Okeechobee is less of a concern than in other lakes due to its high alkalinity. While the size of the lake would require a period of protracted treatment (2 years), only a small fraction of the lake s fish would be in contact with the application at any one time. Further, there is no evidence of toxicity to fish directly from aluminum. Fish that are present during the alum application at the time of floc formation can have the floc coat their gills and, in some cases, this coating could inhibit the absorption of oxygen, resulting in appoxia (Cooke et al., 1993). Adverse effects on the lake s benthic organisms 4/10/2003 engineers & scientists 4-24

112 are expected to be minimal and only short-term (Cooke et al., 1993), and, most often, the invertebrate community increases in diversity and abundance after an alum treatment in response to the improved water quality (Cooke et al., 2002) PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone The decrease in in-lake P concentration would result in a decrease in both phytoplankton concentration and occurrence of algal blooms within the littoral region. This would, in turn, result in greater water clarity and an increase in the growth of rooted aquatic plants within the littoral zone. In addition to improved rooted plant growth, the overall diversity of the littoral plant and animal communities would increase due to the positive changes that improved water quality conditions would create. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 4B: Maximize Benefits to Submerged Aquatic Vegetation An alum treatment of the pelagic zone would result in increased water clarity throughout the lake, and this would result in an increase in the SAV growth, coverage, and diversity. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities Lake Okeechobee is an extremely productive system, and an alum treatment would reduce the overall production of the algae within the lake. However, by meeting the goal for phosphorus concentration, the lake would still be very productive. In addition, a significant portion of the current algal productivity is generated by blue-green bacteria. Their production does not efficiently integrate into the food chain, and it is this excessive production by blue-green bacteria that would be greatly impacted by the reduction in P concentration in the lake. Lower quantities of blue-greens would result in an increase in overall algal diversity and production that would be fuel for the food chain. This, in combination with the overall reduction in suspended materials, would result in an improvement of habitat and potentially would lead to an expansion of the existing fisheries within the lake. 4/10/2003 engineers & scientists 4-25

113 The invertebrate community within the littoral areas of the lake and the northern portion of the lake, which accounts for most of the diversity and a significant amount of the invertebrate production in Lake Okeechobee, would be outside the alum treatment area. The greater productivity of these areas is presently due to the relative area of littoral versus pelagic areas, but, more importantly, due to much greater habitat diversity that exists in the littoral areas due to rooted plant communities and substrate differences. In contrast, the pelagic substrate is mainly mud across the entire area, and the physical and biological structure that rooted aquatic plants provide is virtually nonexistent. The indirect effect of expanding the submerged plant community coverage and diversity after an alum treatment should only enhance the invertebrate population in the lake. The invertebrates within the pelagic area would be exposed to the alum treatment, and a portion of the zooplankton population could become entrapped in the alum floc during the floc formation and as it settles to the bottom. The majority of these zooplankton would escape the floc within 24 hours and return to the water column to continue to graze on phytoplankton. No long-term impacts on zooplankton population have been observed after alum treatments (Gibbons et al., 1984). Benthic invertebrates have been observed using the alum floc on the sediment after an alum treatment, and no toxicity has been documented in buffered alum treatments (Cooke et al., 2002). The mode of potential toxicity to benthic invertebrates is by exposure to trivalent aluminum ion; however, significant concentrations of this form of aluminum do not exist at ph ranges found in Lake Okeechobee. Hence, there should be no direct toxicity to the benthic invertebrate community. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of 3 in both the short and long term PM 4D: Minimize Negative Impacts to the Manatee The alum treatment would have no long-term adverse impact on manatee population. The result of the treatment would, in fact, be an improvement in water clarity and result in expansion of the rooted aquatic plant beds that should improve overall habitat for the manatee. However, during the 2 years that alum is being applied, impacts could occur in cases where the manatee would be slow to move out 4/10/2003 engineers & scientists 4-26

114 of an area where alum is being applied. Although engineering barriers would be set up to prevent access of manatees to the application areas, a very strict manatee watch program would need to be implemented, and the alum application process would need to be slowed or discontinued in the presence of manatees. This performance measure for the Chemical Treatment Alternative has been given a score of PM 4E: Minimize Negative Impacts to the Alligator The alum treatment should have no adverse impact on the alligators habitat or food supply in the Lake Okeechobee marsh areas. The primary impact of alum would be in the pelagic zone, and would not impact marsh plants or other biota. For the alligators that find themselves in the pelagic zone during chemical treatment application, there is some potential for impact. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 4F: Minimize Negative Impacts to the Okeechobee Gourd The Okeechobee Gourd would not be adversely impacted, nor would it necessarily benefit from the pelagic zone alum treatment. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds The alum treatment would be conducted in the pelagic area of the lake and would have no adverse impact on the snail kite or wading birds that forage in the littoral zones of the lake. Therefore, this performance measure for the Chemical Treatment Alternative has been given a score of 3. 4/10/2003 engineers & scientists 4-27

115 4.4.5 Goal 5: Maximize Socioeconomic Benefits PM 5A: Maximize Regional Socioeconomic Benefits The two possible negative socioeconomic impacts of Chemical Treatment result from the presence of eight spray barges on the lake for 21 months and the truck traffic necessary to supply the barges. The area to be treated is approximately one-third of the lake surface, primarily in the center of the lake. The spray barges are large and slow moving and will only be operated during the day. Since most of the fishing activity in the lake takes place near shore and in shallow water (i.e., not where the barges will normally be present except when they are being serviced), large slow barges are easy to avoid, and the project will only take 21 months, there is likely little economic impact from the barges. If each barge has to return to a staging area to take on a new load of alum there will be significant barge traffic to and from the site every morning and afternoon. This could pose an impact on the fishing near the staging area and also create a heightened danger of collision between barges and other traffic on the lake. Socioeconomic Problems The transport of alum to the staging areas presents a nuisance problem. Each barge will distribute approximately 100,000 gallons (22,200 kg) of alum per day. If a single site is used and the trucks are scheduled to arrive over an 8 hour period, a truck will arrive, unload, and depart approximately every 40 minutes over the eight hour work day. 22,200 kg x 2.2 pounds(lbs)/kg = 48,840 lbs of alum per barge assume that each truck can carry a 30,000 lb payload (a standard 2 axel dump truck) 48,840 lbs/barge ) 30,000 lb truck. 1.6 trucks/day/barge 1.6 trucks/day/barge x 8 barges. 13 trucks/day 13 trucks/day ) 8 hour period. 1.6 trucks/hour or one truck every 40 minutes This seems to be a manageable problem, but people living near the staging site will notice an increase in the noise, dust, etc., that accompany each arrival, unloading, and departure cycle during the period 4/10/2003 engineers & scientists 4-28

116 that alum is being applied to the lake. The problem would be increased to the extent that the unloading process is noisy, messy, and/or takes a long time. Further, this discussion assumes that the spray barges will be loaded sequentially during the course of the day. If they are all loaded at the same time every morning or every evening, the nuisance will be for a shorter duration, but potentially louder and messier. Each staging site is estimated to take half an acre and require construction of an access road. The negative aspects of a staging site are the removal of native vegetation and potential spills of alum and petroleum products from the trucks and the barges. These are manageable issues, and the cost to restore one or more staging areas to their original conditions after approximately two years of use is included in the project budget for this alternative. Socioeconomic Benefits The primary benefit is an increase in construction/hauling-related jobs, and the potential benefit from construction of an alum processing facility. With regard to the construction/hauling jobs, a crew of approximately 100 people will be necessary to operate the 8 spray barges for 8-hour work days. In addition, assuming that a single truck could make two trips per day to bring alum to a staging area, the 13 trips per day necessary to supply the spray barges suggests approximately 8 trucks and drivers, allowing for normal time off, down time, etc. If these drivers lived on the Lake Rim it would result in approximately 8 additional jobs hauling alum to the barges. An approximate economic benefit for these jobs can be calculated using SIC 17-construction-special trade and SIC 42-motor freight transportation and warehousing. Using 2001 data from Appendix D Table 3B, the Lake Rim s average sales per employee in SIC 17 was $148,448 and for SIC 42, $98,655. Multiplying these figures by the estimated number of new jobs yields an estimated increase in economic activity in the region of $15,638,040 per year for two years. SIC 17 construction-special trade 100 $148,488 $14,848,800 SIC 42 motor freight transportation and warehousing 8 $98,655 $789,240 4/10/2003 engineers & scientists 4-29

117 This activity represents an increase of 0.4% in the region s total economic activity for 2001 ($3,784,000,000). The monitoring activity, estimated to continue for 20 years would yield negligible economic benefit. The second benefit would accrue if an alum processing facility were to be constructed in the Lake Okeechobee region. At this time there is insufficient information to calculate an estimated benefit from this activity. On an annual basis it would probably not approach the one-time economic impact of the chemical treatment; however, it would provide a long term income source. It would also be a basic activity to offset, to a small extent, the variability associated with the region s primary activity, agriculture. In summary, the negative aspects of chemical treatment would be the creation of a nuisance caused by truck traffic bringing alum to the staging area, unloading it, and departing; and barge traffic to and from the staging area(s). Positive aspects of this alternative include a two-year increase of approximately 110 local jobs, a one time economic boost of approximately $13 million per year for each of two years, and the potential of the creation a long term, basic, industry. As a result, this performance measure has been given a score of PM 5B: Minimize Environmental/Social Inequities Social inequities are measured by how evenly the positive and negative impacts are distributed. As a practical matter this is best evaluated by the economic and social characteristics of the locations where the alternatives are implemented. As described in Appendix D, the Lake Rim s characteristics make evaluating environmental and social inequities a straightforward task. The economic conditions are strongest on the western half or the Lake Rim and they weaken toward the eastern rim. Similarly, the economies of the western cities are more evenly distributed across economic sectors than are those of the eastern cities. 4/10/2003 engineers & scientists 4-30

118 Ethnically speaking, a large majority of the small number of American Indians in the region live on the northwest rim. Similarly, a large proportion of the sizable African-American population living on the lake rim lives on the southeastern rim. The equally large population of people of Hispanic cultural heritage is relatively evenly spread throughout the region with a slightly higher concentration in the east than in the west. In this alternative both the positive and negative impacts revolve around the number and location(s) of the spray barge staging areas. The site or sites will bring jobs and minimal environment impact, but they will also bring an increase in truck traffic. On balance, however, a staging area is a benefit to a locality. Therefore, although the exact location(s) remains to be set, locating sites in the eastern areas would have proportionately greater benefit to the eastern area than a similar site in a western area. The best situation from a purely environmental and social justice point-of-view would be to build three staging areas, two in the eastern areas and one in the western area. It is not known, however, if this approach is practical. Therefore, this performance measure has been given a score of PM 5C: Maximize Community Acceptance As mentioned earlier in this section, chemical treatment is widely perceived as a bad choice for the lake by both the public and regulators. There is grave concern that alum is highly toxic to fish, and there is a perception that adding a new chemical to a natural system is inherently a bad idea. The specific areas of community and interagency concern that have been raised include: Long-term ramifications of the application of a potentially toxic chemical to such a large, fragile ecosystem; Long- and short-term effects on benthic invertebrates of the system; Potential for increasing incidence of mercury methylation in the water column as a result of using alum; and The potential for periodic reapplication of alum in the future. 4/10/2003 engineers & scientists 4-31

119 Because of these perceptions, the community at large would need to be educated about the following: Alum is not toxic to the aquatic ecosystem or to humans. It is true that aluminum can be toxic if organisms are exposed to the trivalent form of the aluminum ion. However, this aluminum ion is not found in the ph ranges (6.0 to 8.5) encountered in the lake. In fact, the trivalent aluminum ion is only abundant at ph ranges below 4.5. This means that the toxicity of aluminum is alkalinity-dependent; therefore, if the alkalinity of the system is not exhausted and the ph is maintained at 6.0 or above, aluminum toxicity will not occur (Gensemer and Playle, 1999). Alum is routinely used in the treatment of water supplies, so its use in the lake should have no impact on water supply except to improve it. Aluminum concentration in the lake would not increase due to the alum treatment. Sulfate concentrations would increase during the treatment period, but would not increase to the point of exceeding water quality standards. The sulfate concentration has been observed to return to background levels at a rate similar to the hydraulic flushing rate. Both zooplankton and benthic invertebrate populations have increased in diversity and abundance after other alum treatments (Cooke et al., 2002), and the same is expected in Lake Okeechobee. Legal challenge is always an issue with environmental projects. The likelihood of legal challenge prior to the receipt of a permit is always present. As in the case study for Green Lake in Seattle in 1992 (based on Public Awareness Program conducted in support of the 1991 Green Lake alum treatment; Gibbons, personal communication), grassroots campaigns are likely to sprout up to challenge the application of alum to the lake during the decision-making process and up until a permit is granted. Although there is good evidence that this alternative could be implemented without causing harm, demonstration of this is expected to be difficult and controversial; therefore, this performance measure is given a score of 2. 4/10/2003 engineers & scientists 4-32

120 PM 5D: No Impacts on Water Supply or Lake Operations Alum is routinely used in the treatment of water supplies, so its use in the lake should have no impact on water supply except to improve it. Aluminum concentration in the lake would not increase due to the alum treatment. Sulfate concentrations would increase during the treatment period but should not increase to the point of exceeding water quality standards. The sulfate concentration would return to background levels at a rate similar to the hydraulic flushing rate. Any activity to implement alum treatment in the lake could comply with Lake Okeechobee regulations schedules and operations. The application area of the pelagic zone is some distance from the locks and water utility infrastructure located on the lake. No conflicts are expected. This performance measure is given a score of 4. 4/10/2003 engineers & scientists 4-33

121 5. Alternative 3 Dredging with Confined Disposal Facility 5.1 Final Alternative Development This section focuses on dredging with three post-dredge confined disposal facility (CDF) sediment management options. The three CDF management options discussed are 1) in-lake islands, 2) shoreline disposal, and 3) upland disposal. A CDF is a confined area that can either be located on land or in water, where sediment can be contained and managed once it is removed from a lake, harbor, river, or other aqueous setting. A variety of post-dredge sediment management options were initially considered in the Development of Alternatives and Work Plan phases of this FS project; however, following a subsequent detailed beneficial use analysis, use of a CDF was deemed to be the most feasible option and included the three potential locations identified above. The beneficial use study, led by OA Systems Corporation (OA Systems Corporation, 2002), was a focused effort to evaluate a full spectrum of possible beneficial uses such as brick manufacture, soil blending for landfill cover, highway roadfill, topsoil for agriculture, fertilizer, beach renourishment, habitat enhancements, islands, and near-shore marshes. Following the evaluation of land use, vegetation types, soil types, sediment volumes, sediment chemistry, feasibility, cost, economic benefits, and regulatory considerations (and after conducting a brainstorming meeting with Institute of Food and Agricultural Services [IFAS], Florida Department of Agricultural and Consumer Services [FDACS], FDEP, the District, and other interested parties), OA Systems found that the option with the most potential for addressing Lake Okeechobee s needs would be construction of large CDFs, either as islands or on-shore. Land improvements/land application/top soil mixes were found to rank second in OA s feasibility analysis. However, despite the fact that arsenic levels in sediment do not exceed USEPA s sediment criteria for freshwater (USEPA 2000), both residential and commercial soil CTLs, as defined by FDEP , may be an issue if the sediment were to be excavated from the lake and used for soil products (Tables 4 through 7, Appendix B, sediment quality data for 2002). Additionally, land application rate limits for nutrients (established 4/10/2003 engineers & scientists 5-1

122 by IFAS and FDACS and enforced by FDEP) in the watershed and across Florida would severely constrain potential sellers and buyers of soil products. Without willing buyers and willing sellers, the marketability of these products would be limited. The development process for the dredging alternative also contemplated the inclusion of combination or hybrid alternatives, such as chemical treatment followed by dredging. However, the results of the preliminary modeling indicated that there was little value in combining dredging and chemical treatment. This is based on the modeling results for chemical treatment (as a single-dose application), which demonstrate that chemical treatment will be effective long enough for reductions in external loads to control TP levels in the lake. As such, this obviates the potential need for adding a subsequent dredging step. This decision is supported by the results of the effectiveness modeling conducted for dredging, which indicates dredging is ineffective in reducing water column concentrations of TP. The development of alternatives also contemplated dredging from the central portion of the lake in a depression, or sump. The concept was based on the thought that the lake s concentric circulation would essentially collect a majority of the sediment in the sump, and allow a focused dredging effort in that area. The sump itself could be either a natural depression in the lake s bottom, or an area excavated to form the sump. As this concept was further investigated, several limitations were identified: the lack of natural relief on the lake s bottom would require the excavation of a sump; there may be potential impacts to the underlying aquifer if a sump were excavated in the limestone layer directly beneath the sediment; and a slow rate of dredging (a few million m 3 per year) would be necessary to keep pace with movement of sediment into the central portion of the lake, in contrast to the removal rates required to complete the dredging process within a reasonable timeframe (over 10 million m 3 per year). Based on the process and information described above, this feasibility study focuses on dredging with long-term sediment management using a CDF. This alternative is further described and evaluated in the remainder of this section. 4/10/2003 engineers & scientists 5-2

123 5.2 Detailed Description Dredging with Confined Disposal Facility (CDF) This remedial alternative includes the dredging of approximately 161 to 177 million m 3 of phosphoruscontaining sediment from Lake Okeechobee. Disposal and long-term isolation of this sediment would be accomplished by placing the dredged sediment within the protective confines of one or more multicelled CDFs. In addition to dredging, this remedial alternative includes transportation of the sediment from the point of dredging to the CDF(s) via hydraulic pipeline. The CDF(s) would also be used to treat the excess water generated during dredging prior to returning this water to the lake. Water treatment would be conducted in a two-step process, beginning with gravity settling to separate the solid-phase sediment particles from the excess water generated during the dredging process. Additional water treatment steps, including precipitation and enhanced sedimentation, would also be conducted within the CDF(s). These additional water-treatment measures might be necessary to treat the water generated during dredging in order to achieve the phosphorus restoration target of 40 µg/l prior to release back into the lake. Three sub-alternatives were evaluated. Alternative 3A includes two island CDFs constructed in the center of the mud zone (see Figure 5-1). Alternative 3B includes construction of one shoreline CDF along the eastern portion of the lake (see Figure 5-2). Alternative 3C includes construction of one upland CDF within a distance of 6 km from Lake Okeechobee (see Figure 5-3). Note that the proposed locations of the CDFs are undefined, and it would be necessary to evaluate underlying foundation conditions. After completion, the top(s) of the CDF(s) would be stabilized with vegetation. In addition to preventing runoff and phosphorus migration into the lake, the plantings would also be designed to provide a beneficial use through the creation of terrestrial and wetland habitats. The island or shoreline CDF(s) would also provide a beneficial use through the creation of additional littoral zones within the lake. These additional littoral zones would include the fringe areas around the island or shoreline CDF(s), as well as new littoral zones that would be expected to form along the eastern shoreline of the lake due to changes in the lake s circulation caused by the presence of the CDF(s). Regular monitoring and maintenance, as well as periodic repairs to the CDF(s), would be necessary to maintain their functional integrity over the long term. 4/10/2003 engineers & scientists 5-3

124 The general assumptions used to develop the Dredging with CDF Alternative are further described below General Assumptions for Dredging with CDF Alternatives Target Area For the purposes of this FS, it was assumed that all sediments within the pelagic mud zone greater than 10 cm deep would be dredged. Laboratory studies conducted by Dr. Ramesh Reddy (Reddy et al., 2002) to simulate the effects of dredging Lake Okeechobee sediments (using sediment cores) showed that, based on his work, there was no compelling reason to target only a portion or a specific thickness of the lake s pelagic zone sediment (Reddy, personal communication). Despite this finding, the 10 cm minimum thickness was assumed because dredging precision for thicknesses less than 10 cm has not been demonstrated for the types of large dredges that would be needed for a project as large as Lake Okeechobee. It is technically infeasible to remove a very thin layer of sediment (ranging in thickness from 0 cm to less than 10 cm) with such crude construction equipment. The only sediments more than 10 cm deep that would not be dredged are those sediments located in the footprint of the areas where the island or shoreline CDF(s) would be constructed. Since the island or shoreline CDF(s) would be used to isolate the phosphorus-containing sediment from the waters of the lake, there would be no need to initially remove these sediments from the CDF locations and then replace them within the CDF(s). This approach saves the removal of around 17 million m 3 (Alternative 3A) or 3 million m 3 (Alternative 3B) of sediment within the CDF footprints. This results in a total in-situ dredge volume of approximately 161 million m 3 (Alternative 3A) or 175 million m 3 (Alternative 3B) of phosphorus-containing sediment. Alternative 3C is not constructed above phosphorus-containing sediment and therefore would involve removal of all 177 million m 3 of sediment within the mud zone greater than 10 cm deep. 4/10/2003 engineers & scientists 5-4

125 Sediment Characterization Additional chemical and geotechnical characterization of sediment from the mud zone was performed for sediment core samples acquired by BBL during September and October These results are included in Appendix B. Table 12A in Appendix B lists dry bulk density results (g/ml) for sediment cores acquired from 26 stations and sectioned into two intervals (0 to 15 cm; and 15 cm to Base). Evaluation of these data showed that the overall average of all 52 samples was 0.18 g/ml (range 0.08 to 0.35 g/ml). The average of the 26 samples from the 0 to 15 cm interval was 0.14 g/ml (range 0.08 to 0.19 g/ml). The average of the 26 samples from the 15 cm to Base interval was 0.23 g/ml (range 0.14 to 0.35 g/ml). These results are similar to data presented in the Sediment Erodability report (Hwang and Mehta, 1989), which included density and shear strength for 135 sections from 15 cores. Assuming a solidsspecific gravity of 2.14, the overall average of calculated dry density for all 135 samples was 0.22 g/ml (range 0.01 to 1.5 g/ml). The average of the 65 core intervals 0-10 cm was 0.11 g/ml (range 0.01 to 1.5 g/ml). The average of the 70 core intervals below 10 cm was 0.33 g/ml (range 0.14 to 1.5 g/ml). The five sediment samples analysed during the pilot dredging program (EA Engineering, Science, and Technology, Inc. [EA], 2002b) had average dry density of 0.25 g/ml (range 0.22 to 0.28 g/ml). Geotechnical data are also included in Table 12 Appendix B. Eleven sediment samples had the following average properties: 33.9% organics; 23.2% solids w/w; 2.17 g/ml solids specific gravity; and 0.27 g/ml dry density. Sieve analyses averaged 69.7% passing a #200 sieve, with average sand content of 30.3%. Sediment heavy metals analyses are shown on Table 11 in Appendix B, with comparisons to FDEP CTLs for five exposure routes. These comparisons showed exceedances of CTLs for arsenic, and two isolated exceedances for iron. 4/10/2003 engineers & scientists 5-5

126 Dredging Approach Hydraulic dredging would occur at a rate of 150 m 3 to 200 m 3 of in-situ sediment per hour (m 3 /hr), per dredge. The dredging would likely be accomplished using hydraulic dredges ranging in size from 20 to 30 cm (8 to 12 inches [in]) Dredges of several different sizes would likely be necessary to accommodate the range of conditions present in the lake. These conditions include water depths that generally range from 2 to 4 m (6 to 14 ft) and sediment layers ranging from approximately 15 cm (6 in) thick along the outer fringe of the mud zone, to over 60 cm (2 ft) thick in the center of the mud zone. For the purposes of developing cost and schedule estimates, we have assumed that dredging would be conducted with ten 25-cm (10-in) hydraulic dredges, although as stated above, a range of dredge sizes would likely be incorporated into this type of project. The identification of a specific dredge-head that would be used with the hydraulic dredges has not been considered within this evaluation. Identification of a specific dredge-head would be made during the design of the project, or possibly during the contractor selection process, based on performance-type specifications. For this evaluation, several dredge-head types were considered potentially acceptable. This list includes, but is not limited to, a matchbox, dustpan, plain suction, and cutterhead, as well as an innovative dredge-head, such as the Sedcut dredge recently tested during the Lake Okeechobee Pilot Dredging Study (EA, 2002b) Dredged Material Transportation Dredged material would be pumped as a slurry directly to the CDF(s) using a series of booster pumps. The maximum range of pumping using a typical series of booster pump stations is on the order of 15 to 45 km. Typically, one booster pump is needed for every 1 to 3 km of pipeline. To implement this alternative, it would be necessary to pump the dredged sediment up to a maximum distance of 40 km (and potentially an additional 4 to 6 km overland to the upland CDF for Alternative 3C). Most of the dredging would take place within the thickest portions of the mud zone; as such, 2 to 25 booster pump stations per pipeline would typically be needed, depending on the specific location of each dredge. These pipelines can be either floated on the water surface or submerged. For this application, a combination of submerged and floating pipelines are considered to be the most likely approach, as submerged pipelines may be required in areas to facilitate certain lake uses, such as recreational 4/10/2003 engineers & scientists 5-6

127 boating and fishing. For overland transport (Alternative 3C), it is anticipated that individual hydraulic dredges would discharge to a lakeshore collection/pump station. Overland pumping would be provided by dual pipelines and booster pumps to the upland CDF location. Use of a dual system would reduce downtimes for dredging and processing if one pipeline becomes plugged or requires service. The collection sump would also be sized to allow some attenuation or collection of dredge slurry if one or both overland pipelines are temporarily down CDF Construction Before dredging could begin, it would be necessary to construct one cell of the CDF dikes. Once the first cell dikes are complete, dredging could begin, and the remaining CDF dikes could be constructed in parallel with the dredging operation. The CDF dikes would be constructed from imported fill material. The CDF configurations are assumed to be rectangular, with a bottom footprint of approximately 2.1 x 6.2 km (1.3 x 3.8 miles) for each of the two island CDFs (Alternative 3A). For Alternatives 3B and 3C, the bottom footprint would be approximately 3 x 9 km (1.9 x 5.6 mi). The walls would be 7.3 m (24 ft) high and generally rise 3 to 4 m (12 to 14 ft) above the water surface (Alternatives 3A and 3B). This height is required given the historical range in water levels in the lake and the need to prevent over-topping by waves during high-wind conditions. Constructing the CDF dikes would include transporting large quantities (approximately 6 to 8 million m 3 ) of fill material to the CDF location(s). This fill material would likely be brought in by barge, either from Gulf coast locations or from the east, possibly through the St. Lucie Canal. CDF dike walls exposed to the lake would be constructed with sand and large armor stones on the outer face to protect against erosion (Alternatives 3A and 3B). The interior of the CDF(s) would also include a series of inner dikes to facilitate the management and treatment of water generated during dredging. A second possibility for CDF exterior wall configuration is a typical rubble-mound dike. This wall is similar to those used as breakwaters and would include a layer of sand on the inner face to limit the migration of phosphorus over the long term. During the design phase of the project, an engineering analysis would be conducted to determine the most cost-effective approach for CDF construction. This evaluation would be best completed once the final configuration or footprint of the CDF(s) has 4/10/2003 engineers & scientists 5-7

128 been determined. Determining the final configuration of the CDF(s) could be completed during the design phase of the project, or as part of an EIS. In either case, the task would require a significant hydraulic modeling effort to assess the potential effects resulting from changes to the lake s circulation pattern (Alternatives 3A and 3B). Following the completion of dredging, the dredged material within the CDF(s) would be allowed to consolidate for a period of 2 to 10 years before placement of vegetation or other habitat enhancements. A regular monitoring, maintenance, and repair program would also be required to maintain the effectiveness of the CDF(s) over the long term. For Alternative 3C, it is assumed that groundwater monitoring wells would be placed at regular intervals (perhaps 1,000 ft) around the upland CDF perimeter Water Treatment The large quantity of decanted carriage water generated during the dredging and consolidation processes would be collected from the CDF(s) and treated prior to discharge back to the lake. The unit process operations used for treatment of the water include sedimentation, first without and then with phosphorus precipitation agents. The first phase of treatment would consist of solids settling in ponded areas of the CDF(s). The supernatant from the first phase of settling would be routed to a chemical treatment area where phosphorus precipitation agents (e.g., ferric chloride or aluminum salts, along with polyelectrolyte flocculants) would be added to a rapid-mix chamber and then provided several hours contact with quiescent mixing. The water would then be introduced to another ponded area within the CDF for secondary sedimentation. The supernatant from the second phase of the process would be discharged back to the lake. Monitoring and sample analyses would be conducted to determine that treatment objectives are met. It is anticipated that the average treatment and discharge rate would be on the order of 106,000 to 117,000 cubic meters per day (m 3 /day) (28 to 31 million gallons per day [mgd]). For planning purposes, the dredged material slurry has been estimated to be approximately 5% (w/w) solids as it is pumped into the CDF. This is a decrease in solids content as compared to the in-situ solids content of 21% (w/w). 4/10/2003 engineers & scientists 5-8

129 Dredging Timeframe For evaluation purposes, we have assumed that dredging would be conducted 24 hours per day, 7 days per week. The actual productive time in terms of sediment removal would be 18 hours per day, which reflects a 25% down-time factor. This would account for planned and unplanned maintenance activities. The planned sediment removal rate for each dredge is approximately 1.1 to 1.2 million m 3 per year. Using the assumption of 10 dredges, the estimated duration of the sediment removal activity is approximately 15 years. However, this duration is based on the assumption that available CDF capacity does not become a limiting factor Overall Timeframe The overall timeframe for this project is estimated to be approximately 30 years, including a 10-year period for design and permitting and a 20-year period for construction and operation. The 10-year estimate for design and permitting is based on the magnitude of this project and the nature of the technical and procedural tasks that are necessary before construction could begin. These activities would likely include an EIS, engineering design, permitting, and construction contractor procurement. This 10-year duration recognizes the public nature of this process and includes time for review and comment on documents by the public, various interest groups, and multiple agencies. The duration also recognizes the procurement process that would likely be required for each of the major steps along the way, yet does not include the additional delays that could be encountered. These delays could be due to a number of potential factors, including the availability of funding, potential lawsuits, or protests of contract awards. Each of these could add time to the upfront, preconstruction schedule. The 20-year construction schedule includes 3 years of preparatory work before dredging begins [e.g., construction of the CDF(s) and other water treatment facilities], 15 years of active dredging, and 2 years of actively managing the CDF(s), demobilization, and restoration. Depending on the rate of sediment consolidation within the CDF(s), habitat development may not begin for a period of 3 to 5 years after dredging is completed (31 to 34 years after the start of the project). 4/10/2003 engineers & scientists 5-9

130 Land-Use Needs Approximately 2,570 ha (6,350 acres) of the lake would be required to construct the island CDFs (Alternative 3A). Approximately 2,740 ha (6,760 acres) of the lake would be required to construct the shoreline CDF (Alternative 3B). Approximately 2,780 ha (6,860 acres) of land would be required to construct the upland CDF (Alternative 3C). A small area (approximately several acres) would be required along the shoreline to support construction operations. This area would include a series of docks for work boats and for servicing the dredge equipment, as well as a material lay-down area. Material and equipment to construct the CDF(s) would be transported to the lake from Gulf coast locations or from the east, possibly through the St. Lucie Canal. Transport routings would be highly dependent on construction contractor selection Resources It is assumed that dredging would be accomplished by 10 dredging crews working 24 hours per day, 7 days per week for 15 years, with 25% down time. It is estimated that an on-lake dredging workforce of 240 personnel would be required for three shifts for the 10 crews, with up to 100 personnel working during one shift. These resources are required for debris removal, dredging, pipeline and booster pump maintenance, fueling, and silt curtain maintenance. Additional staff are required for management of docking and material handling areas; construction of CDF dikes; operating CDF filling, drainage, and dessication; water treatment; and CDF cover, planting, and habitat development. These activities would require another 20 to 40 personnel for each of three shifts during various stages of the project, in addition to the on-lake dredging crews Fugitive Short-Term Phosphorus and Solids Release During Dredging Water-quality monitoring was conducted during the 2002 Pilot Dredging Project, including ambient water-column sampling upstream, downstream, and within the dredging zone. As a result of these tests, it is not anticipated that there would be any significant P or solids release during dredging. During the pilot program, it was noted that turbidity monitoring data indicated no significant impact on lake turbidity levels during dredging. Turbidity values recorded before, during, and after dredging 4/10/2003 engineers & scientists 5-10

131 was completed did not differ from each other significantly (EA, 2002b). Furthermore, comparisons of metals in the water column to FDEP s water-quality criteria for Class I water bodies indicated that except for one iron value all other metal concentrations were below the water-quality criteria for Class I water bodies (EA, 2002b). The fugitive release results of the pilot program are supported by results of elutriate tests performed for samples from Lake Okeechobee taken on September 28 and 29, 2002, discussed below. Sediment samples from three locations in the lake were tested using a Modified Elutriate Test (USACE EM , p and EEDP-04-02) to evaluate potential releases from dredging. Sediment and water from each location was combined using a volumetric ratio of 1 to 4. These mixtures were then aerated for 1 hour and settled for 24 hours, after which the supernatant was sampled for testing of TSS; turbidity; TP; dissolved-p; ortho-p; and total metals Al, As, Be, Cd, Cr, Cu, Fe, Pb, Hg, Ni, Se, Ag, and Zn. The background water was also tested for these parameters. The analytical results are included in Table 9 in Appendix B and discussed below. The three bulk sediment samples from each location were analyzed for percent solids and TP. The percent solids results of 16.5, 24.1 and 20.6% (w/w) were similar to results of other studies (21% during pilot dredging [EA, 2002b]; 18.4% average of 135 samples from the Fine Sediment Erodibility study [Hwang and Mehta, 1989]; and 23.2% average of 11 samples from BBL s September/October 2002 sampling). The sediment TP results of 870, 620 and 830 mg/kg were lower than results of August 2001 samples from the pilot dredging site (PDS-01 and PDS-02) of 4,990 and 3,870 mg/kg. TP, dissolved-p, and ortho-p in the three background water samples were all slightly above the District goal of parts per million (ppm). It is notable that the supernatant water from the modified elutriate (24-hr settling) samples were consistently lower than corresponding background water samples for each of the parameters TP, dissolved-p, and ortho-p. While contact with the sediment reduced both total- and dissolved-p, the TP elutriate concentrations were still above the District goal of ppm. 4/10/2003 engineers & scientists 5-11

132 TP and ortho-p in the elutriate were also similar to and slightly lower than the chemical precipitation influent during pilot dredging testing (May/June 2002) of to ppm TP and to ppm ortho-p. TSS and turbidity in the supernatant sample were two to four times higher in the elutriate samples than in the corresponding background waters. Similarly, aluminum and iron were elevated in the elutriate samples, while other metals were generally below detection levels in both background and elutriate. Copper concentrations were slightly lower in elutriate than in background. Although there is a lot of P in the sediments, it is evidently tightly bound and does not readily leach into the elutriate water. TSS and turbidity elevations in the elutriate were not surrogate indicators of similar elevations in total- or dissolved-p Effectiveness Modeling In conducting the simulations of the effects of dredging on nutrient dynamics in Lake Okeechobee with the ILPM and LOWQM models, several fundamental assumptions were made: 1) Dredging of sediments would be restricted to sediments in the mud zone with bed thickness > 10 cm. 2) The estimated total area of sediments in the mud zone = 760,828,600 square meters (m 2 ). 3) The area of sediment with greater than 10-cm thickness = 511,335,200 m 2. 4) The undredged area of mud-zone sediments = 249,493,400 m 2 (32.792% of total mud-zone area). Dredging was assumed to begin in 2016, following completion of the requisite permitting and construction of the CDFs, and was assumed to require 15 years to complete (Figure 5-4). In setting up the ILPM model to conduct the Dredging with CDF Alternative simulations, it was important to include several considerations in the analysis. First, although dredging in the mud zone is designed to extend across the entire thickness of the mud zone to the beginning of the hard, shell-sand underlying substrate, the removal of mud would not be wholly efficient some residual mud is 4/10/2003 engineers & scientists 5-12

133 expected to remain. This veneer of residual mud likely would be greater in thickness than 5 to 6 cm (the total depth of the sediment boxes considered in the ILPM and LOWQM models, respectively). The physical and chemical properties of this veneer are expected to reflect an integrated average of the original sediment properties present across its entire thickness. For example, if the original sediment lens varied linearly in sediment TP concentration from concentrations of 1,000 mg/kg to 500 mg/kg from the surface to the bottom, respectively, the sediment TP for residual veneer would likely average 500 mg/kg. The second consideration was how to represent the rate of removal of mud in the model. Both the ILPM and LOWQM represent the areal extent of Lake Okeechobee as a single box. The sediments in both models are thus represented as well-mixed (vertically and horizontally) boxes, and the average concentration of sedimentary P at each point in time reflects the balance between inputs from sedimentation, losses due to deep burial and releases to the water column, and the amount of sedimentary P available at the beginning of the time step. Because the sediment box is well-mixed, a first order removal function was built into the ILPM that removed sediment at a rate sufficient to yield a total reduction of sediment TP of 67.21% at the conclusion of 15 years of dredging: J dredge = k dredge M sed TP sed (1) where J dredge is the removal flux of sedimentary TP from Lake Okeechobee due to dredging (milligrams of phosphorus per yer [mg P/yr]), k dredge is the first order removal rate (1/yr), TP sed is the sedimentary TP concentration (mg P/kg sediment), and M sed is the total mass (kg) of sediment in the surficial mud zone sediments as defined in Equation (2): (100 %H2O) M sed = A mud z sed ρ sed 100 (2) where A mud is the area of the mud zone sediments (m 2 ), %H 2 O is the percent water content (w/w) of the surficial mud-zone sediments, ρ sed is the bulk density of the whole mud (kg/m 3 ), and z sed is the depth of the sediment box (m). The required value for k dredge to remove 67.21% of the sediment TP mass after 15 years of dredging is /yr. 4/10/2003 engineers & scientists 5-13

134 In reality, Equation (1) represents only the gross removal rate of sediment TP during dredging, and it is necessary to add in the sedimentary TP reflected by the dredging residual. Assuming that the residual concentration that is expected does not change appreciably over the life of the dredging operation, Equation (1) can be rewritten to yield both first-order removal and a constant residual formation flux: J netdredge = k dredge M sed TP sed k phys M sed TP res (3) where k phys is the physical removal rate of sediment (and equivalent to the production rate of residual sediment; 1/yr), and TP res is the concentration of sedimentary TP in the residual sediment (mg TP/kg sediment). k phys equals (i.e., 67.21% 15 years). Sediment physical and chemical properties for the residual sediment were calculated from data supplied by Reddy et al. (2002). Average properties were first computed across the entire depth of mud sampled at a given station by weighting the property, Θ, by the sampling interval depth: n θi zi i= 1 θ interval = n (4) z i= 1 i Replicate cores were then averaged for each mud-zone station to yield a single value for Θ interval for each station. The overall mean value for the entire mud zone was then computed by averaging Θ interval across all the mud zone stations. Individual samples were eliminated from consideration if the calculated particle densities of the sediment grains were less than 1.0 or greater than 5.0 g/cm 3 based on the water content and dry sediment bulk density reported by Reddy et al. (2002). This screening was performed to minimize the inflated influence of analytical error on the bulk and particle densities of individual samples that arose because of large relative errors induced by small sample volumes. Out of a total of 100 mud zone sediment samples (nine stations and three replicates per station for 27 unique station replicate combinations), the screening eliminated 32 samples. 4/10/2003 engineers & scientists 5-14

135 Table 5-1 presents a summary of mud-zone sediment properties for screened surficial sediments, averaged across the entire depth interval. Vertical averaging of samples was conducted by weighting each observation by the thickness of the contributing sediment layer. Parameter Bulk Density (g/cm 3 whole sediment) Table 5-1 Properties of Mud Zone Sediment a Vertically Averaged Surface Mud Only Average σ Average σ Mass H 2 O (g/cm 3 whole sediment) Mass Solid (g/cm 3 whole sediment) % H 2 O Particle Density (g/cm 3 ) Particle Density (calculated) Surface Critical Shear (n/m 2 ) b NaOH Pi (mg P/kg) HCL Pi (mg P/kg) Total Pi (mg P/kg) NaOH Po (mg P/kg) Residue P (mg P/kg) Total Po (mg P/kg) Sum TP (mg P/kg) a Original sediment data from Reddy et al. (2002). b From Equation 4.16, Hwang and Mehta (1989). Note that the estimated Sum TP concentration shown in Table 5-1 is 845 mg/kg, which is equivalent to reducing the sediment TP concentration by 28.1% relative to current conditions. However, since the reduction in the most readily available sediment fraction (the non-apatite inorganic P fraction or NAIP) is 34.2%, this percentage was used to estimate the residual TP concentration. This equated to a residual TP concentration of 753 mg/kg compared to the initial conditions in the model of 1,144 mg/kg. 4/10/2003 engineers & scientists 5-15

136 For the LOWQM dredging simulation, sediment concentrations of all sediment phosphorus fractions were decreased linearly over the dredging period discussed above. The sediment P concentration at the end of the dredging period would be reduced by 34.2% Uncertainty Impacts and Issues There are several important sources of uncertainty in the simulations. The ILPM simulations assumed a first order P removal rate of approximately 7.4%/yr. For a well-mixed system, this would yield a total removal of 67.21% of the phosphorus initially present in the surficial sediments after 15 years. In reality, dredging 67.21% of the sediment area over 15 years does not equate to removal of an equivalent amount of the surficial sediment P initially present; rather some smaller fraction is removed, particularly if the sediments are well-mixed and easily redistributed. The actual areal dredging rate is predicted to be 4.481% of the mud zone per year for 15 years. For a well-mixed system, this equates to total removal of 49% of the surficial mud. 9 As a result, predicted results shown on Figures 5-5 and 5-6 likely define an upper limit for the effectiveness of dredging. Figures 5-7 and 5-8 compare simulated sediment and lakewater TP, respectively, at concentrations for k dredge equal to and 7.434% per year. At the lower rate, no net benefit inures from dredging; indeed, by the year 2025, dredging actually adds to the surficial sediment burden by reintroducing historically deposited P at concentrations higher than are predicted to reside in the surficial sediments under the No In-Lake Action Alternative (Figure 5-9). Other uncertainties include the estimated reduction in external phosphorus loads to the lake. The actual phosphorus loadings over time would have a significant effect on the effectiveness of this alternative. As an example, the ILPM predictions for dredging using a constant surface water phosphorus concentration of 157 µg/l to represent the current conditions in the lake indicate, at best, water column concentrations would be reduced to approximately 80 µg/l. Ten to 20 years after 9 One could argue that, as sediment is dredged and the neighboring undredged sediment redistributes across the dredged areas, sediment with lower TP concentrations from below the redistributing sediment would be exposed. While this is certainly a mitigating factor, the surficial sediment concentrations shown in Table 5 represent values integrated over a 10 cm depth, while the ILPM and LOWQM models consider total exchange depths of 5 and 6 cm, respectively. Thus, it would be necessary to remove more than 50% of the sediment before any dilution owing to sediment redistribution would occur. 4/10/2003 engineers & scientists 5-16

137 dredging, P concentrations in the water column would increase to about 90 µg/l, the same as the nodredge scenario (Figures 5-10 and 5-11) Model Simulations for Dredged Material Management Options The LOHTM was used to simulate the following: 1) One upland CDF (Model Simulation Run 1); 2) One shoreline CDF (Model Simulation Run 2); and 3) Two island CDFs (Model Simulation Run 3). The above alternatives were simulated with the post-dredging value of critical shear stress, determined from vertically averaged data from Reddy et al. (2002). Vertical averaging was conducted by evaluating each observation by the thickness of the contributing sediment layer. The vertically averaged value of surface critical shear stress is N/m 2. The base value of critical shear stress in LOHTM is 0.4 N/m 2. However, the surface value of critical shear stress from Reddy et al. (2002) data is N/m 2. Therefore, the above alternatives were also run with a post-dredging value of surface critical shear stress given by: τ crit = τ orig x τ vert / τ surf or τ crit = 0.4 x 0.558/0.474 = N/m 2 Hereafter, simulations performed with a critical shear stress of N/m 2 are designated by the letter A (i.e., Model Simulation Run 1A) and simulations performed with a critical shear stress of N/m 2 are designated by the letter B. 4/10/2003 engineers & scientists 5-17

138 Input File Changes For Model Simulation Run 1, the only required input change was the value of the surface critical shear stress. This change was performed on Card 8 of the file efdcwin.inp. This change was also performed for the CDF option runs (Model Simulation Run 2 and Run 3). Additionally, for the CDF option runs, the CDF footprints were accounted for with edits to the model input files. The required model cells were blocked out in the files cell.inp and celllt.inp. In addition, data for these inactive cells were removed from the files dxdy.inp, lxly.inp, sedb.inp, and sedw.inp. Finally, for Model Simulation Runs 2 and 3, the number of active cells was changed in the file efdc.inp. The desired model output was time series of TSS concentration for near-shore and littoral zone cells. These cell indices were determined by overlaying a map of the model grid on a diagram of the Lake Okeechobee zones. Some of these cells were initialized; however, with a large roughness value of one meter. The cells initialized with the large roughness value did not have flow moving through the cells, and so were not included in the cells groups for which output was desired. In order to produce the required model output files, these cell indices were added to Card 18 of the file efdcwin.inp Post-Processing As discussed above, the output processed for this task was time series of TSS for cells located in the near-shore and littoral zones. The model produced one time series file for each specified cell. Each file contained the TSS concentration for each model time step and for each of the model s five vertical water layers. A post-processing program was written that read each individual file averaged over the five vertical layers, and output these average values for each whole day time-step only. The postprocessing was finished in Excel, where the average daily TSS concentration for each zone (near-shore and littoral) was determined. 4/10/2003 engineers & scientists 5-18

139 Results Average daily and maximum daily values of TSS concentration in mg/l are provided in Table 5-2 for the near-shore and littoral zones. Figure 5-12 shows time series graphs of daily TSS concentrations averaged over each of the zones for each of the simulations. Simulation Number Table 5-2 Average Daily and Maximum Daily TSS Concentrations Average daily TSS (mg/l) Near-shore zone Maximum daily TSS (mg/l) Average daily TSS (mg/l) Littoral zone Maximum daily TSS (mg/l) 1A B A B A B Results of Evaluation Dredging Goal 1: Maximize Water-Quality Improvements PM 1A: Minimize Time to Achieve Phosphorus Target The target is the amount of time predicted for TP in the pelagic zone of Lake Okeechobee to recover to an average annual average concentration of 40 µg/l. According to the LOWQM predictions, an annual average concentration of 40 µg/l would be reached by 2063, while the ILPM predicts that annual average TP concentrations would reach 40 µg/l by approximately The ILPM was run with two potential post-dredge sediment TP concentrations, the first scenario included a post-dredge TP concentration of 753 mg/kg, and the second scenario included a post-dredge TP concentration of mg/kg. Evaluating these two scenarios provided information regarding the sensitivity of the post-dredge TP concentration that was used in the dredging alternative (i.e., 753 mg/kg). 4/10/2003 engineers & scientists 5-19

140 The results of both scenarios are presented on Figure 5-5 and indicate that using the lower of the two post-dredging sediment TP concentrations, the 40 µg/l goal would be achieved near the end of the dredging period in However, caution should be exercised when drawing conclusions based on these findings. First, the difference in estimated water column TP concentrations for the two models during the time period of 2031 to 2050 ranges from approximately 5 µg/l to 10 µg/l and is within the long-term variability of the model predictions. For example, after 2060, the TP-time curves for the two dredging scenarios and the No-Action Alternative are essentially equal and fluctuate between 39 µg/l and 47 µg/l. As such, small changes in estimated performance must be viewed carefully and within the overall uncertainty of the models. Secondly, the lower residual sediment TP concentration (376.4 mg/kg) used to evaluate model sensitivity is likely not representative of conditions that would remain after dredging. It is more probable that the residual sediment TP concentration after dredging would be reflective of the average TP concentrations for the sediment that was removed through dredging (i.e., a residual concentration of 753 mg/kg). The rational for this hypothesis is that surface sediment remaining after dredging is not un-dredged sediment from the lake s bottom. Rather, the surface sediment that remains after dredging is sediment that was resuspeneded during the dredging process and has settled back on the lake s bottom after the dredging operation was complete. This concept is supported by one of the case studies reviewed in developing this FS (BBL, 2001b). Specifically, the results of post-dredging sampling conducted at Lake Geeples in Germany indicated that surficial sediment phosphorus concentrations were only reduced from 1,480 mg/kg to 810 mg/kg (Van der Does et al., 1992). It is also interesting to note that these pre- and post-dredging conditions are similar to the concentrations used to model the effects of dredging for Lake Okeechobee. In reviewing the literature for other applicable case studies, there are limited examples where the data are sufficient to further quantify this issue. However, the USEPA recently conducted a pilot study of dredging equipment at the New Bedford Harbor Superfund Site to evaluate the effectiveness of dredging PCB-containing sediment. This dredging study included a pre- and post-dredging monitoring program that provides insight as to the effectiveness of dredging. While the chemicals of concern at the New Bedford Harbor Site are PCBs, this constituent is tightly bound to sediment (similar to 4/10/2003 engineers & scientists 5-20

141 phosphorus) and thus can be used to make general comparisons for dredging phosphorus-containing sediments. The results of post-dredging samples collected during the New Bedford Harbor dredging study indicate that despite dredging into the underlying materials, a layer of loose unconsolidated sediment collected on the surface of the areas that were dredged (Foster Wheeler, 2001). In addition to being physically similar to the sediment that was dredged (as opposed to the underlying sediment strata), the new layer of surface sediment had chemical concentrations that were 18 times higher than the target concentration for this project (10 mg/kg of PCB). The post-dredge surface sediment PCB concentration was also reflective of the sediment-pcb concentrations for the material that was dredged. Although the chemical constituent of interest for the New Bedford Harbor site is different than for Lake Okeechobee (i.e., PCBs as opposed to TP), the results in terms of dredging effectiveness are directly applicable to Lake Okeechobee. In considering the effectiveness of dredging, the data collected during the Lake Okeechobee Pilot Dredging Study were also reviewed (EA, 2002b). While in this study the sediment was not specifically sampled for pre-and post-dredge phosphorus concentrations, sediment bathymetry in the dredging area was evaluated. The results of this evaluation indicated that it will be difficult to remove all of the phosphorus containing sediment through dredging including the conclusion that areas dredged may not be 100% cleaned of any soft sediment since some lateral transport of material will likely be taking place, especially over longer periods of dredging activity. While not part of the pilot dredge study per se, post-dredge sediment samples were collected as part of a separate sampling effort four months after the pilot study was completed (Table 13, Appendix B). This supplemental sampling program included the collection of samples from the surface sediment layer (0 to 15 cm), as well at depth from two areas dredged during the pilot test. These results of the surficial samples indicate that TP concentrations exposed to the water column are on average, 1,144 mg/kg. This does not appear surprising as the results of the bathymetry data indicate that the dredged area had been completely filled-in with sediment from other areas of the lake after the dredging was completed. Given these factors, it appears the post-dredge residual TP concentration used in the modeling (i.e., 753 mg/kg) is, at a minimum realistic, and possibly even conservative. 4/10/2003 engineers & scientists 5-21

142 Finally, the model results also indicate that post-dredge concentrations below 500 mg/kg are less important over the long term. Figure 5-13 indicates that for the No In-Lake Action Alternative or the dredging scenarios (both the 753 mg/kg and the mg/kg residual concentration cases), the TP sediment concentration in the lake would converge on approximately 500 mg/kg. This trend is highly evident by 2060, and by 2080 the projected sediment TP concentrations under any of the three scenarios are essentially identical. Based on the concerns related to residual sediment remaining after dredging, the continuing contribution of P from this veneer, and that the reductions in TP are primarily attributable to external load reductions, this performance measure is given a score of PM 1B: Maximize Reductions in Water-Column Phosphorus Concentrations The target goal is an average TP concentration of 40 µg/l. Both the LOWQM and ILPM models predict that dredging will result in a long-term average TP concentration of approximately 40 µg/l (Figures 5-5 and 5-6). While the ILPM model predicts a slightly higher average TP concentration, this difference is within the uncertainty in the model predictions. Graphs presenting the predicted TP concentrations in the near-shore and pelagic zones are included as Figures 5-14 and 5-15, respectively. As discussed above under uncertainty, the ability to achieve the 40 µg/l is also a function of the actual reduction in the external loads. In evaluating the ability of dredging to achieve a 40 µg/l goal, consideration was also given to the body of case study literature. Unfortunately, the data in this regard are limited and typically not sufficient to determine if unsuccessful dredging efforts were due to limitations in dredging, or the lack of data regarding external loads that may have persisted after the dredging was complete. An example of this situation is Lake Kasumigaura, Japan s second largest lake. Lake Kasumigaura had experienced severe eutrophication due to its shallow depth (4 m on average) and nutrient exchange between the sediment and water column. A specialized hydraulic dredge was used to dredge the fluffy top layer of the sediment. Lake water quality was not improved after the long period of dredging (Murakami, 1984 from Pollman et al., 1988). 4/10/2003 engineers & scientists 5-22

143 To assist in evaluating these data gaps on a site-specific basis, a study was conducted on behalf of the District (Reddy et al., 2002). The results of this study suggest that dredging the upper 30 to 45 cm of sediment may reduce the flux of P to the water column over the short term; however, the potential effects of long-term mixing and external loads were not considered. As such, long-term flux to the water column remains a question requiring additional research. The study did, however, recommend a focus on external load reduction, which will ultimately play a role in reducing internal loading. A bench-scale study was conducted to evaluate the potential effects of dredging Lake Müggelsee in Germany (Kleeberg and Kohl, 1999). The results and conclusions of this study are similar to those developed by Reddy et al. (2002) for Lake Okeechobee dredging the upper 30 to 50 cm of sediment may reduce internal loading for Lake Müggelsee over the short-term, and reducing the external P loading would be more effective than a dredging measure. Based on the concerns related to residual sediment remaining after dredging, the continuing contribution of P from this veneer, and the fact that the reductions in TP are primarily attributable to external load reductions, this performance measure is given a score of PM 1C: Maximize Total Suspended Solids (TSS) Reductions in the Short Term and the Long Term Over the short term, the dredging alternatives would lead to increases in TSS due to the dredging itself, CDF construction, and movement of the dredging equipment. Based on observations made during the pilot dredging study (EA, 2002b), these increases may not be significant relative to potential short-term water quality concerns. However, it should be anticipated that TSS and turbidity would be elevated in the pelagic zone to some degree during the dredging period, which is anticipated to be 15 years. Therefore, this performance measure is given a score of 2 for the short term. The predicted short-term TSS concentrations for the near-shore and pelagic zones for the dredging alternative (including the three CDF scenarios) are presented on Figure The results of the predicted concentrations of TSS in the near-shore zone for the dredging alternative and the No In-Lake Action Alternative (shown as a difference) are also presented in Figure This figure demonstrates 4/10/2003 engineers & scientists 5-23

144 that a significant difference does not exist between the No In-Lake Action and the Dredging Alternatives as it relates to predicted concentration of TSS. The same trends are also similar for TP and predicted SAV standing crop for the two alternatives (Figures 5-17 and 5-18, respectively). However, these model predictions do not include the 10 operating dredges as a source of resuspended sediment to the lake during the 15-year dredging period. In the long term, TSS concentrations would shift into equilibrium within a year or two of completion of dredging. Therefore, this performance measure is given a score of 3 for the long term PM 1D: Minimize Algal Blooms The results of the ILPM simulations presented in Figure 5-19 indicate that the frequency of algal blooms would drop below 10% before the dredging is completed (i.e., 2025), although it should be understood that this response is governed by changes in the external loading rates of phosphorus, and does not reflect any real mitigative response related to dredging. For the LOWQM model, the estimated year for the frequency of occurrence to drop below 10% is 2030 (Figure 5-20). The primary difference in the predicted model results is the variability associated with the LOWQM model where the frequency of occurrence sporadically exceeds 10% for the period of 2030 to 2060, after which the frequency of occurrence remains below 10%. This discrepancy is a direct result of the greater variance in year-to-year TP concentrations derived from sediment resuspension predicted by the LOWQM. Maintaining a TN:TP ratio of 29:1 or greater is effective for minimizing algal blooms. Model predictions of annual average TN:TP ratios are presented on Figure Model predictions for the annual frequency of algal blooms are also presented as cumulative frequency distribution plots for dredging in Figures 5-22 and The modeling results for this alternative indicate that the frequency of algal blooms decreases with time and that the target value of less than 10% is achieved between the time period of 2025 and However, the primary reason the frequency of algal blooms decreases is because of external load reduction, not because of any dredging activity. In fact, there is some concern that sediment resuspended during dredging could increase P concentrations in the water column. If these increased P 4/10/2003 engineers & scientists 5-24

145 concentrations in the water column were sustained, as might be possible over the course of the 15 year project, this could actually result in an increase in the frequency of algal blooms resulting from dredging. Therefore, this performance measure is given a score of PM 1E: Minimize Exceedances of Water Quality Standards in the Short Term and the Long Term The pilot dredging study (EA, 2002b) concluded that short-term exceedances in water quality standards, other than those related to P, are not anticipated. Although low levels of chemicals, including arsenic, are present in the sediment, they may not impact water quality during dredging. This is based on a combination of the low concentrations and the strong affinity of these chemicals for fine-grained sediment that have high organic carbon content. Elutriation tests, discussed in Section 5.2.2, presented similar conclusions relative to releases of P and heavy metals. However, the severity of the cumulative effects associated with 10 dredges operating continuously in the lake for 15 years is not known; more intensive sampling and analysis and pilot testing would be required to more clearly understand these cumulative effects. Historical lake studies indicate that, although both the water column and sediments have contained pesticide residues, levels of the pesticides appear to be decreasing as the residues breakdown in the environment (Pfeuffer, 1991). These results appear consistent with the combined expected effects of natural attenuation and diminished use of many of the pesticides that have been subsequently banned or phased out of production. It is reasonable to expect similar processes to be occurring in the sediments throughout the lake as a whole. This hypothesis could be confirmed through a more comprehensive evaluation of the sediment from the central portion of the lake. Pfeuffer and Matson (2000) present pesticide analyses from water and sediment samples collected from the lake in May A number of herbicides were detected, but there were no associated numerical criteria under Florida Class III Water Quality Standards for surface water (Chapter ); further, they did not exceed the acute or chronic calculated toxicity standards (FAC ). The highest surface water concentrations of atrazine found in this sampling event at two locations exceeded the Florida Ground Water Guidance Concentrations of 3 µg/l. Several herbicides were detected in the 4/10/2003 engineers & scientists 5-25

146 sediment at several locations, some at concentrations with the potential for impacting wildlife when compared to coastal sediment quality assessment guidelines. However, there are no corresponding freshwater sediment quality assessment guidelines. The compounds and concentrations found are typical of those expected from intensive agricultural activity. Data were flagged as estimated values, since appropriate quality control checks were not performed. These data were also collected from sampling stations located along the edge of the lake where the greatest potential for impact associated with tributary inputs would be expected. In addition, the dredge area identified for this alternative does not include these areas, as the dredging is focused in the central portion of the lake. Over the long-term, water quality standard exceedences are not expected. As discussed above, meeting the restoration target of 40 µg/l for TP would be expected to occur mainly as a result of implementing best management practices in the watershed. Because of the uncertainties associated with cumulative long-term dredging impacts and the need for additional testing, this performance measure is given a score of 3 for the short term (the 15-year dredging timeframe). Case study data show that, over the long term (10 to 15 years following dredging), lake systems would eventually return to a state of equilibrium. Since no major sediment quality issues have been identified to date, it is anticipated that water quality would not be impacted in the long term. Therefore, this performance measure is given a score of 4 for the long term PM 1F: Minimize Downstream Impacts With 10 dredges operating 24 hours per day, 7 days per week, for 15 years, it is anticipated that there could be some impacts downstream in areas of close proximity to the pelagic zone. This would be of greatest concern during the rainy season, where water may have to be released from Lake Okeechobee to prevent flooding. In this scenario, muddy dredge water could possibly be released into the St. Lucie River to the east, which is one of the closest downgradient water bodies to the pelagic zone. Therefore, during the 15 years of dredging, this performance measure is given a score of 2. The results of the water quality modeling indicate that, through a combination of external load reductions, conditions in the lake are expected to improve. As such, it is a reasonable to extrapolate 4/10/2003 engineers & scientists 5-26

147 that conditions downstream of the lake would also see some improvements in water quality; however, it should be noted that the driver for water quality improvements is external load reduction and not dredging. Therefore, dredging cannot be given credit for these improvements. For these reasons, this performance measure is given a score of Goal 2: Maximize Engineering Feasibility and Implementability PM 2A: Maximize Technical Reliability The technologies to be used in implementing the dredging alternatives are all readily available and have been used for many years and for a variety of sediments and contaminants at different locations. These technologies include: hydraulic dredging; hydraulic transport of dredged materials; settling and consolidation of sediments in CDF(s); treatment of separated water for phosphorus removal by precipitation with aluminum or iron; gravity secondary sedimentation of treated water; and habitat enhancement. Dredging could be readily conducted using any of several commercially available dredge-head types, including, but not limited to, matchbox, dustpan, plain suction, and cutterhead, as well as an innovative dredge-head, such as the Sedcut dredge recently tested during the Lake Okeechobee Pilot Dredging Study (EA, 2002b). While the goal of dredging operations is to maximize removal efficiency while minimizing water column impacts, the reality of dredging is that phosphorus-containing sediment would be resuspended and redistributed away from the point of dredging. While silt curtains may provide some degree of control for sediment resuspended during dredging, the efforts to continually move and anchor these controls may be disruptive or difficult on a large-scale site like Lake Okeechobee. This was the case for the dredging conducted at the New Bedford Harbor Superfund site, where the USACE and USEPA 4/10/2003 engineers & scientists 5-27

148 abandoned the use of silt curtains in a shallow wind-prone section of the site due the release of sediment associated with moving the silt curtains (USEPA, 1998). This experience is relevant even though the setting was not a lake and the target contaminant was not phosphorus. Challenges associated with dredging in the lake include the surface action of the wind-driven waves, as this can limit the applicability of many dredges. In the central region of the lake, large fetch allows for waves that would affect the normal operation of a dredge. Many navigational-type dredges have difficulty operating at wave heights greater than 0.5 to 1.0 m (USACE, 1983). In addition, the type of environmental dredging that would likely be used to remove sediment from Lake Okeechobee would likely be more sensitive to wave action than traditional navigational dredging operations. This is due to the fact that navigational dredges typically work in deeper water and do not have draft limitations, in contrast to the conditions in Lake Okeechobee. Dredging discharge pipelines can be constructed of either rigid or flexible pipe; rigid pipelines are much more commonly used. Rigid pipelines are typically constructed of steel, cast iron, rigid plastic, or fiberglass-reinforced plastic, and are joined by ball, sleeve, or flange joints. The pipelines can be constructed as either floating or submerged systems. For transfer to an upland treatment/disposal facility, additional piping would be laid aboveground or buried. A series of booster pumps would be required every 2 to 3 km. Pipelines and booster pumps require constant maintenance as they are prone to frequent plugging or leaking. In-Lake pipelines can present navigation disruptions in either floating or submerged systems. With as many as 10 dredges operating simultaneously, a maze of pipelines would be present. CDFs have been used for many years for separation and consolidation of sediments from navigational dredging sites. The USACE has overseen much of this construction and has issued detailed guidance for evaluating and designing such facilities (USACE, 1987). CDFs can provide economical sediment disposal for both the short and long term. Although there are some structural risks for CDFs (especially shoreline or in-lake CDFs) as they can be impacted by extreme weather events (wind and wave action during a hurricane), this risk is greatly minimized by 4/10/2003 engineers & scientists 5-28

149 the conservative approach used to design the structures. This is demonstrated by the long-term integrity and reliability of CDFs along the shores of the Great Lakes that have remained in place and performed as designed over the past 40 years. The construction of these CDFs includes a layer of rock armor on the side walls of the CDFs to prevent the erosion of the dikes due to wind-driven waves that are significant in the Great Lakes. Phosphorus removal using aluminum or iron salts has been applied to municipal wastewaters for a number of years (USEPA, 1987). Phosphorus removal from decanted dredge slurry water was evaluated in both bench-scale testing (EA, 2002a) and along with the pilot dredging project (EA, 2002b). These studies have indicated that ferric chloride applied at Fe:P molar ratios of 100:1 to 200:1 with settling times of 3 hours or less can produce effluents with total P less than 40 µg/l and often less than 10 µg/l. In addition to typical CDF design features, the roots of the wetland plants within the completed CDF would help to keep the sediment anchored in place. The plants would use the nutrient-rich soil, and in this manner, recycle the high nutrient content from the lake s sediment into plant form and ultimately back into the food web, effectively keeping it out of the lake. Based on the above, this performance measure is given a score of PM 2B: Maximize Technical Scalability The dredging rates of 150 m 3 /hr to 200 m 3 /hr per dredge can readily be accomplished using hydraulic dredges ranging in size from 20 to 30 cm. These are dredge sizes that are readily available. Integrating the simultaneous efforts of 10 dredging crews introduces a level of complexity beyond the norm for most environmental dredging jobs and proper management and planning of logistics would be essential. Many navigational dredging projects far exceed the scope of dredging 12 million m 3 per year. A rate of 2,000 m 3 /hr can be accomplished by a single 76-cm (30-in) cutterhead dredge. 4/10/2003 engineers & scientists 5-29

150 The dredging alternatives would generate dredge slurry that would be transferred to the CDF(s) at a rate of 125 to 136 cubic meters per minute (m 3 /min) total from 10 dredges during an 18-hr day. Individual dredge pipeline sizing on the order of 23 to 30 cm is anticipated. For collecting and pumping to an upland facility, dual pipelines on the order of a 50-cm diameter are anticipated. None of these sizes are at a scale that is out of the ordinary. The CDF(s) could be constructed at a number of potential locations, including along the shoreline of the lake, as island(s) within the lake, or within an undeveloped upland area such as former agricultural land or an abandoned quarry. CDFs are often constructed using a combination of earthen dikes, barrier systems, and cover systems that isolate the sediment from the aquatic environment. CDFs have been constructed in the wet as diked containment facilities within a water body, or in the dry as upland earthen diked facilities on shorelines. The shoreline structures are often constructed partially on land to provide land-based access and to facilitate beneficial re-use. For example, CDFs have been used to construct docking facilities, airports, and habitat enhancement projects. In fact, as of the early 1980s, over 130 marshes had been created using dredged sediment (USACE, 1983). Island CDFs within a lake could be constructed in a manner to facilitate desirable hydraulic circulation by minimizing the future effects of wind-driven waves on phosphorus-containing sediment that has accumulated in the lake over time (i.e., function as breakwaters). Such a CDF was constructed in Lake Ketelmer, Holland, a 2,800-ha lake with a variety of contamination issues (Roukema et al., 1998). This 1 km diameter in-lake CDF has a design storage capacity of 21 million m 3 (Palermo and Averett, 2000), where the sediments would be placed following dredging. This area will eventually be converted into a combination of recreational sand islands and noncultivated nature reserves. The scale of the CDF(s) for Lake Okeechobee would be similar in magnitude to the Craney Island Dredged Material Management Area, a 1,012-ha (2,500-acre) confined dredged material disposal site located near Norfolk, Virginia. These sediments are dredged from the channels and ports in the areas of Norfolk, Portsmouth, Chesapeake, Newport News, and Hampton. Construction of Craney Island was completed in 1957, and, since that time, it has received over 153 million m 3 (200 million cy) of sediment. With square dimensions of approximately 3.2 km (2 mi) per side, it was originally designed 4/10/2003 engineers & scientists 5-30

151 to contain 76 million m 3 and last until 1980, but use of several innovative approaches allowed greater capacity. Additional expansion is expected to accommodate an additional 76 million m 3 (100 million cy) of dredged material. Additional details are available at: The Baltimore District of the Corps of Engineers and the Maryland Port Administration developed a CDF to connect Hart and Miller Islands in the Chesapeake Bay near Baltimore Channel, Maryland. The project developed a 445 ha area that is now used as a recreational site. A riprap dike was used for protection. Fresh marsh vegetation of the site was through natural colonization. The Hart-Miller Island State Park is part of the largest dredged material containment/island reclamation project ever undertaken in Maryland. The project has been designed and managed to protect existing wetlands, forest habitat, and wildlife on Hart Island. It has enhanced recreational opportunities for people by providing a 1 km beach reconnecting Hart and Miller Islands. The USACE is also developing Poplar Island, which has eroded from an area of 445 ha in 1847 to its current size of 2 ha. The Baltimore District and the Maryland Port Administration are rebuilding the island s eroded wetlands and wildlife habitats by installing sand, stone, and rock dikes to ultimately contain 29 million m 3 of clean sand and silt dredged from the Chesapeake Bay's shipping channels. This is expected to restore Poplar Island to its previous size of 445 ha. After primary separation of solids in the CDF(s), water would be transferred for treatment and secondary sedimentation at a rate of 106,000 to 117,000 m 3 /day. While this is considerably more than usual for a dredging project, it is a quantity well within the range handled by many municipal water and wastewater treatment facilities that employ similar sedimentation technologies for treatment. Laboratory testing of settling/sedimentation and consolidation would be necessary to aid in designing the dimensions of the CDF and settling areas. Design considerations include the volume of material to be disposed, dredging and transport methods, operating plan, physical properties of materials, and target water effluent quality. Capacity considerations must also take into account consolidation of solids within and under the CDF due to additional loading and desiccation of solids. 4/10/2003 engineers & scientists 5-31

152 Based on the above, this performance measure is given a score of PM 2C: Maximize Equipment and Material Availability Dredging equipment is owned by a number of contractors who specialize in both navigational and environmental dredging. Several internet sites also illustrate that used dredging equipment is readily available. For example, see: or While finding the availability of 10 dredges to be devoted to one project for 15 years is not the norm, there are likely many contractors who would acquire the specified dredging equipment for the security of a long-term contract. Bidding could be tailored for any number of yearly intervals from 1 to 15 or any number of years between. Similarly, locating the total quantities of dredge slurry pipelines may be challenging. Ten dredge crews operating at representative distances from an island CDF would require on the order of 120 km of 23 to 30 cm diameter pipelines. Slightly more piping would be required for a shoreline CDF. For transfer to an upland facility, an additional 20 km or more of 50 cm diameter pipelines could be required to transport dredge slurry to the CDF and convey treated waters back to the lake. CDFs with wetlands disposal are implementable for Lake Okeechobee and would typically be constructed of earthen dikes, with a water collection and spillway system. Depending on the hydraulic forces associated with wave action, the dikes may need to be armored. Construction of dikes would require on the order of 6 to 8 million m 3 (8 to 11 million cy) of sand, gravel, and stone. A total of 58 suppliers of sand and gravel and 37 suppliers of crushed stone are located within 90 miles of the lake. Once the perimeter dikes are constructed, dredged material can be placed in the CDF and managed to facilitate sediment dewatering (consolidation and settlement), as well as water treatment. When the sediment is approximately 90% to 95% consolidated, interior features such as trenches, channels, and mounds may be constructed for the establishment of the wetland system. The dikes can then be 4/10/2003 engineers & scientists 5-32

153 breached at select locations, allowing hydraulic action at the site. These features can be constructed with conventional earthmoving equipment. Interior dikes are typically built within the CDF to create separate compartments for material containment. Once an individual compartment is filled, filling of a new compartment can begin. In addition, if consolidation of material provides sufficient new capacity, a previously filled compartment may be available for addition of new material. Under this scenario, multiple compartments could be in use concurrently. Lastly, to minimize areal extent, dikes in the CDF could be raised above the initial height at a later date, provided the foundation has adequate strength. Construction of a CDF is typically done with the assistance of traditional earthmoving equipment such as bulldozers, backhoes, and other readily available equipment and equally common building materials. Construction of the perimeter dikes typically incorporates native or imported soil in combination with other materials (as necessary to achieve the required structural properties). If needed, the earthen structure can be lined with either a clay or geotextile liner material. Alternative designs for CDFs include the use of former farmlands such as the Lake Trafford, Florida dredging project or the use of abandoned mines or quarries, as is being done in Pennsylvania. The principal considerations for CDF implementation at Lake Okeechobee are the volume of sediment potentially requiring containment and siting of the facilities. Dredging of the mud volume (161 to 177 million m 3 ) would require a significant volume of storage within a CDF. After dewatering and consolidation, a single CDF accommodating this volume would be roughly 5,600 meters long, 1,900 meters wide, and 7 meters high. It is possible to raise the dike heights in the CDF once the dredged material has undergone sufficient consolidation, thereby reducing space requirements and increasing storage capacity. Confirmation of soil foundation conditions would be necessary prior to siting, and CDF operations would be designed to prevent impacts to area aquifers. 4/10/2003 engineers & scientists 5-33

154 Water collection systems are an integral part of a CDF. Water derived from the dredged sediments, either via a weir or subsurface drainage, must be collected, and, if necessary, treated before discharge to a receiving water body. Interior trenches within the CDF are another means of collecting water. Water management would be an important component of a CDF for a Lake Okeechobee application, as the re-release of phosphorus into the lake must be minimized. Subsurface seepage from CDFs into adjacent aquifers is a possibility and must be considered when siting and designing the CDF and during design of the water collection system. Precipitation of phosphorus from the separated dredge slurry water would require on the order of 13,000 tonnes per year of ferric chloride (60% crystal) or 200,000 tonnes over the 15-year duration. This is equivalent to around 150 rail cars per year for ferric chloride deliveries. Availability of this quantity should not be critical. Aluminum sulfate could also be substituted for the same purpose. Based on the above, this performance measure is given a score of PM 2D: Maximize Permanence Dredging is a permanent remedy to the extent that it removes a large volume of sediment and the associated mass of TP. However, what is more important is the surface sediment TP concentration that will remain after dredging. Based on the case study literature and the modeling conducted for this project, the achievement of water quality standards is primarily due to reductions in external loads and not dredging. The CDF structures would be armored with appropriately sized stone/rock to withstand wind and wave erosive forces associated with design-frequency storms. It is assumed that use of accepted models or design procedures would minimize uncertainties associated with permanence of the CDF exterior walls. Design of exposed slopes would be based on USACE guidance presented in the Shore Protection Manual (USACE, 1995). 4/10/2003 engineers & scientists 5-34

155 The permanence of the dredging remedy with regard to residual surface concentrations of TP will be influenced principally by the effectiveness of the implementation of best management practices in the watershed. If external source control is ineffective, the dredged surfaces will be recontaminated. Based on the above, this performance measure is given a score of PM 2E: Minimize On-Shore Land-Use Needs and Conflicts Dredging would require several acres of on-shore land for equipment access, docking, material deliveries, parking, and trailers or buildings for management and administration. Similar land-side needs are associated with CDF and water treatment facilities. For the upland CDF scenario, additional land (or rights-of-way) would be needed for pipelines and booster pumps to and from the lake and CDF. The availability of land or shoreline for siting a CDF would impact the location considerations. Other considerations would include the trade-off between lost open-water habitat and the benefit of creating new wetland habitat, the long-term role that island CDFs may play in minimizing sediment resuspension and phosphorus mobilization over the long term following completion of the dredging project, and the high value of the habitat within the littoral zone along the western shore of the lake. The remainder of the shoreline supports a variety of agricultural uses such that a shoreline CDF may have to be constructed mostly within the water to minimize the taking of land. CDFs can be feasibly implemented for Lake Okeechobee as they have been demonstrated as effective for disposal of large volumes of dredged sediments. CDFs have been used extensively for storage of sediments dredged from the Great Lakes and, are one of the most widely used technologies for managing contaminated sediments (Palermo and Averett, 2000). Since the 1960s, approximately 50 CDFs have been constructed around the Great Lakes. Two-thirds of these CDFs are wet CDFs (built within the lakes), and one-third upland ( dry ) facilities. The largest capacity of any single CDF was 3 million cy, and several hundred hectares in size (USEPA, 1994). The largest CDFs have been constructed in the Netherlands (Palermo and Averett, 2000), including the 21-million-m 3 CDF Ijsselog site in Lake Ketelmer and another large CDF at the Slufter site. 4/10/2003 engineers & scientists 5-35

156 Wetland disposal areas could be feasibly implemented at Lake Okeechobee, since they have been shown at other sites to effectively handle disposal of large volumes of dredged sediments and the technology and techniques to carry out a successful wetlands disposal project are well established. The three major dredged material wetland projects (Sonoma Baylands, Atkinson Marsh, and Poplar Island) used several million m 3 of dredged material to restore and create the wetland habitats (Hayes et al., 2000). Feasibility considerations must include siting of the facility in an area that is acceptable to the public and citizen/interest groups. The use of an abandoned quarry or mine for the upland disposal of sediment may have applicability to the sediment from Lake Okeechobee. This disposal method is currently being used in Pennsylvania for approximately 6 million tons of mud dredged from the New York/New Jersey (NY/NJ) Harbor (NRPA, 2001). However, it would be necessary to conduct a survey of abandoned quarries in the South Florida region to further develop this approach. CDFs often offer an attractive, cost-effective method of disposal for dredged material. If properly located and constructed, they can effectively isolate the dredged sediment from the surrounding environment. CDFs minimize the potential re-handling of sediment as they can serve multiple purposes in addition to sediment disposal (dewatering and water treatment). The use of onsite CDFs can also minimize the distance that the dredged sediment is transported due to their proximity to the dredged area. This is especially true for island CDFs that are located within the water body itself. Based on the above, this performance measure is given a score of PM 2F: Satisfy Permitting Requirements Permits and approvals would be required for dredging, siting, and building the CDF(s), and for operating facilities and treating the associated water and discharging it back to the lake or other surface water. Federal, state, and local environmental, operational, and safety permits as well as approvals and certificates may be required from the following agencies: FDEP, USACE Jacksonville District, 4/10/2003 engineers & scientists 5-36

157 USEPA Region IV, U.S. Coast Guard, South Florida Water Management District, Martin and/or Okeechobee counties, FWC, and US Fish and Wildlife. The issues and concerns of the above referenced agencies would need to be addressed within a comprehensive ERP application. The application and approval process would be led/managed either by FDEP or the USACE for a dredging project. The siting and design requirements for a CDF may need to comply with certain provisions in Chapter of the FAC. However, the very nature of CDFs as sediment containment structures built near or within the water are inconsistent with some aspects of these regulations (i.e., the facility must be sited a minimum of 200 ft away from the lake and outside the 100-yr floodplain). The requirements of applicable wetland regulations under the Clean Water Act are more relevant to this application and would play a large role in the siting and permitting processes. In either case, it would be necessary to design and operate the facility in a manner to protect the aquatic resources of the lake, as well as area groundwater. All of these issues would be determined during the course of a lengthy and involved permitting process. Given the large number of approvals required under the ERP application, the potential for conflict between agencies responsible for the water- and land-side aspects of this project, and the potential for permit challenges, this performance measure is given a score of Goal 3: Maximize Cost-Effectiveness PM 3A: Minimize Construction Costs The total cost to implement the dredging alternatives ranges from $3.2 billion to $3.5 billion depending on the location and type of sediment disposal facility. The total cost to implement dredging with two 4/10/2003 engineers & scientists 5-37

158 island CDFs is $3.50 billion, compared to $3.21 billion for dredging with one shoreline CDF and $3.37 billion for dredging with one upland CDF. NPV is used to evaluate construction and operating expenditures that occur over different periods of time by discounting all future costs to a common base year. This allows comparisons on the basis of a single figure, which represents the amount of money that, if invested in the base year, would be sufficient to cover all costs over the planned life of the project. Using a beginning-of-year discount rate (adjusted for inflation) of 5.8 percent, the 2002 Net Present Values for the three dredging alternatives are $1.24 billion (Alternative 3A), $1.14 billion (Alternative 3B), and $1.19 billion (Alternative 3C). Cost estimate summaries for these three alternatives are presented in Tables 5-3, 5-4, and 5-5, respectively, while details are presented in Appendix E. 4/10/2003 engineers & scientists 5-38

159 Table 5-3 Conceptual Cost Estimate - Alternative 3A - Hydraulic Dredging to Two Island CDFs Summary Estimate Item Estimated $/cy Net Present $/cy Description No. Amount Dredged Value Dredged 1. Dredging $1,618,100,000 $7.70 $526,300,000 $ Dredged Slurry Transport to Upland CDF $0 $0.00 $0 $ Confined Disposal Facility $735,200,000 $3.50 $297,400,000 $ Water Treatment $180,200,000 $0.86 $59,100,000 $ Operational Monitoring and Construction Management $95,900,000 $0.46 $33,000,000 $0.46 DIRECT CAPITAL COSTS SUBTOTAL: $2,629,400,000 $12.52 $915,800,000 $ Design and Indirect Capital Costs $815,900,000 $3.88 $276,900,000 $1.32 TOTAL CAPITAL COSTS: $3,445,300,000 $16.40 $1,192,700,000 $ Annual Long-Term Operation, Maintenance and Monitoring (OM&M) $15,620,000 PRESENT WORTH OF OM&M (50 Yrs. at 5.8%): $52,200,000 $0.25 $52,200,000 $0.25 TOTAL COST OF SCENARIO: $3,497,500,000 $1,244,900,000 TOTAL COST PER CUBIC YARD OF SEDIMENT DREDGED: $16.65 $5.93 Notes: 1. Dredging conducted by 10-inch cutterhead dredge (10 crews), removing total volume of 210,074,000 cy over a period of 15.0 years. 2. Dredged Slurry Transport required for some Upland CDF or Beneficial Reuse Scenarios. 3. Confined Disposal Facilities would occupy an area of approximately 6,350 acres. CDF would be constructed to a height of 24 feet, with a final consolidated sediment height of 22 feet. 4. Water treatment operations would consist of preliminary sedimentation followed by phosphorus precipitation, flocculation, and secondary sedimentation. Facilities to handle water flow rates of 28 million gallons per day (MGD) would be required. 5. Operational Monitoring and Construction Management includes $78,337,000 for construction management and $17,597,000 for bathymetric surveys, engineering oversight, and confirmation sampling and analyses. 6. Design and Indirect Capital Costs include 30% contingencies ($788,820,000), engineering, permitting and access ($27,112,000). 7. Annual Long-Term OM&M includes sampling and analyses of sediments and water columns at 20 stations annually for 50 years, as well as observation and maintenance of CDFs, and OM&M contingencies. 4/10/2003 engineers & scientists 5-39

160 Table 5-4 Conceptual Cost Estimate - Alternative 3B - Hydraulic Dredging to Shoreline CDF Summary Estimate Item Estimated $/cy Net Present $/cy Description No. Amount Dredged Value Dredged 1. Dredging $1,620,900,000 $7.09 $527,200,000 $ Dredged Slurry Transport to Upland CDF $0 $0.00 $0 $ Confined Disposal Facility $542,000,000 $2.37 $218,400,000 $ Water Treatment $164,300,000 $0.72 $53,900,000 $ Operational Monitoring and Construction Management $84,900,000 $0.37 $29,200,000 $0.37 DIRECT CAPITAL COSTS SUBTOTAL: $2,412,100,000 $10.55 $828,700,000 $ Design and Indirect Capital Costs $747,100,000 $3.27 $253,000,000 $1.11 TOTAL CAPITAL COSTS: $3,159,200,000 $13.82 $1,081,700,000 $ Annual Long-Term OM&M $16,610,000 PRESENT WORTH OF OM&M (50 Yrs. at 5.8%): $55,500,000 $0.24 $55,500,000 $0.24 TOTAL COST OF SCENARIO: $3,214,700,000 $1,137,200,000 TOTAL COST PER CUBIC YARD OF SEDIMENT DREDGED: $14.06 $4.97 Notes: 1. Dredging conducted by 10-inch cutterhead dredge (10 crews), removing total volume of 228,597,000 cy over a period of 15.0 years. 2. Required for some Upland CDF or Beneficial Reuse Scenarios. 3. Confined Disposal Facility would occupy an area of approximately 6,760 acres. CDF would be constructed to a height of 24 feet, with a final consolidated sediment height of 22 feet. 4. Water treatment operations would consist of preliminary sedimentation followed by phosphorus precipitation, flocculation, and secondary sedimentation. Facilities to handle water flow rates of 31 MGD would be required. 5. Operational Monitoring and Construction Management includes $67,350,000 for construction management and $17,599,000 for bathymetric surveys, engineering oversight, and confirmation sampling and analyses. 6. Design and Indirect Capital Costs include 30% contingencies ($723,630,000), engineering, permitting and access ($23,450,000). 7. Annual Long-Term OM&M includes sampling and analyses of sediments and water columns at 20 stations annually for 50 years, as well as observation and maintenance of CDFs, and OM&M contingencies. 4/10/2003 engineers & scientists 5-40

161 Table 5-5 Conceptual Cost Estimate - Alternative 3C - Hydraulic Dredging to Upland CDF Summary Estimate Item Estimated $/cy Net Present $/cy Description No. Amount Dredged Value Dredged 1. Dredging $1,625,300,000 $7.01 $528,600,000 $ Dredged Slurry Transport to Upland CDF $101,700,000 $0.44 $33,500,000 $ Confined Disposal Facility $539,400,000 $2.33 $217,100,000 $ Water Treatment $166,200,000 $0.72 $54,600,000 $ Operational Monitoring and Construction Management $90,900,000 $0.39 $31,300,000 $0.39 DIRECT CAPITAL COSTS SUBTOTAL: $2,523,500,000 $10.88 $865,100,000 $ Design and Indirect Capital Costs $782,500,000 $3.37 $265,300,000 $1.14 TOTAL CAPITAL COSTS: $3,306,000,000 $14.25 $1,130,400,000 $ Annual Long-Term OM&M $17,990,000 PRESENT WORTH OF OM&M (50 Yrs. at 5.8%): $60,200,000 $0.26 $60,200,000 $0.26 TOTAL COST OF SCENARIO: $3,497,500,000 $1,190,600,000 TOTAL COST PER CUBIC YARD OF SEDIMENT DREDGED: $14.51 $5.13 Notes: 1. Dredging conducted by 10-inch cutterhead dredge (10 crews), removing total volume of 231,930,000 cy over a period of 15.0 years. 2. Required for some Upland CDF or Beneficial Reuse Scenarios. 3. Confined Disposal Facility would occupy an area of approximately 6,860 acres. CDF would be constructed to a height of 24 feet, with a final consolidated sediment height of 22 feet. 4. Water treatment operations would consist of preliminary sedimentation followed by phosphorus precipitation, flocculation, and secondary sedimentation. Facilities to handle water flowrates of 31 MGD would be required. 5. Operational Monitoring and Construction Management includes $73,253,000 for construction management and $17,599,000 for bathymetric surveys, engineering oversight, and confirmation sampling and analyses. 6. Design and Indirect Capital Costs include 30% contingencies ($757,050,000), engineering, permitting and access ($25,418,000). 7. Annual Long-Term OM&M includes sampling and analyses of sediments and water columns at 20 stations annually for 50 years, as well as observation and maintenance of CDFs, and OM&M contingencies. Estimated costs to implement the dredging alternatives were highly dependent on sediment property data and estimates of sediment volumes. In particular, the extent and depth of the mud zone (where the sediment layer exceeded 10 cm deep) was used to define a practical limit of dredging. The chemical characteristics (phosphorus and heavy metals) and geotechnical properties (bulk density, particle sizes, moisture content, and shear strength) of sediment in the mud zone are reasonably well defined. These data are supplemented by bench-scale treatability testing and a pilot dredging project, which further helped to limit the uncertainties associated with the dredging and treatment cost estimates. 4/10/2003 engineers & scientists 5-41

162 The conceptual selection and sizing of facilities for dredging, transport, treatment, and disposal of water and sediment residuals is supported by an extensive technical literature and history of both navigational and environmental dredging at other sites. The greatest degree of uncertainty is introduced by the magnitude of the dredging program, which would exceed the size and duration of any single environmental dredging program ever undertaken. On the other hand, the 177 million m 3 of sediment that would be dredged from Lake Okeechobee over a 15-year period represents less than 7% of the dredging that takes place throughout the U.S. on an annual basis. The three sub-alternatives evaluated alternative placement of CDFs to minimize the amount of dredging and space of the disposal (CDF) site. Use of the CDF as area for final settling of treated water also helps to minimize the construction costs. However, the construction costs associated with the three variations of the dredging alternatives are significantly greater than the construction costs of Alternatives 1 and 2. Based on the above, this performance measure is given a score of PM 3B: Minimize Operation and Maintenance Costs The Dredging with CDF Alternative is fairly labor-intensive. Because of the extended duration of dredging (15 years), the costs for dredging and water treatment could be considered part of the O&M costs. For this evaluation, however, they were considered part of the direct construction costs. After completion of dredging and closure of the CDF, there would also be long-term maintenance and monitoring activities. The estimated costs also include quantification of NPV using procedures and discount rates recommended by the USEPA (USEPA, 2000). This approach assists in evaluating the tradeoffs between alternatives with different balances of construction versus O&M costs. The NPV (year 2002) O&M costs for the dredging alternatives are $52.2 million (Alternative 3A), $55.5 million (Alternative 3B) and $60.2 million (Alternative 3C). 4/10/2003 engineers & scientists 5-42

163 O&M costs associated with the three variations of the dredging alternatives are significantly greater than the O&M costs of Alternatives 1 and 2. This performance measure is given a score of PM 3C: Maximize Benefits (Material Reuse) The island or shoreline variations of the dredging alternatives produce a side benefit of creating additional terrestrial and wetland habitats and, potentially, additional littoral zones within the lake. This alternative is given a score of Goal 4: Maximize Environmental Benefits PM 4A: Maximize Benefits to Wetland Vegetation in Littoral Zone Although engineering controls would be in place to minimize suspended sediment in the pelagic zone from reaching the littoral zone, the lake s pelagic zone sediments resuspended during dredging have the potential to migrate to the littoral zone over the 15-year dredging period. If this occurred, there could be negative impacts on the littoral zone due to increased turbidity and decreased light transmission. The impacts would be most harmful during storm events, where recently suspended sediment from dredging could be easily transferred to the littoral zone via lake currents and heavy wave action. Since the modeling shows that improvements in water quality are primarily due to reductions in external loads and since there is the potential for a decrease in water quality in the littoral zone during dredging, this performance measure is given a score of PM 4B: Maximize Benefits to Submerged Aquatic Vegetation (SAV) Although engineering controls would be in place to minimize suspended sediment from reaching the littoral zone where the valued SAV occurs, the lake s pelagic zone sediments would essentially be continually re-suspended for 15 years until dredging was completed. This would be expected to ultimately have some negative impact on SAV. The impacts would be most harmful during storm events and wind events where recently suspended sediment during dredging could be easily transferred to the littoral zone via lake currents. The effects of this would likely be increased turbidity and decreased light transmission. Further, as the modeling results for dredging show, there would be 4/10/2003 engineers & scientists 5-43

164 minimal water quality improvements anywhere in the lake, since post-dredge flux of P into the water column would persist from residual sediment left in place after dredging. This performance measure is given a score of PM 4C: Maximize Benefits to Fish and Aquatic Invertebrate Communities The Dredging with CDF Alternative achieves the algal bloom threshold earlier than the No In-Lake Action Alternative, but somewhat later than the Chemical Treatment Alternative. However, the dredging process itself would destroy the benthic ecosystem (over the short term) in the area of dredging, and could impact the water column community in the vicinity of the dredging operation in the short term. Nevertheless, recovery due to sediment drift from adjacent areas will be an ongoing occurrence and should contribute to a fairly rapid reestablishment of the benthic community. Thus, this alternative is ranked 2 over the short term, because the relative benefits are not great, and there is a high probability (certainty, in the case of benthic communities) of negative impact. Over the long term, the benthic communities would recolonize and the water column would clear (after dredging). As a result, the performance measure is given a score of 3 over the long term PM 4D: Minimize Negative Impacts to the Manatee Manatee currently find suitable habitat in the lake, and present SAV levels (a primary food source) support an active population. There is not, however, any evidence that SAV is a limiting factor for manatees in the lake. The Dredging with CDF Alternative yields marginal benefits. While active dredging has the potential to impact manatees by physical contact and/or noise or other disturbance, it is unlikely that dredging would proceed in any locations or times where manatees are present. There is little potential for benefit, and while there is some potential for impact, this is likely to be low. Thus, this performance measure is given a score of 3. 4/10/2003 engineers & scientists 5-44

165 PM 4E: Minimize Negative Impacts to the Alligator Alligators presently find suitable habitat and trophic resources in the lake. There is no evidence that any conditions related to phosphorus levels are limiting to alligators. The Dredging with CDF Alternative would involve the direct destruction of large areas of lake bottom habitat, but would not impact the littoral zone or SAV. Thus, there is little potential for either benefit or impact to alligators, and this performance measure is given a score of PM 4F: Minimize Negative Impacts to the Okeechobee Gourd The Okeechobee Gourd is not an aquatic species, although its primary habitat is presently strongly associated with Torrey muck soils that formed in formerly extensive pond apple forests around the lake (FWC personal communication, 2002). The dredging alternative, at this stage of development, does not yield any direct benefits to Okeechobee Gourd, nor does dredging have potential for negative impacts (assuming that dredging itself, facility siting, and on-shore activities are required to avoid known Gourd locations). It should be noted that the Dredging with CDF Alternative has some potential to yield benefits to the Gourd if appropriate beneficial re-use is made of dredged material. The known association of the Okeechobee Gourd with lake-edge habitat and disturbed sites such as alligator nests means that active management of redistributed dredged materials on new islands or in a shoreline CDF could potentially provide targeted habitat for this species. Based on the above summary, this performance measure is given a score of 3. 4/10/2003 engineers & scientists 5-45

166 PM 4G: Minimize Negative Impacts to the Snail Kite and Wading Birds The snail kite and aquatic wading birds depend on functional littoral habitat (FWC personal communication, 2002). The primary benefits associated with phosphorus management would be the enhancement of this habitat. Transport or migration of sediment re-suspended during dredging (which could be especially pronounced during storm events) could result in turbid water and decreased water clarity in the littoral zone. This could impair the snail kite s ability to see the apple snail, which makes up almost 100 percent of its diet. The Dredging with CDF Alternative has little incremental benefit relative to the No In-Lake Action Alternative other than the creation of additional littoral zones along the edge of the CDFs and the potential for the formation of additional littoral zones along the eastern shore of the lake. However, dredging might indirectly impact the littoral zone on which the birds depend, so this alternative could have some negative impact. For these reasons, this performance measure is given a score of Goal 5: Maximize Socioeconomic Benefits This goal evaluation includes a discussion of the socioeconomic impacts of dredging with sediment disposal in a CDF alternative. A separate write-up has not been included for each of the three potential CDF locations (i.e., in-lake, near-shore and upland). Rather, the potential socioeconomic implications of all three are discussed under each performance measure PM 5A: Maximize Regional Socioeconomic Benefits The construction operations to support this alternative over a 20-year period would be substantial. These activities include the dredging operations and the efforts to construct any of the CDFs. Any of the approaches (in-lake, shoreline, or upland) would require significant quantities of sand and gravel to build the dike walls. The dredging activities would include the presence of up to 10 dredges and the 4/10/2003 engineers & scientists 5-46

167 associated network of booster pumps and hydraulic transport pipelines. The dredging would also occur 24 hours per day, 7 days per week. It addition, the CDFs would occupy over 2,700 ha, depending on their configuration. The area to be dredged is approximately one-third of the aerial extent of the lake, primarily in the center region. Dredges are large and slow moving, but would be operated 24 hours per day and would be connected to the CDF by large network of pipelines. The pipelines would average 25 cm in diameter and would extend for distances as short as a few hundred yards to as long as 40 km (25 miles). The average pipeline distance is estimated to be 15 km (9 miles). In addition, each pipeline would require a booster pump approximately every 1 to 3 km. All of this infrastructure would be serviced from a staging area estimated to be 4 ha in area. As presented in the detailed description of the dredging alternative and Figures 5-1 through 5-3, the potential location for the in-lake CDF would be in the deepest part of the pelagic zone, the potential location for a shoreline CDF would be along a portion of the eastern shore of the lake that would not impact the SAV beds, and a potential location for the upland CDF is again on the east side of the lake, in a presently undeveloped area. Socioeconomic Problems While the concept of 10 dredges feeding 10 pipelines, each with five booster pumps (50 pumps in all), operating 24 hours per day, seven days per week, sounds like it would create a lot of clutter and noise, the reality is that most of the operating equipment would be a significant distance from land, and the negative impacts would likely be more of a perception than a reality. Practically speaking, very few of the area s residents live on or near the shore. Further, recreational activities on the lake make up a very small portion of the lake s economic base. The greatest effect would come as a diminished quality of life for those residents who use the lake often for recreational activities. This would be especially true for those who frequent the dredging area for recreational activities (due to the disruption of dredge and pipeline operations). The creation of the large CDF structures may also create aesthetic issues as the current topography in the area is quite flat, and the CDF structures would provide a stark contrast to the current land form. 4/10/2003 engineers & scientists 5-47

168 The 4-ha staging area would generate some vehicular traffic on the area s roads, but the traffic would consist almost entirely of passenger cars and light trucks. Truck or rail car deliveries might be required for CDF berm soils, rocks, water treatment chemicals, fuel, and CDF cover plantings. If it is assumed that one in five of the estimated workers rides with a co-worker, and that 10 service vehicles per day visit the staging area, then approximately 600 trips per day would be generated by the staging area at the height of its operation (285 employee vehicles and 10 service vehicles arriving and leaving daily). This load could be spread over a wider area if additional parking only areas for the on-dredge employees were provided several miles from the staging area. There could be some environmental damage and spilling of petroleum-based materials at the staging area, but measures can be taken to attenuate those situations as they happen, and, at the end of the 15- year dredging operation, the site can be returned to its original state. Socioeconomic Benefits The primary benefit of dredging is an increase in jobs. The dredges and staging area are estimated to require well over 300 people per day. An approximate economic benefit for these jobs can be calculated using SIC 17-construction-special trade as a proxy for activities on the dredges and SIC-16 heavy construction (except general contractors) as a proxy for activities at the staging area. An example of this benefit is outlined below using 2001 data from Appendix D and the in-lake CDF. The Lake Rim s average sales per employee (in SIC 17) was $148,448, and the average sales per employee for SIC 16 was $101,124. Multiplying these figures by the estimated number of new jobs suggests an increase in the region s economic activity of $45,749,520 annually for 15 years. SIC 17-construction-special trade 240 $148, $35,637, SIC 16-heavy construction 100 $101, $10,112, That figure represents an increase of 1.2% in the region s total annual economic activity for In summary, the negative aspects of dredging would be interruptions in some recreational activities, aesthetic impacts, and perceived increases in clutter and noise on the lake. These issues are balanced by a 15-year increase of approximately 340 local jobs and an annual economic boost of $45.7 million 4/10/2003 engineers & scientists 5-48

169 for 15 years. As a result, this performance measure is given a score of 4. While the problems are not significant, the over benefit to the local economy is proportionately small for a $3 billion dollar project PM 5B: Minimize Environmental/Social Inequities Social inequities are measured by how evenly the positive and negative impacts are distributed. As a practical matter, this is best evaluated by the economic and social characteristics of the locations where the alternatives are implemented. As described in the Appendix D, the Lake Rim s characteristics make evaluating environmental and social inequities a straightforward task. The economic conditions are strongest on the western half of the Lake Rim, and they weaken toward the eastern rim. Similarly, the economies of the western cities are more evenly distributed across economic sectors than are those of the eastern cities. Ethnically speaking, a large majority of the small number of American Indians in the region live on the northwest rim. Similarly, a large proportion of the sizable African-American population living in the region lives on the southeastern rim. The equally large population of people of Hispanic cultural heritage is relatively evenly spread throughout the region, with a slightly higher concentration in the east than in the west. The northeastern lake shore is largely uninhabited; the largest city in the area, Indiantown, is located about 13 km from the Lake Rim and is connected to the lake only by a secondary road. The Hispanic population in Indiantown is the highest percentage share of any city in the subject area. The city of Okeechobee, located on the northernmost shore of the lake, is the largest and most stable economic area in the region. Although it has the highest percentage share of American Indians in the region, the population concentration is located mostly to the west of Okeechobee. That population would have the farthest to go to gain from jobs created by this alternative, unless a secondary employee parking area was constructed nearby. 4/10/2003 engineers & scientists 5-49

170 To the south of Indiantown, on the lake shore, is the Pahokee/Canal Point area, one of the least stable areas economically and the location of one of the highest percentage shares of African-Americans. While dredging would take place in the central portion of the lake, a preliminary evaluation suggests that from an engineering perspective, the sediment disposal facilities (in-lake, shoreline, or upland) would be most cost-effectively constructed towards the eastern portion of the Lake Okeechobee. Doing so eliminates the potential to impact the existing SAV beds and avoids impacts to area infrastructure. However, placing these facilities in this region may also unevenly allocate a large proportion of the project benefits to area residents through jobs created. To summarize, economic benefits would likely accrue to all three basic ethnic and cultural minority groups, but probably least so to the American Indians. On this basis, this performance measure is given a score of PM 5C: Maximize Community Acceptance Community acceptance of dredging and sediment disposal in a CDF to improve water quality in Lake Okeechobee could likely be low. This based on the combination of high costs to construct the project, and the limited improvements in water quality that are predicted to occur as compared to those attributable to reductions in external P loading. While dredging is relatively common, the large volume of sediment that would be removed under this alternative and the estimated $3+ billion dollars to construct the project will generate significant attention, especially due to the potential impact on taxes or other fees. Relative to the different CDF approaches, there may be some environmental benefit associated with the in-lake CDF approach (additional littoral zones and wetland areas). However, looking at the complete system, these potential gains would have to be offset by the loss of flood storage capacity and aquatic habitat, as well as the long-term maintenance costs for the facility itself. These tradeoffs also exist for the other CDF locations where gains in one area may be offset by losses in another. For example, the upland CDF approach avoids the taking of aquatic habitat, but may infringe on the habitat 4/10/2003 engineers & scientists 5-50

171 of threatened or endangered species such as the Wood Stork. In addition, the large size and height of an upland CDF compared to the flat topography of the area would also have to considered, along with the concept of land disposal of sediment containing small quantities of residual pesticides and significant concentrations of P. Legal challenges may be significant and would likely focus on two areas, the first of which is the CDF location. This includes the general approach (e.g., in-lake versus upland) and the specific location (e.g., an upland facility to be constructed at a specific location). A dredging project may also face a legal challenge on the basis that the water quality improvements are inconsistent with the project costs (i.e., cost-benefit). Based on a combination of its high cost, limited improvements in water quality, and potential for litigation, this performance measure is given a score of PM 5D: No Impacts on Water Supply or Lake Operations The potential for impacts to water supplies is primarily associated with sediment resuspended during dredging. The concern is that under certain conditions, resuspended sediment may migrate into areas of the lake that are used for water supply purposes. Given the overall size of the lake and work conducted at other sites, this may not be a problem; however, the magnitude of potential consequences is significant enough that additional site-specific studies would be required to further assess this potential issue. These studies would likely include a larger scale dredging study (compared to the EA study; EA, 2002b) combined with additional hydrodynamic and sediment transport modeling for the lake. The case study literature reviewed in evaluating this performance measure included the results of a large-scale dredging study conducted by the USACE in Calumet Harbor (including the test of a hydraulic cutterhead dredge). The results of this study included calculating the size of the dredge plume (identified as the area with TSS concentrations 10 mg/l above background). For the cutterhead dredge, this area was only 0.5 ha (Hayes et al., 1988). For the purposes of this FS, we have assumed that migration of dredged resuspended sediment, especially during storms, could be high in Lake Okeechobee. Water supply intake structures (some located miles off-shore) could be vulnerable to increased TSS and sedimentation Given that dredging would occur over a period of 15 years and the 4/10/2003 engineers & scientists 5-51

172 frequent occurrence of storms in South Florida (sometimes daily in the wet season), dredging operations could be a nuisance to water plant operations. With regard to potential impacts to lake operations, there would be minor changes in the flood storage capacity of the lake associated with the construction of an in-lake or shoreline CDF. While these changes would be minor in nature, consideration would have to be given during preparation of the EIS as well as in the design and permitting processes relative to potential mitigative measures. Based on the above, this performance measure is given a score of 2. 4/10/2003 engineers & scientists 5-52

173 6. Summary and Recommendations 6.1 Project Summary This Evaluation of Alternatives report represents the cornerstone of the three-year Lake Okeechobee Sediment Management FS. The study, commissioned by the District in 2000, was designed to analyze possible approaches to reduce internal phosphorus loading in Lake Okeechobee and included both a comprehensive technical assessment and an extensive public and interagency outreach effort. The FS was designed to progress in five major stages or tasks: Task 1 Establishment of goals and performance measures (BBL, 2001a) and preparation of a public outreach plan (BBL, 2000); Task 2 Development of a specific array of alternatives to be evaluated in detail in the Feasibility Study (BBL, 2001b); Task 3 Preparation of a work plan for conducting the detailed evaluation of alternatives (BBL 2002); Task 4 Detailed evaluation of the alternatives (the focus of this document); and Task 5 Prioritization of alternatives, weighting of performance measures, and selection of an appropriate course of action. Tasks 1 through 3 are described in detail in the reports generated during each stage; the key results are summarized below. Public Outreach The primary component of the outreach effort was a series of four public meetings, but also included distribution of fact sheets to more than 800 interested individuals, development of a project website, establishment of a document repository, placement of meeting notices in local newspapers, and personal contact with key representatives of the public and government agencies. The public outreach effort was critical to the progress of the study, and yielded valuable input and insight that was considered and incorporated throughout the three-year process. 4/10/2003 engineers & scientists 6-1

174 Goals and Performance Measures The five main goals of the project developed during Task 1 with input from interested parties and the public are as follows: Goal 1 Maximize water quality improvements; Goal 2 Maximize engineering feasibility and implementability; Goal 3 Maximize cost effectiveness; Goal 4 Maximize environmental benefits; and Goal 5 Maximize socioeconomic benefits. Twenty six performance measures associated with the above-referenced goals, which were also developed collaboratively with the public and regulatory communities, are summarized in Section 2 and described in more detail in Appendix F. Development of Alternatives Following an initial screening of a wide range of available sediment management technologies and process options, 36 were deemed potentially applicable for managing internal phosphorus loading in Lake Okeechobee. These 36 options were evaluated in detail in with respect to potential feasibility for use in the lake. Fourteen technologies and process options were retained and used as building blocks to create a set of sediment management alternatives, that if implemented, could potentially meet the objective of reducing internal phosphorus loading. Work Plan In Task 3, the team developed the Work Plan for the Evaluation of Alternatives, a work breakdown structure in essence a detailed road map for coordinating and completing the evaluation of alternatives (BBL, 2002). The processes identified in Task 3 were applied in the formal evaluation presented in this report. 4/10/2003 engineers & scientists 6-2

175 Since the finalization of the Development of Alternatives report and the Work Plan, the alternatives that would be subjected to the detailed evaluation contained in this report were refined in an effort to strike a balance between the capability of the tools used in the analyses to differentiate among the alternatives. The final list of alternatives is as follows: No In-Lake Action with monitoring of external loads (see Section 3), Chemical Treatment with aluminum compounds (see Section 4), and Hydraulic Dredging with various post-dredge sediment management scenarios (see Section 5). These alternatives represent the possible range of options that could be implemented in the lake. It is important to recognize that although No In-Lake Action does not entail any active in-lake sediment management activities, it is decidedly not a do nothing approach. This alternative incorporates extensive lake and watershed monitoring efforts and aggressive watershed management practices to achieve restoration goals for Lake Okeechobee. 6.2 Results of the Evaluation of Alternatives This report is the culmination of the technical evaluation portion of the FS. It satisfies both the overall charge of the study and the regulatory requirements (described in Section 1.3), and provides the District with thorough, defensible quantitative and qualitative information that can be used to develop a plan for the future of Lake Okeechobee. The overall results of the alternative evaluation are summarized below, and scores, designed to provide a sense of each alternative s relative results with respect to each of the 26 performance measures developed in Task 1, are provided in Table ) No In-Lake Action assumes that the external loading rate of P will be reduced to a total load of 140 metric tons per year by 2015 in accordance with the TMDL established for the lake. For the purpose of modeling, external loads were converted to concentrations. The phosphorus concentration and external loading reduction schedule assumed in the modeling analysis (described in Section 3) consists of three parts: Baseline conditions start in 2000 with an initial load that reflects the average load for the previous 10 years. 4/10/2003 engineers & scientists 6-3

176 The external total phosphorus (TP) load is assumed to decline linearly by 25% between 2000 and This reduction is attributed to the implementation of best management practices (BMPs) in the watershed. Between 2010 and 2015, the external load is assumed to decline further to the TMDL goal, also as a result of watershed management. Modeling results for the No In-Lake Action scenario indicate a 25% decrease in the annual frequency of algal blooms (from a current annual likelihood of approximately 20%), to below a 15% annual probability of a bloom occurrence by 2015 and a decrease to below a 10% annual probability by Steady-state lake recovery conditions essentially would be achieved around 2063, approximately 35 years from the point that external loads are reduced to the inflow concentration of 40 µg/l (see Section 3). 2) Chemical Treatment, using alum and sodium aluminate, is estimated at a cost of approximately $493 million. Chemical treatment would start about year 2012 and would take 3 years to complete. Modeling results and technical evaluations indicate that chemical treatment would effectively inactivate the upper 10 centimeters of phosphorus in existing sediment and much of the new phosphorus introduced into the sediments, for about 15 years. With chemical treatment, the target of an annual likelihood of algal bloom occurrence of 10% (or less) in the near-shore, is achieved approximately 15 years earlier than predicted for the No In-Lake Action alternative. Chemical treatment also reduces the time to reach the in-lake TP goal compared to the No In- Lake Action alternative. Under the No In-Lake Action scenario, the ILPM and LOWQM models predict achievement of 90% of the 40 µg/l target (when compared to current concentrations), by approximately 2033 and 2042, respectively. If alum were applied to the lake according to the protocols of the chemical treatment alternative, both models predict that Lake Okeechobee would show improvements quite rapidly. Specifically, reductions in pelagic 4/10/2003 engineers & scientists 6-4

177 TP concentrations reach 90% of the predicted steady state recovery concentration by 2015, which is approximately 20 to 30 years earlier than the No In-Lake Action alternative. Beyond 15 years, the concurrent reductions in external loads are primarily responsible for improvements in water quality. If reductions in external loads are delayed or are not achieved, chemical treatments would have to be repeated about every 15 years to maintain the steady state recovery conditions (see Section 4). 3) Dredging, using hydraulic dredges, is estimated at a cost of approximately $3 billion. Dredging would start about 2015 and would take 15 years to complete. The technical evaluations and water quality modeling results indicate that dredging can never remove all the targeted sediment, and the layer left behind regardless of its thickness would continue to release phosphorus into the water column. Hence, this alternative shows limited or no effectiveness (Section 5). Figure 6-1 presents a graphic comparison of chemical treatment and dredging compared to the No In-Lake Action alternative. These plots show concentrations of TP for both chemical treatment and dredging normalized to the concentration of TP predicted for the No In-Lake Action alternative. Relative concentrations greater than 1 indicate that the alternative predicted higher lakewater TP concentrations than the No In-Lake Action alternative, while relative concentrations less than 1 indicate improved performance. The upper plot compares results using the ILPM, and the lower plot compares the results using the LOWQM. On the upper plot, two dredging recovery rates are shown. The 4.5% per year is the most realistic removal rate, as discussed in Section 5. While the 7.4% removal rate per year is provided here for comparison, it is unrealistic due to the first order decay method of analysis used and is an overestimate of the removal rate anticipated (Section 5). 4) The issue of residual sediment remaining after dredging was a key factor considered in the assessment of dredging effectiveness. A comprehensive evaluation, discussed in detail in Section 5, along with consideration of dredging case studies indicate that a layer of loose, 4/10/2003 engineers & scientists 6-5

178 unconsolidated sediment will remain after dredging that will continue to serve as a source of P to the water column. Even if an optimistic residual P concentration is assumed, after 2060 the performance of the dredging alternative is essentially equivalent to the No In-Lake Action alternative. It is possible that innovative approaches to addressing this residual sediment could improve dredging performance; however, at this time there is no straightforward solution. 5) Uncertainties related to the findings presented in this feasibility study are in large part associated with the expectation that the TMDL goal established for Lake Okeechobee by the FDEP can be achieved by All analyses are based on the assumption that external phosphorus loads will be reduced to the target TMDL of 140 metric tons to achieve an in-lake restoration target concentration of 40 µg/l by If achievement of the TMDL goal is delayed, the results predicted in the modeling analyses presented in this FS would be pushed back by an equivalent time period (i.e., if the TMDL target is not achieved until 2025, all timeframes discussed in items 1 through 3 above would be delayed by 10 years). The time period necessary for the lake to reach steady-state recovery (35 years) would remain the same, but obviously the year recovery is achieved is dependent on achievement and maintenance of the TMDL goal. Clearly, meeting the TMDL goal on time is critical to the future conditions in the lake; however, achievement of this goal is the key overarching uncertainty in this analysis. 6) Direct sediment re-suspension was found to be less important for internal phosphorus recycling than most have previously believed. Results of modeling conducted for this study and evaluation of long-term water quality data suggest that consolidated sediment resuspension may only contribute a minor fraction (17%) to the dynamics of water column total phosphorus in Lake Okeechobee, and that resuspension of algal cells and remains as they slowly settle from the water column may be more important by a factor of 5, or 83% (Section 3). 6.3 Recommendations 1) Consistent with current District policies and practice, the following activities should continue: a. Water quality monitoring should continue to verify that reductions in external loads resulting from activity in the watershed are proceeding as planned. 4/10/2003 engineers & scientists 6-6

179 b. Monitoring should include real time information for parameters such as total suspended solids, phosphorus, soluble reactive phosphorus, ph, chlorophyll a, temperature, and turbidity under a variety of weather conditions that can occur in Lake Okeechobee (e.g., storm events, high wind/wave conditions). 2) The District may wish to measure the actual depth of exchange of phosphorus in lake sediments. The actual depth of exchange of phosphorus from surficial sediments to the water column has not been directly measured in Lake Okeechobee sediments. The modeling performed for this feasibility study included 2-cm and 4-cm exchange depths for the LOWQM, and a 5-cm exchange depth for the ILPM. If measured exchange depths are indeed smaller, as is suspected, then the results of this feasibility study could be biased toward underpredicting the rate of lake recovery in response to reductions in external loads. 3) The District may wish to consider further exploring sediment burial rates in Lake Okeechobee. Improved estimates (i.e., greater spatial resolution) for sediment and P burial/deposition rates across the lake basin would serve to refine and improve model certainty. These are key attributes for accurate estimation of lake response to phosphorus load reduction, using existing models and modeling tools underdevelopment. 4) The District may wish to repeat modeling tasks using updated data sets at key junctures during the external load reduction schedule to confirm that conditions are proceeding as expected. 5) If it becomes a concern that external load reduction schedules may not be achieved as expected and water quality conditions are not improving as anticipated, chemical treatment using alum could be an effective interim option. Before chemical treatment could be permitted and/or implemented, a full-scale pilot test would be required. 4/10/2003 engineers & scientists 6-7

180 Table 6-1 Summary of Performance Measure Scores for No In-Lake Action, Chemical Treatment, and Dredging Alternatives Performance Measure Scoring Criteria No In- Lake Action Chemical Treatment Dredging 1A Minimize time to achieve phosphorus target 1B Maximize reductions in watercolumn phosphorus concentrations 1C Maximize TSS reductions in the short term and the long term 1D Minimize algal blooms 1E Minimize exceedances of waterquality standards in the short term and the long term GOAL 1: Maximize water quality improvements Higher scores mean a more rapid rate of recovery. Higher scores mean average total phosphorus concentration at or near 40 µg/l Higher scores mean greater TSS reductions and an increase in the maximum water depth able to support submerged aquatic vegetation in the near-shore zone (i.e., improved light transparency). Higher scores mean lower incidence of blooms and reduced likelihood of cyanobacterial dominance of phytoplankton community. Two scores were given one each for shortand long-term effects; higher scores mean fewer predicted exceedances. 3/4 4/4 2/ /4 3/4 3/4 1F Minimize downstream impacts Higher scores mean net positive impacts /2 2A Maximize technical reliability 2B Maximize technical scaleability 2C Maximize equipment and material availability 2D Maximize performance GOAL 2: Maximize engineering feasibility and implementability Technologies with higher scores are indicative of greater reliability. Higher scores indicate that the approach is more likely to be scalable to meet the needs of this project. Scores were assigned from 1 to 5, based on relative and predicted ability to implement (i.e., supply) construction of an alternative. A higher score (i.e., 5) would imply that sufficient equipment and materials are locally and readily available. Permanence was rated using a relative scale of 1 to 5 (i.e., 5 for highest degree of permanence) based on qualitative and quantitative estimates of performance Notes: Where two scores are present, the first score is for short term and the second score is for long term. Numbers in bold represent the highest score given for a particular performance measure. 4/10/2003 engineers & scientists 6-8

181 Table 6-1 (cont.) Summary of Performance Measure Scores for No In-Lake Action, Chemical Treatment, and Dredging Alternatives Performance Measure Scoring Criteria No In- Lake Action Chemical Treatment Dredging 2E Minimize on-shore land-use needs and conflicts 2F Satisfy permitting requirements 3A Minimize construction costs 3B Minimize O&M costs 3C Maximize benefits (material reuse) 4A Maximize benefits to wetland vegetation in littoral zone 4B Maximize benefits to SAV Relative scores were assigned from 1 to 5, based on estimated amount of on-shore land required, duration, and potential conflicts with public projects (lower scores for alternatives with greater land use and potential conflict; higher scores for alternatives with minimal land use and lesser potential conflict). Alternative evaluation scores will range from 5 (high permitting probability) to 1 (low permitting probability. GOAL 3: Maximize cost effectiveness Using the range of costs developed for the alternatives, scores were assigned from 1 to 5, based on a relative order of magnitude (1 for the highest cost alternatives and 5 for the lowest cost alternatives). Cost values are also directly reported. Using the range of costs developed for the alternatives, relative scores were assigned from 1 to 5, based on order of magnitude estimates (1 for the highest cost alternatives and 5 for the lowest cost alternatives). Using the range of costs developed for the alternatives and the potential revenue generated by the material reuse subalternative, relative scores were assigned from 1 to 5, based on order of magnitude estimates (5 for the highest benefits and 1 for the lowest benefits). GOAL 4: Maximize environmental benefits Higher scores mean greater decrease in phosphorus and likely improvement in plant community structure. Higher scores mean a low probability of short-term impacts and high potential for improved conditions in the long term NA NA Notes: Where two scores are present, the first score is for short term and the second score is for long term. Numbers in bold represent the highest score given for a particular performance measure. 4/10/2003 engineers & scientists 6-9

182 Table 6-1 (cont.) Summary of Performance Measure Scores for No In-Lake Action, Chemical Treatment, and Dredging Alternatives Performance Measure Scoring Criteria No In- Lake Action Chemical Treatment Dredging 4C Maximize benefits to fish and aquatic invertebrate communities 4D Minimize negative impacts to the manatee 4E Minimize negative impacts to the alligator 4F Minimize negative impacts to the Okeechobee Gourd 4G Minimize negative impacts to the snail kite and wading birds 5A Maximize regional socioeconomic benefits 5B Minimize environmental/ social inequities 5C Maximize community acceptance 5D No impacts on water supply or lake operations Higher scores mean high probability for enhancement of habitat quality and community composition and structure. 3/4 3/3 2/3 Higher scores mean high probability for positive impacts on the habitat and forage requirements. Higher scores mean high probability for enhancement of suitable habitat Higher scores (up to 5) mean an increase in suitable habitat is likely; alternatives that require actions in near-shore areas, Kreamer, Torry, or Ritta islands, or near the rim canal would be given a low score (1). Higher scores mean a high probability of positive effects on critical habitat/forage GOAL 4: Maximize environmental benefits Relative scores were assigned from 1 to 5 (5 assigned to alternatives with the greatest beneficial impact, 1 assigned to alternatives with the greatest negative impact). A 5 (high score) was assigned to the alternatives with the most even allocation of impact, and a 1 was assigned to the alternatives that result in the most lopsided allocation of impact. Higher scores mean greater degree of apparent community acceptance and lower probability of legal challenge. Scores assigned on a relative basis, with 5 assigned to alternatives that do not have any impact and 1 assigned to those with significant adverse impacts Notes: Where two scores are present, the first score is for short term and the second score is for long term. Numbers in bold represent the highest score given for a particular performance measure. 4/10/2003 engineers & scientists 6-10

183 7. References Aumen, N. and S. Gray Research Synthesis and Management Recommendations from a Five- Year, Ecosystem-Level Study of Lake Okeechobee, Florida. Archiv fur Hydrobiologie, Advances in Limnology45: DOR #173 (B). BBL Public and Interagency Public Outreach Plan. BBL. 2001a. Goals and Performance Measures for the Lake Okeechobee Sediment Management Feasibility Study (Boca Raton, FL: June 2001). BBL. 2001b. Development of Alternatives for the Lake Okeechobee Sediment Management Feasibility Study (Boca Raton, FL: October 2001). BBL Work Plan for the Evaluation of Alternatives Lake Okeechobee Sediment Management Feasibility Study (C-11650). South Florida Water Management District, West Palm Beach, Florida, May Best, G. R Natural wetlands southern environment: Wastewater to wetlands, where do we go from here? In K.R. Reddy and W.H. Smith [eds.], Aquatic Plants for Water Treatment. Magnolia Publishing Inc., Orlando, FL: Bierman, Jr., V. R. and R. T. James A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Diagnostic and sensitivity analyses. Water Res. 29: Brenner M., and M.W. Binford Relationships between concentrations of sedimentary variables and trophic state in Florida lakes. Canadian Journal of Fisheries and Aquatic Sciences 45: Boudreau, B. P Mean mixed depth in sediments: The wherefore and why. Limnol. Oceanogr. 43: Brezonik, P. L. and D. R. Engstrom Modern and Historic Accumulation Rates of Phosphorus in Lake Okeechobee, Florida. Journal of Paleonlimnology 20: 31-46, Brezonik, P. L. and D. R. Engstrom Modern and historic accumulation rates of phosphorus in Lake Okeechobee, Florida. Journal of Paleolimnology 20: Carrick, H. J., F. J. Aldridge, and C. L. Schelske Wind influences phytoplankton biomass and composition in a shallow, productive lake. Limnol. Oceanogr. 38: Cooke, G. D., E. B. Welch, S. A. Peterson, and P. R. Newroth Restoration and Management of Lakes and Reservoirs. Boca Raton, Florida: CRC Press LLC. Cooke, G. D., E. B. Welch, C. Lind, and T Eberhardt Phosphorus Inactivation in Stratified/Unstratified Lakes and Inflow Interception. Workshop #1 at 22nd Annual International Symposium North American Lake Management Society, Anchorage, Alaska. October 29, /10/2003 engineers & scientists 7-1

184 EA Engineering, Science, & Technology, Inc. (EA). 2002a. Lake Okeechobee Pilot Dredging Project. Draft Sediment Bench-scale Testing Report. EA Engineering, Science, & Technology, Inc. March EA. 2002b. Lake Okeechobee Pilot Dredging Project Report. EA Engineering, Science, & Technology, Inc. June Engstrom, D. R. and P. L. Brezonik Lake Okeechobee Phosphorus Dynamics Study, Vol. V. Historical Phosphorus Accumulation Rates. Final Report Contract C Report to South Florida Water Management District. Fisher, M. M., K. R. Reddy, and R. T. James Long-term changes in the sediment chemistry of a large shallow subtropical lake. Lake and Reservoir Management (accepted). Fisher, M. M., K. R. Reddy, and R. T. James. In review. Internal Nutrient Loads from Sediments in a Shallow, Subtropical Lake. Hamrick, J. H. and T. S. Wu Computational design and optimization of the EFDC/HEM3D surface water hydrodynamic and eutrophication models. In G. Delic and M. F. Wheeler [eds.], Next Generation Environmental Models and Computational Methods. Society for Industrial and Applied Mathematics (SIAM), Philadelphia. Foster Wheeler Final Pre-Design Field Test Dredge Technology Evaluation Report, New Bedford Harbor Superfund Site, New Bedford, Massachusetts. Gensemer, R.W. and R.C. Playle Aluminum toxicity, speciation, and bioavailability in aquatic environments. CRC Critical Reviews in Environmental Science and Technology 29(4): Gibbons, M. V., F. D. Woodwick, W. H. Funk, and H. L. Gibbons Effects of a multiphase restoration, particularly aluminum sulfate application, on the zooplankton community of a eutrophic lake in eastern Washington. J. Freshwater Ecology 2: Harvey, R. and K. E. Havens Lake Okeechobee Issue Team Action Plan. Report to the South Florida Ecosystem Restoration Working Group. Havens, K. E. and C. L. Schelske The importance of considering biological processes when setting total maximum daily loads (TMDL) for phosphorus in shallow lakes and reservoirs. Environmental Pollution, in press. Havens, K. E. and W. W. Walker, Jr Development of a total phosphorus concentration goal in the TMDL process for Lake Okeechobee, Florida (USA). Lake and Reservoir Management 18: Havens, K. E., N. G. Aumen, R. T. James, and V. H. Smith Rapid ecological changes in a large subtropical lake undergoing cultural eutrophication. Ambio 25: /10/2003 engineers & scientists 7-2

185 Havens, K.E., B. Sharfstein, M.A. Brady, T.L. East, M.C. Harwell, R.P. Maki, and A.J. Rodusky. In preparation. Stress and recovery of submerged aquatic vegetation in a large subtropical lake in Florida, USA. Havens, K. E., D. Gawlik, P. Gray, and G. Warren Working Hypotheses: Lake Okeechobee Conceptual Model. November 1, Hayes, D. F., T. J. Olin, J. C. Fischenich, and M. R. Palermo Wetlands Engineering Handbook. ERDC/EL TR-WRP-RE-21. U.S. Army Engineer Research and Development Center, Vicksburg, MS (March 2000). Hayes, D. F., T. N. McLellan, and C. L. Truitt Demonstrations of Innovative and Conventional Dredging Equipment at Calumet Harbor, Illinois. Miscellaneous Paper EL US Army Engineer Waterways Experiment Station, Vicksburg (February 1988). Hwang, K.N. and A.J. Mehta Fine Sediment Erodibility in Lake Okeechobee, Florida. Report to South Florida Water Management District. November, James, R. T. and V. R. Bierman, Jr A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Model calibration. Water Res. 29: James, R. T., J. Martin, T. Wool, and P. F. Wang A sediment resuspension and water quality model for Lake Okeechobee. Journal of the American Water Resources Association 33: James, R. T., M. J. Erickson, V. R. Bierman, and S. Hinz. In preparation. Predicted Water Quality Changes in Lake Okeechobee due to Reservoir-Assisted Stormwater Treatment Areas (RaSTAs). Unpublished draft manuscript. South Florida Water Management District, West Palm Beach, FL. Janus et al., 1990 Jensen, J.S., P. Kristensen, E. Jeppesen, and A. Skytthe Iron:phosphorus ratio in surface sediment as an indicator of phosphorus release from aerobic sediments in shallow lakes. Hydrobiologia 235/236: Jin, K. R., and J. H. Hamrick Application of a three-dimensional model hydrodynamic model for Lake Okeechobee. Jour. Hydraul. Eng. 126: Jin, K. R., R. James, W. Lung, D. Loucks, R. Park, and T. Tisdale Assessing Lake Okeechobee eutrophication with water-quality models. Journal of Water Resources Planning Management January/February 1998: Kirby, R. R., C. H. Hobbs, and A. J. Mehta Fine Sediment Regime of Lake Okeechobee, Florida. UFL/COEL-89/009. University of Florida, Coastal & Oceanographic Engineering Department: Gainesville, Florida (November, 1989). 4/10/2003 engineers & scientists 7-3

186 Kleeberg, A. and J. G. Kohl Assessment of the long-term effectiveness of sediment dredging to reduce benthic phosphorus release in shallow Lake Muggelsee (Germany). Hydrobiologia 394: Lampert, W. and U. Sommer Limnoecology: The ecology of lakes and streams. New York, New York: Oxford University Press. Maceina, M. J. and D. M. Soballe Wind-related limnological variation in Lake Okeechobee, Florida. Journal of Lake and Reservoir Management 6(1): Moore, P. A., D. R. Reddy, and M. M. Fisher Phosphorus flux between sediment and overlying water in Lake O, Florida: spatial and temporal variations. J. Enviro. Qual., 27: Moss, B., J. Madgwick, and G. Phillips A Guide to the Restoration of Nutrient-Enriched Shallow Lakes. Environment Agency, Broads Authority, UK. Murakami, K Dredging for controlling eutrophication of Lake Kasumigaura Japan. Lake and Reservoir Management. Proc. 3 rd Annual Conf., North America Lake Management Soc., Knoxville, TN: [from Pollman et al., 1988] NRPA Protecting the Marine Environment Since A Market for Dredge Mud? Yes. (December 28, 1999) OA Systems, Corporation (OA) Conceptual and Feasible Uses of Dredged Material: Consulting Assistance for the Lake Okeechobee Sediment Removal Feasibility Study and Pilot Dredging Project. Draft December 3, Palermo, M. R. and D. E. Averett Confined Disposal Facility (CDF) Containment Measures: A Summary of Field Experience. DOER Technical Notes Collection. ERDC TN-DOER-C18. U.S. Army Engineer Research and Development Center, Vicksburg, MS. Pfeuffer, R Pesticide Residue Monitoring in Sediment and Surface Water Bodies within the SFWMD, Nol. II. DRE-293. Technical Publication Pfeuffer, R. J. and F. Matson Pesticide Surface Water and Sediment Quality Report - May 2000 Sampling Event. South Florida Water Management District. Pollman, C. D Development of a Phosphorus Diagenetic Model for Lake Okeechobee Sediments. Final Report submitted to South Florida Water Management District. KBN Engineering & Applied Sciences, Inc, Gainesville, FL. Pollman, C. D Overview of a Simple Approach to Modeling Internal Loading in Lake Okeechobee. Draft Report to Florida Department of Environmental Protection, Tallahassee, Florida. Tetra Tech, Gainesville, Florida. Pollman, C. D. No date. Development of a diagenetic model for Lake Okeechobee sediments. Unpublished manuscript. 4/10/2003 engineers & scientists 7-4

187 Reddy, K. R. 1991a. Lake Okeechobee phosphorus dynamics study, Vol. II. Physico-chemical properties of sediments; Final Report Contract C Report to South Florida Water Management District. Reddy, K. R. 1991b. Lake Okeechobee phosphorus dynamics study, Vol. III. Biogeochemical processes in the sediments; Final Report Contract C Report to South Florida Water Management District. Reddy, K. R., M. M. Fisher, J. R. White, and W. G. Harris Potential Impacts of Sediment Dredging on Internal Phosphorus Load in Lake Okeechobee. Draft Report to South Florida Water Management District. Reddy, K. R., J. R. White, M. M. Fisher, H. Pant, Y. Wang, K. Grace, and W. G. Harris Potential Impacts of Sediment Dredging on Internal Phosphorus Load in Lake Okeechobee. Final Report to South Florida Water Management District. July, Rigler, F. H Appendix: Phosphorus Cycling in Lakes. In F. Ruttner, Fundamentals of Limnology. Toronto: University of Toronto Press. Roukema, D. C., J. Driebergen, and A. G. Fase Realisation of the Ketelmeer storage depot. Terra Et Aqua (71), IADC, The Netherlands. Rydin, E. and E. B. Welch Aluminum dose required to inactivate phosphate in lake sediments. Water Research. 32: Rydin, E. and E. B. Welch Dosing alum to Wisconsin lake sediments based on in vitro formation of aluminum-bound phosphate. Lake and Reservoir Management 15: Rydin, E., B. Huser, and E. B. Welch Amount of phosphorus inactivated by alum treatments in Washington lakes. Limnol. Oceanogr. 45: SAS Institute, Inc. (SAS) JMP Statistics and Graphics Guide, Version 3. SAS Institute Inc., Cary, NC. South Florida Water Management District (SFWMD) Surface water improvement and management (SWIM) plan update for Lake Okeechobee. South Florida Water Management District, West Palm Beach, Florida. SFWMD. 2000a. Lower West Coast Regional Water Supply Plan. Water Supply Planning and Development Department. South Florida Water Management District, West Palm Beach, Florida. April SFWMD. 2000b. Lower East Coast Water Supply Plan. Water Supply Planning and Development Department. South Florida Water Management District, West Palm Beach, Florida. May SFWMD In-Lake Projects, Submerged Aquatic Vegetation Assessment. 4/10/2003 engineers & scientists 7-5

188 Steinman, A. D., K. E. Havens, N. G. Aumen, R. T. James, K. R. Jin, J. Zhang, B. H. Rosen Phosphorus in Lake Okeechobee: Sources, Sinks, and Strategies (pp ) in the book Phosphorus Biogeochemistry in Subtropical Ecosystems. Eds. K. R. Reddy, G. A. O Connor, and C. L. Schelske. Lewis Publishers: Boca Raton, FL. Stumm, W. and J. J. Morgan Aquatic chemistry. New York, New York: Wiley-Intersciences. United States Army Corps of Engineers (USACE) Dredging and Dredged Material Disposal, Engineer Manual. EM Department of the Army Corps of Engineers Office of the Chief of Engineers (March 1983). USACE Confined Disposal of Dredged Material. Engineer Manual Washington, D.C. September USACE Dredging: Building and Maintaining Our Underwater Highways. Miscellaneous brochure, Washington, DC. USACE. 1999a. Comprehensive Everglades Restoration Program in Central and Southern Florida Comprehensive Review Study. South Florida Water Management District, West Palm Beach, Florida (April 1999). USACE. 1999b. Draft Integrated Feasibility Report and Environmental Impact Statement for Lake Okeechobee Regulation Schedule Study. Jacksonville District, FL (June 1999). United States Environmental Protection Agency (USEPA) Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA. Interim Final. EPA/540/G-89/004. (Washington, DC: October 1988). USEPA Revisions to OMB Circular A-94 on Guidelines and Discount Rates for Benefit-Cost Analysis. OSWER Directive No See also subsequent annual revisions to OMB Circular A-94. USEPA Assessment and Remediation of Contaminated Sediments (ARCS) Program Remediation Guidance Document. EPA 905/R Great Lakes National Program Office, Chicago, IL (October 1994). USEPA Assessment and Remediation of Contaminated Sediments (ARCS) Program Guidance for In-Situ Subaqueous Capping of Contaminated Sediments. USEPA, A Guide to Developing and Documenting Cost Estimates During the Feasibility Study. EPA 540-R OSWER (July 2000). United States Fish and Wildlife Service (USFWS) South Florida Multi-Species Recovery Plan. USFWS, Southeast Region, Atlanta, Georgia. 4/10/2003 engineers & scientists 7-6

189 Van der Does, J., P. Verstraelen, P. Boers, J. Van Roestel, R. Roijackers, and G. Moser Lake restoration with and without dredging of phosphorus-enriched upper sediment layers. Hydrobiologia 233, Van Hullebusch, E., V. Deluchat, P. M. Chazal, and M. Baudu Environmental impact of two successive chemical treatments in a small shallow eutrophied lake: Part I Case of aluminum sulphate. Environmental Pollution 120: Walker, Jr., W.W Revised TMDL calculations refinements to steady-state model. Technical document prepared for Lake Okeechobee TMDL Technical Advisory Committee. Florida Department of Environmental Protection, Tallahassee, Florida. Welch, E. B. and G. D. Cooke Effectiveness and longevity of alum treatments in lakes. Lake and Reservoir Management 15: Wetzel, R Limnology. Philadelphia, Pennsylvania: WB Saunders. Winchester, B. H. and J. C. Higman Nutrient removal by a Florida hardwood swamp receiving secondarily treated effluent, pp In K. R. Reddy and W. H. Smith [eds.], Aquatic Plants for Water Treatment. Magnolia Publishing Inc., Orlando, FL. 4/10/2003 engineers & scientists 7-7

190 Additional Sources and Resources Community Outreach Meeting Minutes - Public/Interagency Meeting #1 January 10, 2002 Meeting Minutes - Public/Interagency Meeting #2 July 19, 2001 Meeting Minutes - Public/Interagency Meeting #3 April 4, 2002 Newspapers Palm Beach Post Palm Beach County, FL Glades County Democrat Moore Haven, FL The Sun Pahokee and Belle Glade, FL Clewiston News - Clewiston Okeechobee News- Okeechobee, FL Agency Contacts Environmental and Land Use Law Center Blackwelder, Brion 3305 College Avenue, Ft. Lauderdale, Florida Florida Department of Environmental Protection (FDEP) Zebuth, Herb. Environmental Manager for the Southeast District P.O. Box 15425, West Palm Beach, Florida Florida Fish & Wildlife Conservation Commission (FWC) Warren, Gary. Biological Scientist IV 7922 N.W. 71 st Street, Gainesville, Florida Walsh, Joe. Bio-Administrator II th Avenue, Vero Beach, Florida Florida Sportsmen Conservation Association Maharrey, Byron 329 Emerson Circle, Palm Springs, Florida Friends of Lake Okeechobee Head, Carol 2252 S.W. 22 nd Circle, Okeechobee, FL /10/2003 engineers & scientists 7-8

191 St. Lucie River Initiative Quakenbos, Max N.W. Palmetto Terrace, Stuart, Florida U.S. Army Corps of Engineers (USACE) Hess, John C. Chief of the Environmental & HTRW Section of the Jacksonville, District, P.O. Box 4970, Jacksonville, Florida Hopple, Clyde. Civil Engineer 400 W. Bay Street, Jacksonville, Florida Thompson, Curt. Restoration & Planner and Outreach Specialist 3301 Gun Club Road, West Palm Beach, Florida U.S. Environmental Protection Agency (USEPA) Hughes, Eric. Ecosystem Restoration Section P.O. Box 4970, Jacksonville, Florida Socio-Economic Sources/Resources Background Data Central and Southern Florida Project Comprehensive Review Study; Appendix E. Socio-Economics; US Army Corps of Engineers/South Florida Water Management District; April (H) Population Data Claritas, Inc.; 53 Brown Road; Ithaca, NY; CONNECT service - which provides access to most of the necessary population and economic data for the most recent year by a variety of screens, e.g., zip code, business type, radius around a point, etc. The Internet address is: (A user ID is needed to access the data files.) (H) Economic Data Claritas, (see above) The Bureau of Economic and Business Research; College of Business Administration; 221 Matherly Hall; P.O. Box ; Gainesville, FL; Internet address is: (H) 4/10/2003 engineers & scientists 7-9

192 Future Economic (Workforce Pattern) Data Agency for Workforce Innovation, Labor Market Statistics, The Atkins Building, Suite 300; 1320 Executive Center Drive, Tallahassee, FL ; Both BEBR and the AWI are the repositories for state data in their respective areas of interest. Hazen & Sawyer, P.C Natural Resource Analysis of Lake Okeechobee Phosphorus Management Strategies; Progress Report #2. October Hazen & Sawyer, P.C Natural Resource Analysis of Lake Okeechobee Phosphorus Management Strategies; Progress Report #3. February /10/2003 engineers & scientists 7-10

193 Modeling Data Files Primary data files to be used in LOWQM and MINEQL+ modeling, and analysis of TSS effects on SAV in the nearshore zone. File Name Source Date Description Lakeraw.2.xls Tom James 3/11/2002 Major ion chemistry, nutrient and TSS data for 154 stations, with data beginning as early as 1972 and ending as late as Chara.xls Tom James 2/14/2002 SAV Survey Data - Summary (April 1999 to August 2000). Includes plant standing crop data, TSS, DOC, chlorophyll a and optical data. Val.light.growth.xls Tom James 2/14/2002 Growth rate and PAR data analyzed. PAR+Growthrateper day,xls Tom James 2/14/2002 Appears to be same file as Val.light.growth.xls Porewater.1998.xls Tom James 2/14/2002 Porewater equilibrator chemistry data from Reddy (1991 a and b) sampled at 1 cm intervals. Parameters include NH 4 + -N, DRP, SO 4 2-, ph, CO 2, CH 4, and DIC. Two stations sampled, with several replicates. Ca.budget.year.xls Tom James 3/11/2002 Ca budget analysis prepared by T. James for 1973 through C.lbudget.year.xls Tom James 3/11/2002 Cl budget analysis prepared by T. James for 1973 through Mg.budget.year.xls Tom James 3/11/2002 Mg budget analysis prepared by T. James for 1973 through Ionratios.xls Tom James 3/12/2002 Comparison of annual pelagic zone concentrations of TP and Ca with Mg and Cl concentrations. Sediments.1998.xls Tom James 3/12/2002 Appears to be a LOHTM model output file for a 1998 model run. Tpyearbud.xls Tom James 3/12/2002 TP budget analysis prepared by T. James for 1973 through Full SAV dataset.xls OK_LOI,.xls OKDates.xls OK-P-SUM.xls Karl Havens Dan Engstrom Dan Engstrom Dan Engstrom 3/12/2002 Full SAV dataset from 42 station program, April 1999 to October /15/2001 % organic carbon and % carbonate carbon concentrations (expressed as CaCO3) as determined from loss on ignition for each core as a function of depth. 11/29/2000 Dates and sediment mass accumulation rates by vertical horizon for stations M4, L3, M11, P10, N10, N12, L9, K8, N6, O8, M8, M18, and K18. 10/20/2000 Sediment P fractionation and accumulation rates for different intervals for 13 stations LOWQM files Tom James 2/05/ files, including 28 year data input file (okrecal.inp dated 10/25/2001) to run recalibrated LOWQM (lowqm3.0.for dated 1/11/2001; James et al., in preparation). In addition, a suite of model code, input, and output files (559 files) were obtained from Kang-Ren Jin on 3/12/2002. These files included SWAN output to be used as the wind-wave characteristics driver for LOHTM. 4/10/2003 engineers & scientists 7-11

194 Cost Evaluations Means, Heavy Construction Cost Data; Environmental Remediation Cost Data Unit Price. RS Means Company, Inc. (S) Metcalf & Eddy, Inc Wastewater Engineering Treatment, Disposal, and Reuse. New York, NY: McGraw-Hill, Inc. (S) United States Army Corps of Engineers (USACE) Dredging and Dredged Material Disposal, Engineer Manual. EM Department of the Army Corps of Engineers Office of the Chief of Engineers (March 1983). (S) USACE Confined Disposal of Dredged Material. Engineer Manual Washington, D.C. September (S) USEPA Assessment and Remediation of Contaminated Sediments (ARCS) Program Remediation Guidance Document. EPA 905/R Great Lakes National Program Office, Chicago, IL (October 1994). (S) United States, Office of Management and Budget. Pesticide Pfeuffer, Richard J. 3/89. Lake Okeechobee Pesticide Monitoring Report, SFWMD DRE-269, Technical Memorandum. Pfeuffer, Richard Herbicide Monitoring Program for N-Methylformamide and Fluridone in Lake Kissimmee. SFWMD. (compared to Lake O). Pfeuffer, Richard Pesticide Residue Monitoring in Sediment and Surface Water Bodies within the SFWMD, Nol. II. DRE-293. Technical Publication Pfeuffer, Richard J. and Francine Matson Pesticide Surface Water and Sediment Quality Report - May 2000 Sampling Event. South Florida Water Management District. SFWMD. January Pesticide Residue Monitoring in Sediment and Surface Water Within the South Florida Water Management District, Volume 2, Technical Publication #91-01, DRE-293. Additional Sources and Resources Andres, T.C. and G.P. Nabhan Taxonomic rank and rarity of Cucurbita okeechobeensis. FAO/IBPGR Plant Genetic Resources Newsletter 75/75: /10/2003 engineers & scientists 7-12

195 Avery, G.N. and L.L. Loope Endemic taxa in the flora of south Florida. Report T-558, U.S. National Park Service, South Florida Research Center, Everglades National Park, Homestead, FL. 39 pp. Bailey, L.H Three discussions in Cucurbitaceae. Gentes Herbarum 2: Bailey, L.H Species of Cucurbita. Gentes Herbarum 6: Bemis, W.P., A.M. Rhodes, T.W. Whitaker, and S.G. Carmer Numerical taxonomy applied to Cucurbita relationships. Amer. J. Bot. 57: Blake, N.M Land into water--water into land. Univ. Presses of FL, Tallahassee. viii pp. Decker, D.S. and L.A. Newsom Numerical analysis of archaeological Cucurbita pepo seeds from Hontoon Island, Florida. J. Ethnobiol. 8: Esquinas-Alcazar, J.T. and P.J. Gulick Genetic resources of Cucurbitaceae: a global report. International Board Plant Genetic Res., Rome. 101 pp. Filov, A.I Ekologija i klassifikatzija tkuy [Ecology and taxonomy of pumpkins]. Bjull. Glaun. Botan. Sad. (Moscow)[Bulletin of the Main Botanical Gardens]. 63: Hanna, A.J. and K.A. Hanna Lake Okeechobee: Wellspring of the Everglades. Bobbs-Merril Co., Indianapolis. 380 pp. Harper, F. (ed.) The Travels of William Bartram: Naturalist's Edition. Yale University Press, New Haven. xxxv pp. Harshberger, J.W The vegetation of south Florida, south of 27ø30' north, exclusive of the Florida Keys. Transactions, Wagner Free Institute of Science, Philadelphia. Howe, W.L. and A.M. Rhodes Host relationships of the squash vine Melittia cucurbitae with species of Cucurbita. Ann. Entom. Soc. Amer. 66: Johnson, L Beyond the fourth generation. Univ. Presses of FL, Gainesville. 230 pp. Merrill, E.D In defense of the validity of William Bartram's binomials. Bartonia 23:25. Nabhan, G.P Lost gourds and spent soils on the shores of Okeechobee. in Enduring Seeds. North Point Press, Berkeley. Robinson, R.W. and J.T. Puchalski Synonomy of Cucurbita martinezii and C. okeechobeensis. Cucurbit Genetics Coop. Rpt. 3: Small, J.K Narrative of a cruise to Lake Okeechobee. Amer. Museum J. 18: Small, J.K Wild pumpkins. J. New York Bot. Garden 23: Small, J.K The Okeechobee gourd. J. New York Bot. Gard. 31:10-4/10/2003 engineers & scientists 7-13

196 Tatje, B.E Status report on Cucurbita okeechobeensis. U.S. Fish and Wildlife Service, Jacksonville, FL. Walters, T.W. and D. Decker-Walters The elusive, endangered, and endemic Okeechobee gourd: the systematics of Cucurbita okeechobeensis (Cucurbitaceae). Final report submitted to Center for Plant Conservation, St. Louis, and U.S. Fish and Wildlife Service, Jacksonville, FL. 54 pp. Walters, T.W. and D. Decker-Walters Systematics of the endangered Okeechobee Gourd (Cucurbita okeechobeensis: (Cucurbitaceae). Systematic Botany 18(2): Will, L.E A cracker history of Okeechobee. Great Outdoors Assn., St. Petersburg, FL. 165 pp. For more information please contact: U.S. Fish and Wildlife Service 6620 Southpoint Drive South, Suite 310 Jacksonville, Florida /10/2003 engineers & scientists 7-14

197 LOADINGIN TRANSPORT OUT EVALUATION OFALTERNATIVES NOTE: WCA-WATER CONSERVATIONAREA LAKEOKEECHOBEE SEDIMENTMANAGEMENTFEASIBILITYSTUDY LAKEOKEECHOBEEAND SURROUNDINGAREAS 02/03 SYR-12 MFE /Fig 1-1.cdr ADAPTED FROM: SFWMD,1997B FORSFWMD FIGURE 1-1

198 OKEECHOBEE KISSIMMEERIVER 7-12 DEEP 7-12 DEEP 1-6 DEEP DEEP WEST PALM BEACH CANAL 7-12 DEEP 1-6 DEEP CALOOSAHATCHEE RIVER 1-6 DEEP NAUTICALMILES STATUTE MILES N. NEWRIVER CANAL HILLSBORO CANAL EVALUATION OFALTERNATIVES LAKEOKEECHOBEE SEDIMENTMANAGEMENTFEASIBILITYSTUDY INSETNOTTOSCALE LAKEOKEECHOBEESITEMAP 02/03 SYR-12 MFE /Fig 1-2.cdr ADAPTED FROM: INTERNATIONALSAILING SUPPLY,1995 FORSFWMD FIGURE 1-2

199 Total phosphorus content inmg/kgor partsper million of Lake Okeechobee surficial (0-10cm) sediments. EVALUATION OFALTERNATIVES LAKEOKEECHOBEE SEDIMENTMANAGEMENTFEASIBILITYSTUDY TOTALPHOSPHORUS CONTENT IN SURFICIALSEDIMENTS /03 SYR-12 MFE /Fig 1-3.cdr SOURCE: FISHER ETAL., FORSFWMD FIGURE 1-3

200 Habitat Regions SOURCE: SFWMD, 1997A. Pelagic Region (no plants) Littoral Region (emergent, submerged, and floating plants) Near-Shore Region (submerged plant beds, Chara, bulrush) ROCK ROCK 1998 Spatial Distribution of Sediment Types ADAPTED FROM: FISHER ET AL., 2001 SAND MUD LITTORAL PEAT ROCK DRAWINGS ARE NOT TO SCALE EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY HABITAT REGIONS & SPATIAL DISTRIBUTION OF SEDIMENT TYPES 02/03 SYR-12 MFE /Fig 1-4.cdr FOR SFWMD FIGURE 1-4

201 Phosphorus Concentration (mg/kg) Sediment Depth (cm) Legend Minimum Maximum 02/03 SYR-D12-DJH /Fig2-1.CDR Average Note: Average phosphorus concentrations were calculated by averaging phosphorus data for 11 sediment cores collected June 1988 and June 1989 as presented in Engstrom and Brezonik, EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY PHOSPHORUS CONCENTRATION BY DEPTH IN LAKE OKEECHOBEE MUD LAYER FIGURE FOR SFWMD 2-1

202 Wind Wind-induced waves Orbital velocity Sediment resuspension Particle-aqueous phase PO 4 3- exchange Dissolved PO 4 3- Algal uptake Shearing Stress BenthicCommunity Diffusion, Bioturbation Deposition Particulate Inorganic P Dissolved PO 4 3- Organic P 02/03 SYR-12 MFE /Fig2-2.cdr SOURCE: POLLMAN,2000. EVALUATIONOFALTERNATIVES LAKEOKEECHOBEE SEDIMENTMANAGEMENTFEASIBILITYSTUDY SIMPLIFIEDDIAGRAMILLUSTRATING MAJORPROCESSESANDTRANSPORT PATHWAYSINVOLVEDININTERNALLOADING OFPHOSPHORUS INSHALLOWLAKES FORSFWMD FIGURE 2-2

203 600 Total Load (tonnes) Varying Annual Inflow Constant (long-term average) Inflow Simulation Year External P loading schedule for Lake Okeechobee for the No-Action Alternative. Red line shows expected loading schedule if fractional reductions in surface water inputs shown in Table 3-2 are implemented and applied to long-term average inflow rates to the lake. Red line shows the actual load reductions implemented during the first 28 year cycle of the model simulations (both the ILPM and LOWQM use a 28-year looped annual hydrologic cycle based on observed fluxes between 1974 and 2001) and the input concentrations expected following load reductions outlined in Table 3-2. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Projected Decline in Input TP No In-Lake Action Alternative 02/03 SYR-12 MFE /Fig 3-1.cdr FOR SFWMD FIGURE 3-1

204 20 Lake Stage (ft NGVD) Year Class Time series of the assumed annual average lake stage in Lake Okeechobee used in the LOWQM and ILPM model simulations. Stage record for the years 2000 to 2112 was developed by looping the 28-year period of record ( ) observed annual average stage back-to-back. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Annual Average Lake Stage Assumed in Model Simulations 02/03 SYR-12 MFE /Fig 3-2.cdr FOR SFWMD FIGURE 3-2

205 60 50 Annual % Frequency of Bloom Occurrence Nearshore TP (mg/l) Havens and Walker (2002) model results predicting the annual frequency of occurrence of algal bloom events exceeding 40 g/l as a function of near-shore TP concentrations. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted Annual Frequency of Algal Bloom Events 02/03 SYR-12 MFE /Fig 3-3.cdr FOR SFWMD FIGURE 3-3

206 150 TSS (mg/l) Time (days) SAV Biomass (g/m2) Day Running Average 60 Day Running Average Time (days) % Cumulative Frequency Distribution Day Running Average 30 Day Running Average SAV Biomass (g/m2) No-action alternative short-term variations in near-shore TSS concentrations and predicted SAV biomass dues to joint variations in TSS and depth. TSS and depth predicted using the LOHTM model; SAV dynamics predicted based on empirical model developed by Havens et al. (in preparation). Upper panel: daily variations in TSS. 2 Middle panel: Variations in SAV biomass (g/m ) presented as 30- and 60-day running averages. Lower panel: Cumulative frequency distribution of predicted SAV biomass. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Short-Term Variations in TSS and SAV 02/03 SYR-12 MFE /Fig 3-4.cdr FOR SFWMD FIGURE 3-4

207 30,000 Particulate P (mg P/kg TSS) 20,000 10,000 0 Enrichment Dilution Redfield Ratio Sediment P TSS (mg/l) Plot of particulate associated phosphorus concentrations (normalized to grams of particulate material present i.e., mg P/kg) versus concentrations of TSS. Lower horizontal bar is predicted concentration assuming all material is resuspended consolidated sediment averaging 1,000 mg P/kg (current concentration in Lake Okeechobee mud zone sediments is 1,144 mg P/kg). Upper horizontal bar is predicted concentration assuming all material is resuspended, unconsolidated detrital algal material characterized by P concentrations consistent with the Redfield ratio (8,732 mg/kg; cf., Stumm and Morgan, 1996). Green squares summer concentrations; blue squares winter concentrations. Red line dilution model fit. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Particulate Phosphorus vs. TSS for Pelagic Stations 1972 to /03 SYR-12 MFE /Fig 3-5.cdr FOR SFWMD FIGURE 3-5

208 Fractional Contribution to TSS Mass FractSed_ Algae FracSed_Sed TSS (mg/l) Fractional Contribution to Resuspended P Frac_P Algae Frac_P Sediment TSS (mg/l) Cumulative Frequency of Relative Contribution to Water Column Particulate P Cum Freq Algae Cum Freq Sed Percent of Resuspended Phosphorus Load Estimated contributions of algal and consolidated resuspension to particulate P burden in water column. Analysis assumes all particulate P derived from either algal resuspension, or resuspension of consolidated surficial sediments. Upper panel: Relative contribution of both material pools to TSS in the water column as a function of increasing TSS. Middle panel: Relative contribution of both material pools to Ppart in the water column as a function of increasing TSS. Lower panel: Weighted contribution (based on frequency of TSS concentration occurrence of algal and consolidated sediment resuspension to Ppart in the water column. Plot indicates that ca. 83% of all resuspended P in Lake Okeechobee derives from resuspended algal material, and only 17% from resuspended consolidated sediment. 02/03 SYR-12 MFE /Fig 3-6.cdr EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Estimated Contribution of Algal and Consolidated Resuspension to Particulate P FOR SFWMD FIGURE 3-6

209 Predicted Lakewater TP (ug P/L) LOWQM ILPM Inflow TP Concentration (ug P/L) 120 ILPM Predicted TP (ug/l) No-Action Alternative 1:1 Agreement Line LOWQM Predicted TP (ug P/L) Comparison of LOWQM and ILPM predicted TP concentrations for long-term simulations. Upper panel: Predicted TP for different input loading scenarios, including the No In-lake Action Alternative. Concentrations are averaged over the last 28 years of the 112-year simulation. Lower panel: ILPM long-term TP concentrations vs. LOWQM long-term TP concentrations. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted TP Concentrations for Long- Term Simulations Model Comparison 02/03 SYR-12 MFE /Fig 3-7.cdr FOR SFWMD FIGURE 3-7

210 100 Long-term Predicted TP (ug P/L) z=2.5 z= Inflow Load TP (ug P/L) Comparison of ILPM predicted quasi steady-state ( time = 120 years) TP concentrations in Lake Okeechobee as a function of surface inflow concentration. Plot shows results of two different types of model runs. The first run uses the currently calibrated model with an exchange depth, z, equal to 5 cm. The second run uses z = 2.5 cm, with the sediment decomposition coefficient, k decomp, increased from 0.2 to 0.4/yr. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Lake TP Concentrations as a Function of Inflow TP Concentrations Model Comparison 02/03 SYR-12 MFE /Fig 3-8.cdr FOR SFWMD FIGURE 3-8

211 % of Steady State Response Line Chloride Model Fractional Response z = 2.5 cm = 8.3 years z=5cm = 24.7 years = 46.2 years TIME (yr) ILPM simulations of response time of Lake Okeechobee lakewater TP concentrations to a stepped reduction in inflow concentration. Shown is the fractional response comparing the change in the time-dependent concentration to the initial concentration and the final concentration predicted at t = 120 years. Three different types of runs are compared: (1) -1 Exchange depth z = 5 cm and kdecomp = 0.2 yr ; (2) z = 2.5 cm and kdecomp = 0.4/yr; and (3) Response of a conservative constituent (e.g., chloride) where response is governed solely by hydraulic residence time of the lake ( = 2.75 yr). w EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Response Time of Lakewater TP Concentrations to Reduction in Inflow TP Concentrations 02/03 SYR-12 MFE /Fig 3-9.cdr FOR SFWMD FIGURE 3-9

212 1.0 Relative Response % Sediment Burial + 10 cm Sediment Box 200% Sediment Burial cm Sediment Box Original Parameterized Model Time (yr) 120 Predicted TP (ug P/L) z = 2.5 cm z=5cm TIME (years) Upper Panel: Sensitivity analysis results. Changes in relative TP concentration (relative to initial conditions) in response to the No In-Lake Action Alternative external load mitigation schedule. Scenario in blue shows the predicted response using the ILPM model under constant hydrologic (long-term average) inputs with no changes in model parameterization. Scenario in green assumes that the depth of active sediment exchange is 10 cm (rather than 5 cm) and the rate of net burial is reduced by a factor of two above the original parameterized value. Scenario in red assumes that the depth of active sediment exchange is 2.5 cm and that the rate of net burial is increased by a factor of two. Lower Panel: Comparison of the predicted time series for changes in lakewater TP predicted by the ILPM for the No In-Lake ActionAlternative for both z = 5 and 2.5 cm. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Sensitivity Analysis Results and Effect of Uncertainty in Exchange Depth (z) 02/03 SYR-12 MFE /Fig 3-10.cdr FOR SFWMD FIGURE 3-10

213 TP (ug/l) Target Goal Pelagic 20 Near-shore Year 30 Annual % Frequency of Occurrence Target Risk Goal Year ILPM model long-term simulation results for the No-Action Alternative. Upper panel: Pelagic and near-shore concentrations of TP. Lower panel: Annual likelihood of algal bloom risk for blooms defined by chlorophyll a concentrations exceeding 40 g/l. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted Long-Term TP Dynamics ILPM Results No In-Lake Action Alternative 02/03 SYR-12 MFE /Fig 3-11.cdr FOR SFWMD FIGURE 3-11

214 150 TP (ug P/L) Pelagic Target TP Goal Near-shore Year 35 Annual % Frequency of Occurrence Target Risk Goal Year LOWQM model long-term simulation results for the No-Action Alternative. Upper panel: Pelagic and near-shore concentrations of TP. Lower panel: Annual likelihood of algal bloom risk for blooms defined by chlorophyll a concentrations exceeding 40 g/l. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted Long-Term Dynamics LOWQM Results No In-Lake Action Alternative 02/03 SYR-12 MFE /Fig 3-12.cdr FOR SFWMD FIGURE 3-12

215 TP (ug P/L) ILPM LOWQM 40 Target Goal Year Time series comparison of pelagic TP concentrations predicted by the LOWQM and ILPM models for the No-Action Alternative. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Time Series Comparison LOWQM vs. ILPM No In-Lake Action Alternative 02/03 SYR-12 MFE /Fig 3-13.cdr FOR SFWMD FIGURE 3-13

216 250 Nearshore P part (ug P/L) Target TP Goal Time (days) Time series predicted by the LOHTM of average near-shore particulate P concentrations derived from sediment resuspension. Ppart concentrations calculated from predicted TSS and the sediment resuspension dilution model (Equation 7). EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Average Particulate P in Near-Shore Region from Sediment Resuspension (LOHTM) 02/03 SYR-12 MFE /Fig 3-14.cdr FOR SFWMD FIGURE 3-14

217 Alum Binding Coefficient Alum_Coeff = *Conc *Conc^2+2.85e-8*Conc^3 Coeff Predicted Coeff Note: Coefficient yields an 80% reduction in internal loading rates of P Surface Inflow Concentration (ug/l) Alum binding coefficient used in the ILPM model as a function of surface inflow concentration. Coefficient has been calibrated to yield a long-term reduction in internal loading of 80% under constant loading conditions. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Alum Binding Coefficient as a Function of Surface Inflow TP Concentration 02/03 SYR-12 MFE /Fig 4-1.cdr FOR SFWMD FIGURE 4-1

218 Begin Alum Dosing Period of Full Alum Efficacy Period of Loss of Alum Efficacy alum Year. Effective alum coefficient,, used in ILPM model as a function of time. alum EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Effective Alum Coefficient in ILPM Model 02/03 SYR-12 MFE /Fig 4-2.cdr FOR SFWMD FIGURE 4-2

219 120 Lakewater TP (ug/l) Period of Alum Dosing No In-Lake Action Chemical Treatment Target TP Year ILPM simulated TP concentrations in the pelagic zone of Lake Okeechobee for the Chemical Treatment and No-Action Alternative scenarios. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Comparison No In-Lake Action vs. Chemical Treatment 02/03 SYR-12 MFE /Fig 4-3.cdr FOR SFWMD FIGURE 4-3

220 Period of Alum Dosing TP (ug P/L) No In-Lake Action 40 Chemical Treatment Target TP Year LOWQM simulated TP concentrations in the pelagic zone of Lake Okeechobee for the Chemical Treatment and No-Action Alternative scenarios. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY LOWQM Comparison No In-Lake Action vs. Chemical Treatment 02/03 SYR-12 MFE /Fig 4-4.cdr FOR SFWMD FIGURE 4-4

221 Period of Alum Dosing TP (mg P/L) LOWQM 40 ILPM Year Comparison of TP concentrations in the pelagic zone of Lake Okeechobee predicted by the ILPM and LOWQM model for the Chemical Treatment scenario. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted TP Concentrations for Chemical Treatment ILPM vs. LOWQM 02/03 SYR-12 MFE /Fig 4-5.cdr FOR SFWMD FIGURE 4-5

222 No Treatment Period of Alum Dosing TP (mg/l) Single Treatment Cycle Multiple Treatment Cycle 40 Target Goal Year This plot compares predicted pelagic lakewater TP concentrations with and without chemical treatment under conditions of a constant surface water input concentration of 157 g/l. Two scenarios of chemical treatment: (1) Single whole-lake dosing (i.e., the Chemical Treatment Alternative) with dosing beginning in 2013; and (2) multiple dosings with alum on a 17-year cycle. The 17-year cycle reflects 2 years to complete the dosing, 8 years of full efficacy, and a following period of 7 years of linearly declining efficacy. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY TP Concentration Comparison No Treatment, Single Treatment, Multiple Treatments 02/03 SYR-12 MFE /Fig 4-6.cdr FOR SFWMD FIGURE 4-6

223 Annual Risk of Bloom Occurrence (%) Period of Alum Dosing No In-Lake Action Chemical Treatment Target Risk Year ILPM simulated annual frequency of algal bloom occurrence (defined as chlorophyll a > 40 g/l) in the near-shore zone of Lake Okeechobee for the Chemical Treatment and No-Action Alternative scenarios. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Annual Algal Bloom Frequency No In-Lake Action vs. Chemical Treatment (ILPM) 02/03 SYR-12 MFE /Fig 4-7.cdr FOR SFWMD FIGURE 4-7

224 Annual Risk of Bloom Occurrence (%) Period of Alum Dosing Chemical Treatment No In-Lake Action Target Risk Year LOWQM simulated annual frequency of algal bloom occurrence (defined as chlorophyll a > 40 g/l) in the near-shore zone of Lake Okeechobee for the Chemical Treatment and No-Action Alternative scenarios. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Annual Algal Bloom Frequency No In-Lake Action vs. Chemical Treatment (LOWQM) 02/03 SYR-12 MFE /Fig 4-8.cdr FOR SFWMD FIGURE 4-8

225 Annual Risk of Bloom Occurrence (%) Period of Alum Dosing LOWQM ILPM Target Risk Year Comparison of ILPM and LOWQM simulated annual frequency of algal bloom occurrence (defined as chlorophyll a > 40 g/l) in the near-shore zone of Lake Okeechobee for the Chemical Treatment scenario. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Annual Algal Bloom Frequency Chemical Treatment (ILPM vs. LOWQM) 02/03 SYR-12 MFE /Fig 4-9.cdr FOR SFWMD FIGURE 4-9

226 Annual Frequency of Bloom Occurrence (%) No In-Lake Action Chemical Treatment % Cumulative Frequency Distribution Cumulative frequency distribution for the simulation period 2012 to 2118 of the probability of algal bloom occurrence in the near-shore zone. Plot compares the cumulative frequency distributions predicted by the ILPM model for both the No- Action and Chemical Treatment scenarios. Data from 2000 through 2011 are excluded because both alternatives are identical during that period (no alum is introduced to the lake before 2012). EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Cumulative Frequency Distribution Algal Bloom Probability (ILPM) 02/03 SYR-12 MFE /Fig 4-10.cdr FOR SFWMD FIGURE 4-10

227 25 Annual Frequency of Algal Bloom Occurrence (%) Target Risk Goal No In-Lake Action Chemical Treatment % Cumulative Frequency Cumulative frequency distribution for the simulation period 2012 to 2118 of the probability of algal bloom occurrence in the near-shore zone. Plot compares the cumulative frequency distributions predicted by the LOWQM model for both the No-Action and Chemical Treatment scenarios. Data from 2000 through 2011 are excluded because both alternatives are identical during that period (no alum is introduced to the lake before 2012). EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Cumulative Frequency Distribution Algal Bloom Probability (LOWQM) 02/03 SYR-12 MFE /Fig 4-11.cdr FOR SFWMD FIGURE 4-11

228 25 Annual Frequency of Algal Bloom Occurrence (%) Target Risk Goal LOWQM ILPM % Cumulative Frequency Comparison of the cumulative frequency distribution for the simulation period 2000 to 2018 of the probability of algal bloom occurrence in the near-shore zone. Plot compares the cumulative frequency distributions predicted by the ILPM and the LOWQM models for the Chemical Treatment scenario. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Cumulative Frequency Distribution Algal Bloom Probability (ILPM vs. LOWQM) 02/03 SYR-12 MFE /Fig 4-12.cdr FOR SFWMD FIGURE 4-12

229

230

231

232 70 60 % Sediment Removed Begin CDF Construction Begin Dredging Conclude Dredging Year Scheduled simulation of the removal of surficial sediment from the mud zone used in ILPM simulations. Plotted is the cumulative extent of areal removal of sediment as a function of time. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Sediment Removal Schedule 02/03 SYR-12 MFE /Fig 5-4.cdr FOR SFWMD FIGURE 5-4

233 120 Lakewater TP (ug/l) Conduct Dredging No Action ILPM Dredge _Sed_753 Dredge _Sed_376 Target TP Year ILPM simulated TP concentrations in the pelagic zone of Lake Okeechobee for the Dredging and No In-Lake Action Alternative scenarios. Two scenarios for dredging are shown: (1) the assumed TP concentration of the residual sediment equals 753 mg/kg; and (2) the assumed TP concentration of the residual sediment equals mg/kg. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Predicted TP Concentrations Dredging vs. No In-Lake Action 02/03 SYR-12 MFE /Fig 5-5.cdr FOR SFWMD FIGURE 5-5

234 160 Lakewater TP (mg/l) Conduct Dredging No Action LOWQM Dredge LOWQM Target TP Year LOWQM simulated TP concentrations in the pelagic zone of Lake Okeechobee for the Dredging and No In-Lake Action Alternative scenarios. The assumed TP concentration of the residual sediment equals 753 mg/kg. The response curves in this plot representing No In-Lake Action and Dredging overlap, making it difficult to distinguish that there are two curves. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY LOWQM Predicted TP Concentrations Dredging vs. No In-Lake Action 02/03 SYR-12 MFE /Fig 5-6.cdr FOR SFWMD FIGURE 5-6

235 Sediment TP (mg/kg) Dredge 7.4%/yr Conduct Dredging No In-Lake Action Dredge 4.5%/yr Year Effect of uncertainty in representing sediment P removal via dredging in the ILPM model predicted sediment TP concentrations as a function of time. Three scenarios are presented: (1) the No In-Lake Action Alternative ( blue); (2) the Dredging Scenario with k = 7.434% year ( red); and the Dredging scenario with k = 4.481% year ( green). dredge dredge EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Uncertainty in Sediment TP Concentrations Dredging Scenario 02/03 SYR-12 MFE /Fig 5-7.cdr FOR SFWMD FIGURE 5-7

236 Lakewater TP (ug/l) Dredge 7.4%/yr Conduct Dredging No In-Lake Action Dredge 4.5%/yr Target Goal Year Effect of uncertainty in representing sediment P removal via dredging in the ILPM model predicted lakewater TP concentrations as a function of time. Three scenarios are presented: (1) the No In-Lake Action Alternative ( blue); (2) the Dredging Scenario with k = 7.434% year ( red); and the Dredging scenario with k = 4.481% year ( green). dredge dredge EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Uncertainty in Lakewater TP Concentrations Dredging Scenario 02/03 SYR-12 MFE /Fig 5-8.cdr FOR SFWMD FIGURE 5-8

237 10 Delta TP (mg/l) Conduct Dredging ILPM % LOWQM ILPM % Year Comparison of LOWQM and ILPM simulated results for the Dredging Alternative. Plot shows the calculated difference between the predicted results for the No In-Lake Action and the Dredging Alternatives for pelagic TP concentrations in Lake Okeechobee. The two curves for the ILPM simulations show the effect of different sediment removal rates. The first curve (shown in blue) assumes that 4.48% of the lake mud zone area would be dredged each year this equates to dredging 67.2% of the mud zone over 15 years. The second curve (shown in red) assumes a dredging rate of 7.34% per year, which would remove 67.2% of the surficial mud zone sediment burden if the sediments redistribute but no further inputs or losses occur. The LOWQM simulation (shown in green) assumes a 4.48%/yr areal dredging rate. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY LOWQM and ILPM Comparison Dredging Alternative 02/03 SYR-12 MFE /Fig 5-9.cdr FOR SFWMD FIGURE 5-9

238 120 Lakewater TP (ug/l) Target TP Year ILPM predicted pelagic lakewater TP concentrations in Lake Okeechobee assuming a surface water input constant concentration of 157 g/l. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Predicted TP Concentration in Lakewater 02/03 SYR-12 MFE /Fig 5-10.cdr FOR SFWMD FIGURE 5-10

239 120 Lakewater TP (ug/l) Conduct Dredging No Dredge Dredge Target TP Year Same as Figure 5-10 except that plot compares predicted pelagic lakewater TP concentrations with and without dredging under conditions of a constant surface water input concentration of 157 g/l. Areal dredging rate = 4.8%/yr of the mud zone. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Predicted Lakewater TP Dredging vs. No Dredging 02/03 SYR-12 MFE /Fig 5-11.cdr FOR SFWMD FIGURE 5-11

240 TSS (mg/l) Run 1 Near Shore Zone TSS Results Run 1A Run 1B Time (days) TSS (mg/l) Run 1 Littoral Zone TSS Results Run 1A Run 1B Time (days) TSS (mg/l) Run 2 Near Shore Zone TSS Results Run 2A Run 2B Time (days) TSS (mg/l) Run 2 Littoral Zone TSS Results Run 2A Run 2B Time (days) TSS (mg/l) Run 3 Near Shore Zone TSS Results Run 3A Run 3B Time (days) TSS (mg/l) Run 3 Littoral Zone TSS Results Run 3A Run 3B Time (days) Variations in predicted near-shore and littoral zone TSS concentrations for the dredging scenarios. Upper panel: Upland CDF. Middle panel: One shoreline CDF. Lower panel: Two island CDFs in the pelagic zone of the lake. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Predicted TSS Concentrations Three Dredging Scenarios 02/03 SYR-12 MFE /Fig 5-12.cdr FOR SFWMD FIGURE 5-12

241 Sediment TP (mg/kg) Dredge 376 Conduct Dredging No In-Lake Action Dredge Year Predicted changes in mud zone sediment TP concentrations for the No In-Lake Action Alternative and the Dredging Alternative. Two scenarios for dredging are shown: (1) the assumed TP concentration of the residual sediment equals 753 mg/kg; and (2) the assumed TP concentration of the residual sediment equals mg/kg. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Comparison of TP Concentrations in Residual Sediment 02/03 SYR-12 MFE /Fig 5-13.cdr FOR SFWMD FIGURE 5-13

242 120 TP (mg/l) Conduct Dredging Target TP 40 Pelagic Nearshore Year ILPM model long-term simulation results for the Dredging Alternative comparing predicted pelagic and near-shore concentrations of TP. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Comparison of TP in Pelagic and Near-Shore Zones 02/03 SYR-12 MFE /Fig 5-14.cdr FOR SFWMD FIGURE 5-14

243 150 TP (mg/l) Conduct Dredging Pelagic Target TP Nearshore Year LOWQM model long-term simulation results for the Dredging Alternative comparing predicted pelagic and near-shore concentrations of TP. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY LOWQM Comparison of TP in Pelagic and Near-Shore Zones 02/03 SYR-12 MFE /Fig 5-15.cdr FOR SFWMD FIGURE 5-15

244 60 Delta TSS (mg/l) A 1B Day 60 Delta TSS (mg/l) A 2B Day 60 Delta TSS (mg/l) A 3B Day Comparison of the difference between the daily average predicted No In-Lake Action TSS for the near-shore zone and the various dredge options. Upper panel: Upland CDF. Middle panel: One shoreline CDF. Lower panel: Two island CDFs in the pelagic zone of the lake. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Near-Shore TSS Comparison 02/03 SYR-12 MFE /Fig 5-16.cdr FOR SFWMD FIGURE 5-16

245 Delta Ppart (mg/l) B A Day Delta Ppart (mg P/L) A Day 2B Delta TP (mg/l) A Day 3B Comparison of the difference between the daily average predicted No In-Lake Action particulate P concentrations for the near-shore zone and the various dredge options. Upper panel: Upland CDF. Middle panel: One shoreline CDF. Lower panel: Two island CDFs in the pelagic zone of the lake. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Near-Shore Particulate P Comparison No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-17.cdr FOR SFWMD FIGURE 5-17

246 1.0 Delta SAV (g/m2) B 1A Day 1.0 Delta SAV (g/m2) B 2A Day Delta SAV (g/m2) A 3B Day Comparison of the difference between the 60-day running average SAV biomass standing 2 crop (g/m ) in the near-shore zone predicted for the No In-Lake Action TSS and the various dredge options. Upper panel: Upland CDF. Middle panel: One shoreline CDF. Lower panel: Two island CDFs in the pelagic zone of the lake. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY SAV Biomass Comparison No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-18.cdr FOR SFWMD FIGURE 5-18

247 Annual Frequency of Occurrence (%) Conduct Dredging No Action ILPM Dredge753 + No Action ILPM Dredge No Action ILPM Target Risk Goal Year ILPM simulated annual frequency of algal bloom occurrence (defined as chlorophyll a > 40 g/l) in the near-shore zone of Lake Okeechobee for the Dredging Treatment and No In-Lake Action Alternative scenarios. Two scenarios for dredging are shown: (1) the assumed TP concentration of the residual sediment equals 753 mg/kg; and (2) the assumed TP concentration of the residual sediment equals mg/kg. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY ILPM Algal Bloom Frequency Comparison No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-19.cdr FOR SFWMD FIGURE 5-19

248 Annual Frequency of Occurrence (%) Conduct Dredging No Action LOWQM Dredge LOWQM Target Risk Goal Year LOWQM simulated annual frequency of algal bloom occurrence (defined as chlorophyll a > 40 g/l) in the near-shore zone of Lake Okeechobee for the Dredging Treatment and No In-Lake Action Alternative scenarios. The assumed TP concentration of the residual sediment equals 753 mg/kg. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY LOWQM Algal Bloom Frequency Comparison No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-20.cdr FOR SFWMD FIGURE 5-20

249 40 35 NoAction AnAve TN:TP Dredging AnAve TN:TP Ratio TN:TP Conduct Dredging Target Goal Year Annual average ratios of TN to TP predicted for the pelagic zone of Lake Okeechobee using the LOWQM for the Dredging and the No In-Lake Action Alternatives. Note that the response curves overlap, making differentiation between the scenarios difficult. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY TN:TP Comparison No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-21.cdr FOR SFWMD FIGURE 5-21

250 20 Annual Frequency of Algal Bloom Occurrence (%) Target Risk Goal No In-Lake Action Dredge 376 Dredge % Cumulative Frequency Cumulative frequency distribution for the simulation period 2012 to 2118 of the probability of algal bloom occurrence in the near-shore zone. Plot compares the cumulative frequency distributions predicted by the ILPM model for both the No In-Lake Action and Dredging scenarios. Data from 2000 through 2011 are excluded because all scenarios are identical during that period. Dredging is assumed to begin Two scenarios for dredging are shown: (1) the assumed TP concentration of the residual sediment equals 753 mg/kg (shown in red) ; and (2) the assumed TP concentration of the residual sediment equals mg/kg (shown in green). EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Cumulative Frequency Distribution of Algal Bloom Occurrence in Near-Shore Zone No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-22.cdr FOR SFWMD FIGURE 5-22

251 25 No In-Lake Action Annual Frequency of Algal Bloom Occurrence (%) Target Risk Goal Dredge % Cumulative Frequency Cumulative frequency distribution for the simulation period 2012 to 2118 of the probability of algal bloom occurrence in the near-shore zone. Plot compares the cumulative frequency distributions predicted by the LOWQM model for both the No In-LakeAction and Dredging scenarios. Data from 2000 through 2011 are excluded because all scenarios are identical during that period. Dredging is assumed to begin in EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Cumulative Frequency Distribution of Algal Bloom Occurrence in Near-Shore Zone No In-Lake Action vs. Dredging 02/03 SYR-12 MFE /Fig 5-23.cdr FOR SFWMD FIGURE 5-23

252 Alternative Relative Performance Dredge 4.5%/yr Dredge 7.4%/yr Chemical Treatment Poorer Performance Relative to NILA Improved Performance Relative to NILA Year Alternative Relative Performance Dredge Chemical Treatment Poorer Performance Relative to NILA Improved Performance Relative to NILA Year Comparison of the efficacy of Chemical Treatment and Dredging alternatives on lakewater TP concentrations relative to the No In-Lake Action (NILA) alternative. Plots show concentrations for both mitigative alternatives normalized to the concentration predicted for No In-Lake Action. In other words, relative concentrations greater than 1 indicate that the alternative predicted higher lakewater TP concentrations than No In-Lake Action, while relative concentrations less than 1 indicate improved performance for the mitigative alternative. Upper panel: ILPM results, including predicted results for dredging the areal extent of the lake mud zone at 4.5 and 7.4% per year. Lower panel: LOWQM results. EVALUATION OF ALTERNATIVES LAKE OKEECHOBEE SEDIMENT MANAGEMENT FEASIBILITY STUDY Relative Comparison of Alternative Performance 02/03 SYR-12 MFE /Fig 6-1.cdr FOR SFWMD FIGURE 6-1