Urban Stormwater BMP Performance Monitoring

Transcription

1 Urban Stormwater BMP Performance Monitoring Prepared by Geosyntec Consultants and Wright Water Engineers, Inc. Prepared under Support from U.S. Environmental Protection Agency Water Environment Research Foundation Federal Highway Administration Environmental and Water Resources Institute of the American Society of Civil Engineers June 2009

2 Disclaimer This report was prepared by the organization(s) named below as an account of work sponsored by the Water Environment Research Foundation (WERF) and its partners on the International Stormwater Best Management Practices Database project. WERF s partners on the project include the U.S. Environmental Protection Agency (U.S. EPA), the Federal Highway Administration (FHWA), and the American Society of Civil Engineers Environmental Water Resources Institute (ASCE-EWRI). Neither WERF, its partners on the project, members of WERF or ASCE-EWRI, the organization(s) named below, nor any person acting on their behalf: (a) makes any warranty, express or implied, with respect to the use of any information, apparatus, method, or process disclosed in this report or that such use may not infringe on privately owned rights; or (b) assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method, or process disclosed in this report. Geosyntec Consultants Wright Water Engineers, Inc. The views expressed in this document are solely those of organizations named above and neither WERF nor its partners endorse any products or commercial services mentioned in this publication. Mention of trade names or commercial products does not constitute WERF s nor its partner s endorsement or recommendations for use. Similarly, omission of products or trade names indicates nothing concerning WERF s nor partner s positions regarding product effectiveness or applicability.

3 TABLE OF CONTENTS Acknowledgements Executive Summary Chapter 1 Introduction 1.1 Purpose of this Manual Manual Overview Stormwater Basics Physical and Chemical Characteristics of Stormwater Runoff Best Management Practices Stormwater BMP Monitoring The International Stormwater BMP Database Regulatory Environment Manual Scope Limitations References Chapter 2 Developing a Monitoring Plan 2.1 Step 1. Define Study Opjectives/State the Problem Key Activities for Step Outputs from Step Step 2. Identify Study Goals Key Activities for Step Outputs from Step Step 3. Identify Information Inputs Key Activities for Step Determining Number of Storms Needed for Meaningful Statistical Assessment General Considerations Sampling Strategies and Determination of Number of Samples for Paired Evaluations Outputs from Step Step 4. Define the Boundaries of the Study Key Activities for Step Outputs from Step Step 5. Develop the Analytical Approach Key Activities for Step Outputs from Step Step 6. Specify Performance or Acceptance Criteria Key Activities for Step Outputs from Step Step 7. Develop the Plan for Obtaining Data Key Activities for Step Urban Stormwater BMP Performance Monitoring Manual January 2009 TOC Page TOC-1

4 Table of Contents Outputs from Step Step 8. Assess Reasonableness of Plan and Refine Key Activities for Step Outputs from Step Conclusion References Chapter 3 Hydrologic and Hydraulic Monitoring 3.1 Meteorological Data Collection Precipitation Types of Precipitation Gages Site Proximity Number of Gages Collection of Other Meteorological Data Atmometers Weather Stations Flow Measurement Methods Primary Flow Measurement Devices Weirs Flumes Selection Considerations Secondary Flow Measurement Devices Float Gage Bubbler Tube Ultrasonic Depth Sensor Pressure Probe Ultrasonic Uplooking Radar/Microwave Velocity-Based Methods Ultrasonic (Doppler) Sensors Electromagnetic Sensors Acoustic Path Rotating-Element Current Meters Pressure Sensors Acoustical Sensors Float-and-Stopwatch Method Head Stick Estimated Flow Deflection (or Drag-Body) Method Tracer Studies Methods Suitable for Calibration Data Loggers Programmability Data Capacity Communications Power Requirements Urban Stormwater BMP Performance Monitoring Manual June 2009 TOC Page TOC-2

5 Table of Contents Other Flow Measurement Methods Direct Measurement Methods Tracer Dilution Methods Pump Discharge Method Stage-Based Variable Gate Meters Stage-Based Equations QA/QC of Flow Measurements Infiltration Estimates Common Flow Monitoring Challenges for LID Techniques Conclustion References Chapter 4 Water Quality Monitoring 4.1 Water Quality Parameters and Analytical Methods Selecting Parameters Dissolved vs. Total Metals Measurement of Suspended Solids Concentration Measurement of Gross Solids Microbiological Sampling Analytical Methods Sampling Location Upstream Downstream Intermediate Locations Water Quality Sample Collection Techniques Grab Samples Composite Samples Automated Sampling Automated Sampling Equipment In-Situ Water Quality Devices Remote Communication with Automatic Equipment Manual Sampling Manual Grab Sampling Equipment Manual Composite Sampling Equipment Sediment Sampling Soil (Infiltration Media) Sampling Groundwater Sampling QA/QC for Water Quality Sampling Sampling Methods Grab Sample Collection Techniques Contamination/Blanks Reconnaissance and Preparations Laboratory Coordination Sample Containers/Preservation/Holding Times Field QA/QC Procedures Laboratory QA/QC Procedures Urban Stormwater BMP Performance Monitoring Manual June 2009 TOC Page TOC-3

6 Table of Contents 4.10 Conclusion Refererences Chapter 5 Implementation of Monitoring Plan 5.1 Training of Personnel Installation of Equipment Testing and Calibrating Equipment Conducting Monitoring Coordinating Laboratory Analysis Conclusion References Chapter 6 Data Management, Validation and Reporting 6.1 Recommendations for Data Management Data Validation Using or Establishing Databases Data Entry Approaches QA/QC Techniques Outlier Screening/Analysis Preliminary Data Evaluation Reporting Results Submitting Data to the International Stormwater BMP Database Overview of Data Requirements for the BMP Database General Test Site Information Monitored Events Watershed Information General BMP Information Monitoring Stations Monitoring Results Conclusion References Chapter 7 BMP Performance Analysis (Chapter Not Yet Released) 7.1 Concentrations, Loads, and Volume Reductions Concentrations Contaminant Loads Event Mean Concentrations Volume Reductions Data Analysis and Underlying Principles Descriptive Statistics Parametric Statistics Non-parametric Statistics Relevance of the Lognormal Distribution Comparative Statistics and Hypothesis Tests... Urban Stormwater BMP Performance Monitoring Manual June 2009 TOC Page TOC-4

7 Table of Contents Independent Data Sets Paired Data Sets Graphical Data Analysis Histograms Box plots Quantile Plots and Probability Plots Scatter Plots Analysis of Censored Data Simple Substitution Maximum Likelihood Estimation (MLE) Regression on Order Statistics (ROS) Kaplan-Meier (K-M) Recommended Approach for Handling Nondetects Bootstrap Methods Error Analysis and Measurement Accuracy Expressing Errors Propagation of Errors Performance of BMP and BMP Systems Comparative Measures of BMP Efficiency Multivariate and Non-Linear Model Reference Watershed Methods Effluent Probability Method Statistical Measures Employed by the BMP Database Statistical Distribution of Water Quality Data Influent and Effluent Scatter Plots Box Plots Probability Plots Overview of Results of Efficiency and Effluent Quality by BMP Type and Parameter... Chapter 8 Low Impact Development Monitoring (Chapter Not Yet Released) 8.1 Introduction to LID Basic LID Concepts What distinguishes an LID Site? LID Monitoring Philosophy Site Level LID Monitoring Challenges Monitoring Study Design for LID Projects Use of Reference Watersheds LID Watershed Characteristics Watershed Geometry Vegetative Cover and Land Uses Imperviousness and Connectivity Soil Properties and Groundwater Conditions Composite Site Characteristics and Hydrologic Performance Metrics Hydrologic Characterization... Urban Stormwater BMP Performance Monitoring Manual June 2009 TOC Page TOC-5

8 Table of Contents General Water Balance Regional Water Balance Thornthwaite Monthly Water Balance Long Term Monitoring and Data Representativeness Data Collection and Reporting International Stormwater BMP Database Requirements for LID Impervious Surface Data Collection Hydrologic Data Collection Quantifying Infiltration Quantifying Evapotranspiration Water Quality Data Collection Cost Data Data Interpretation and Performance Evaluation Drawing Appropriate Conclusions Regarding Volume Reduction Characterizing Results Based on Storm Characteristics Comparing Performance to Design Objectives and Criteria Accounting for Uncertainty/Error Water Quality Benefits and Load Reduction Comparing Surface Water Discharge Loads to Storm Characteristics Accounting for Uncertainty and Error Groundwater Potential Impacts Comparison of LID to other BMPs LID Monitoring Case Studies Cross Plains, WI Burnsville, MN Jordan Cove, CT Somerset, MD... Appendices Appendix A Stormwater BMP Database Reporting Parameters Appendix B Assessment of Approaches to Evaluating BMP Performance Appendix C Error Analysis Appendix D Number of Samples Required for Various Powers, Confidence Intervals and Percentile Differences Appendix E Derivation of the Number of Samples Required to Measure a Statistical Difference in Population Means Appendix F Relationship of Log-Normal Distributions Urban Stormwater BMP Performance Monitoring Manual June 2009 TOC Page TOC-6

9 ACKNOWLEDGEMENTS The 2009 update to this monitoring manual was made possible through funding from the U.S. Environmental Protection Agency (USEPA) under USEPA Contract No. EP-C managed by John Kosco, Tetra Tech, and a coalition of sponsors led by the Water Environment Research Foundation (WERF), managed by Jeff Moeller, WERF. WERF partners included the Federal Highway Administration (FHWA) and the American Society of Civil Engineers (ASCE) Environmental and Water Resources Institute (EWRI). This manual expands and significantly revises the manual Urban Stormwater BMP Performance Monitoring: A Guidance Manual for Meeting the National Stormwater BMP Database Requirements (EPA-821-B ) prepared in 2002 by Geosyntec Consultants, Urban Drainage and Flood Control District and the Urban Water Resources Research Council (UWRRC) of ASCE in cooperation with the USEPA Office of Water. Project Sponsors Nikos Singelis, USEPA, Office of Pesticides (formerly Office of Wastewater Management) Lisa Hair, P.E., USEPA, Office of Wetlands, Oceans and Watersheds Robert Goo, USEPA, Office of Wetlands, Oceans and Watersheds Jack Faulk, USEPA, Office of Wastewater Management John Kosco, P.E., Tetra Tech (Project Manager for EPA) Jeff Moeller, P.E., Water Environment Research Foundation Brian Parsons, P.E., Environmental and Water Resources Institute, American Society of Civil Engineers Patricia Cazenas, P.E., Federal Highway Administration Eric Strassler, USEPA, Office of Water/Office of Science & Technology Project Team Marcus Quigley, P.E., Geosyntec Consultants Jane Clary, LEED AP, CPESC, Wright Water Engineers, Inc. Andrew Earles, P.E., Ph.D., Wright Water Engineers, Inc. Marc Leisenring, Geosyntec Consultants Eric Strecker, P.E., Geosyntec Consultants Jonathan Jones, P.E., Wright Water Engineers, Inc. John O Brien, Wright Water Engineers, Inc. Expert Advisory Panel and Contributors Richard Horner, Ph.D., University of Washington William Hunt, P.E., Ph.D., North Carolina State University Robert Pitt, P.E., Ph.D., DEE, University of Alabama Robert Roseen, P.E. Ph.D., University of New Hampshire Robert Traver, P.E., Ph.D., Villanova University Ben Urbonas, P.E., Urban Watersheds Research Institute Urban Stormwater BMP Performance Monitoring Manual June 2009 Acknowledgements Page ACK-1

10 Acknowledgements Urban Water Resources Research Council Reviewers and Contributors Shirley Clark, P.E., Ph.D., Pennsylvania State University James Lenhart, P.E., D.WRE, Contech Betty Rushton, P.E., Ph.D., University of Florida Scott Struck, Ph.D., Tetra Tech M.S. Cheng, Prince George s County, Maryland Elizabeth Fassman, Ph.D., University of Auckland Thomas O Connor, USEPA Water Environment Research Foundation Project Subcommittee Members and Reviewers Gregory Granato, U.S. Geological Survey (Reviewer) Michael Barrett, P.E., Ph.D., University of Texas (Reviewer) David Graves, CPESC, CPSWQ, New York State Department of Transportation (Reviewer) Jesse Pritts, P.E., USEPA Bob Carr, P.E., Water Resources Modeling Urban Stormwater BMP Performance Monitoring Manual June 2009 Acknowledgements Page ACK-2

11 EXECUTIVE SUMMARY Over the past three decades, both public and private entities have monitored urban stormwater Best Management Practices (BMPs) for many purposes, often related to efforts to comply with the continually evolving federal Clean Water Act. In 1996, the U.S. Environmental Protection Agency (EPA) entered into a cooperative agreement with the American Society of Civil Engineers (ASCE), led by members of the Urban Water Resources Research Council (UWRRC), to initiate the International Stormwater BMP Database project ( BMP Database ). The BMP Database goals were multi-faceted, with key goals including development of a standardized set of monitoring and reporting protocols for urban stormwater BMP performance studies and assembling and summarizing historical and ongoing BMP study data into a standardized format to facilitate performance analysis. During the initial stages of the BMP Database project, it became clear that better guidance was needed regarding stormwater BMP monitoring, particularly if monitoring results were to be valuable to the broader technical, management, and regulatory community. As a result, the 2002 version of this monitoring manual was developed to promote collection of more useful and representative data associated with BMP studies, as well as more consistent reporting of monitoring results appropriate for inclusion in the BMP Database. Since that time, both the BMP Database project and stormwater management practices have continued to evolve, prompting this second release of the manual. The purposes of this updated Manual are primarily two-fold: 1) Improve the state of the practice by providing and enhancing a recommended set of protocols and standards for collecting, storing, analyzing, and reporting stormwater BMP monitoring data that will lead to better understanding of the function, efficiency, and design of urban stormwater BMPs. 2) Provide monitoring guidance for Low Impact Development (LID) strategies at the overall site level (e.g., monitoring overall sites with multiple distributed stormwater controls). The audience for this Manual is targeted primarily to those who possess a basic level of knowledge regarding stormwater quality, hydrology, and regulatory issues. The EPA website ( and other state and local websites can be referenced for additional guidance and background information. This Manual provides guidance for all stages of BMP monitoring programs ranging from the early stages of study design to the end stages of data interpretation and reporting. Guidance is provided for monitoring a broad range of individual BMPs as well as overall site monitoring with multiple distributed BMPs, such as is the case with LID sites. This Manual focuses primarily on the collection, reporting, and analysis of water quantity and quality measurements at the heart of quantitative BMP efficiency projects. It does not address, in detail, sediment sampling methods and techniques, biological assessment, monitoring of receiving waters, monitoring of groundwater, streambank erosion, channel instability, channel morphology, or other activities that in many circumstances may be as, or more, Urban Stormwater BMP Performance Monitoring Manual June 2009 Executive Summary Page ES-1

12 Executive Summary useful for measuring and monitoring water quality for assessing BMP efficiency. In some cases, references for additional information on these subjects have been provided. The Manual focuses on these topics: 1) Designing the Monitoring and Reporting Program (Chapter 2): A well-thought out and systematically designed monitoring program is essential to a cost-effective study design that yields meaningful results. The Manual builds upon guidance provided by EPA (2002) in its Guidance for Quality Assurance Project Plans, providing additional guidance specific to stormwater BMP monitoring and the BMP Database protocols. 2) 3) 4) Methods and Equipment for Stormwater BMP Monitoring (Chapters 3 and 4) : In order to obtain high-quality data in BMP monitoring studies, it is necessary to select the proper precipitation, flow, and water quality sample collection and monitoring equipment and procedures. Chapter 3 provides information and guidance related to flow and precipitation monitoring in the context of BMP monitoring, and Chapter 4 focuses on water quality sample collection and analysis methods. Implementing the Monitoring Program (Chapter 5) : In order for well designed monitoring programs to result in high quality data, personnel must be properly trained, equipment be properly installed, calibrated and maintained, samples be correctly collected and analyzed, and data properly reported. Failures at this stage of the monitoring program can result in data that cannot be used to draw valid conclusions regarding BMP performance. Data Management, Evaluation and Reporting of Results (Chapter 6): Once data have been collected from a monitoring program, the data need to be compiled and managed in a manner that reduces introduction of errors and enables ready access for future reference, and ideally, facilitates incorporation into the BMP Database ( A strong data management and reporting system helps to ensure that studies are documented in a manner that enables long-term use of the data and transferability to the local, regional, national, and international state of the practice. As part of this chapter, an overview of data reporting requirements for the BMP Database is provided, describing study features such as test site, watershed, and BMP design characteristics, instrumentation, and monitoring data (precipitation, flow, water quality). 5) BMP Performance Analysis (Chapter 7) : Over the past decade, the BMP Database project has developed recommended performance analysis approaches for BMP studies. This chapter describes these methods, as well as pitfalls to avoid misleading interpretation of data. 6) Low Impact Development(LID)/Distributed Controls Monitoring (Chapter 8): Building upon the concepts introduced for monitoring individual BMPs, this chapter provides guidance on specific challenges associated with monitoring distributed controls at the site level, particularly focused on LID. In these types of studies, a variety of practices such as amending soils to promote infiltration of runoff, Urban Stormwater BMP Performance Monitoring Manual June 2009 Executive Summary Page ES-2

13 Executive Summary disconnecting impervious areas, use of pervious paving materials, implementation of rain gardens on multiple lots, use of swales instead of curb and gutter, and other runoff reduction practices may be implemented. As a result, unique challenges exist in collecting and analyzing the performance of such sites. Although the state of the practice continues to evolve on this topic, this chapter provides basic guidance on properly designing such studies and suggests approaches for meaningful data interpretation. 7) Supplemental Resources on Key Topics (Appendices): Many of the topics addressed in this manual are complex and/or require considerable detail for proper discussion. For this reason, supplemental appendices are provided as follows: Appendix A: Data Entry Forms for International Stormwater BMP Database: Forms useful for recording BMP monitoring study information, key watershed and BMP design criteria, instrumentation and monitoring data for precipitation, flow, and water quality are summarized in Appendix A, corresponding to the data entry spreadsheets used in the BMP Database. The Stormwater BMP Database website ( should be referenced to obtain the most current version of these spreadsheets for data entry. Appendix B: Comparison of Data Analysis Approaches: This appendix contains a discussion of the various BMP performance analysis approaches that have been commonly used historically, but are not currently recommended by the BMP Database project. Nonetheless, some of these techniques are used by others, so comments are provided regarding the strengths and weaknesses of each approach. Appendix C: Determining Required Number of Samples: Depending on the objectives established for the monitoring program, the number of samples required for meaningful interpretation of the data can vary substantially. This appendix provides guidance in determining the number of samples needed to obtain statically significant monitoring data. It also includes charts for estimating the number of samples required to observe a statically significant difference between two populations for a various levels of confidence and power. Appendix D: Error Analysis: Properly accounting for errors and uncertainty in BMP monitoring data is important to avoid erroneous conclusions regarding BMP performance. This appendix describes methods for calculating expected errors in field measurements. Appendices E and F: Statistical Information: Although this manual does not provide a primer on statistics, Appendix E provides some basic information needed to properly apply statistics in the context of stormwater BMP monitoring. For example, a table for estimating arithmetic descriptive statistics based on descriptive statistics of log-transformed data is included. Appendix F provides basic information related to log-normal distributions. Urban Stormwater BMP Performance Monitoring Manual June 2009 Executive Summary Page ES-3

14 Executive Summary This Manual addresses methods that were in use at the time it was written. As the state of the practice and the design of monitoring equipment progress, new monitoring approaches and techniques, more sensitive devices, and equipment based on new technologies will likely be employed. Although the technology may change somewhat from that described herein, most of the basic flow and water quality monitoring methods discussed in this document have a long history of use and will most likely remain viable even as new and different technologies emerge. Urban Stormwater BMP Performance Monitoring Manual June 2009 Executive Summary Page ES-4

15 Chapter 1 INTRODUCTION 1.1 Purpose of this Manual Over the past three decades, both public and private entities have monitored urban stormwater Best Management Practices (BMPs) for many purposes, often related to efforts to comply with the continually evolving federal Clean Water Act. In 1996, the U.S. Environmental Protection Agency (EPA) entered into a cooperative agreement with the American Society of Civil Engineers (ASCE), led by members of the Urban Water Resources Research Council (UWRRC), to initiate the International Stormwater BMP Database project ( BMP Database ). The BMP Database goals were multi-faceted, with key goals including development of a standardized set of monitoring and reporting protocols for urban stormwater BMP performance studies and assembling and summarizing historical and ongoing BMP study data into a standardized format to facilitate performance analysis. During the initial stages of the BMP Database project, it became clear that better guidance was needed regarding stormwater BMP monitoring, particularly if monitoring results were to be valuable to the broader technical, management, and regulatory community. As a result, the 2002 version of this monitoring manual was developed to promote collection of more useful and representative data associated with BMP studies, as well as more consistent reporting of monitoring results appropriate for inclusion in the BMP Database. Since that time, both the BMP Database project and stormwater management practices have continued to evolve, prompting this second release of the manual. The purposes of this updated Manual are primarily two-fold: 1) Improve the state of the practice by providing and enhancing a recommended set of protocols and standards for collecting, storing, analyzing, and reporting stormwater BMP monitoring data that will lead to better understanding of the function, efficiency, and design of urban stormwater BMPs. 2) Provide monitoring guidance for Low Impact Development (LID) strategies at the overall site level (e.g., monitoring overall sites with multiple distributed stormwater controls). The remainder of this introduction provides a brief synopsis of the organization and content of this Manual, and provides some basic information on stormwater, BMPs, the BMP Database project, and regulatory drivers related to BMP implementation and monitoring. Several key terms used throughout this manual are defined, and links to other monitoring resources are also provided. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-1

16 Introduction 1.2 Manual Overview This Manual provides guidance for all stages of BMP monitoring programs ranging from the early stages of study design to the end stages of data interpretation and reporting. Guidance is provided for monitoring a broad range of individual BMPs as well as overall site monitoring with multiple distributed BMPs, such as is the case with LID sites. The Manual addresses these topics: 1) Designing the Monitoring and Reporting Program (Chapter 2): A well-thought out and systematically designed monitoring program is essential to a cost-effective study design that yields meaningful results. The Manual builds upon guidance provided by EPA (2002) in its Guidance for Quality Assurance Project Plans, providing additional guidance specific to stormwater BMP monitoring and the BMP Database protocols. 2) 3) 4) Methods and Equipment for Stormwater BMP Monitoring (Chapters 3 and 4) : In order to obtain high-quality data in BMP monitoring studies, it is necessary to select the proper precipitation, flow, and water quality sample collection and monitoring equipment and procedures. Chapter 3 provides information and guidance related to flow and precipitation monitoring in the context of BMP monitoring, and Chapter 4 focuses on water quality sample collection and analysis methods. Implementing the Monitoring Program (Chapter 5) : In order for well designed monitoring programs to result in high quality data, personnel must be properly trained, equipment be properly installed, calibrated and maintained, samples be correctly collected and analyzed, and data properly reported. Failures at this stage of the monitoring program can result in data that cannot be used to draw valid conclusions regarding BMP performance. Data Management, Evaluation and Reporting of Results (Chapter 6): Once data have been collected from a monitoring program, the data need to be compiled and managed in a manner that reduces introduction of errors and enables ready access for future reference, and ideally, facilitates incorporation into the BMP Database ( A strong data management and reporting system helps to ensure that studies are documented in a manner that enables long-term use of the data and transferability to the local, regional, national, and international state of the practice. As part of this chapter, an overview of data reporting requirements for the BMP Database is provided, describing study features such as test site, watershed, and BMP design characteristics, instrumentation, and monitoring data (precipitation, flow, water quality). 5) BMP Performance Analysis (Chapter 7): Over the past decade, the BMP Database project has developed recommended performance analysis approaches for BMP studies. This chapter describes these methods, as well as pitfalls to avoid misleading interpretation of data. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-2

17 Introduction 6) Low Impact Development(LID)/Distributed Controls Monitoring (Chapter 8) : Building upon the concepts introduced for monitoring individual BMPs, this chapter provides guidance on specific challenges associated with monitoring distributed controls at the site level, particularly focused on LID. In these types of studies, a variety of practices such as disconnecting impervious areas, use of pervious paving materials, implementation of rain gardens on multiple lots, use of swales instead of curb and gutter, and other runoff reduction practices may be implemented. As a result, unique challenges exist in collecting and analyzing the performance of such sites. Although the state of the practice continues to evolve on this topic, this chapter provides basic guidance on properly designing such studies and suggests approaches for meaningful data interpretation. 7) Supplemental Resources on Key Topics (Appendices): Many of the topics addressed in this manual are complex and/or require considerable detail for proper discussion. For this reason, supplemental appendices are provided as follows: Appendix A: Data Entry Forms for International Stormwater BMP Database: Forms useful for recording BMP monitoring study information, key watershed and BMP design criteria, instrumentation and monitoring data for precipitation, flow, and water quality are provided in Appendix A, corresponding to the data entry spreadsheets used in the BMP Database. Appendix B: Comparison of Data Analysis Approaches: This appendix contains a discussion of the various BMP performance analysis approaches that have been commonly used historically, but are not currently recommended by the BMP Database project. Nonetheless, some of these techniques are used by others, so comments are provided regarding the strengths and weaknesses of each approach. Appendix C: Determining Required Number of Samples: Depending on the objectives established for the monitoring program, the number of samples required for meaningful interpretation of the data can vary substantially. This appendix provides guidance in determining the number of samples needed to obtain statically significant monitoring data. It also includes charts for estimating the number of samples required to observe a statically significant difference between two populations for a various levels of confidence and power. Appendix D: Error Analysis: Properly accounting for errors and uncertainty in BMP monitoring data is important to avoid erroneous conclusions regarding BMP performance. This appendix describes methods for calculating expected errors in field measurements. Appendices E and F: Statistical Information: Although this manual does not provide a primer on statistics, Appendices E and F provide some basic information needed to properly apply statistics in the context of stormwater BMP monitoring.` Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-3

18 Introduction 1.3 Stormwater Basics Exhibit 1-1. Defining Stormwater Physical and Chemical Characteristics of Stormwater Runoff Numerous studies conducted since the late 1970s show that stormwater runoff from urban and industrial areas is a potentially significant source of pollution (EPA 1983; Driscoll et al. 1990; Pitt et al. 2008). As a result, federal, state, and local regulations have been promulgated to address stormwater quality and many communities have implemented structural and non-structural stormwater BMPs to minimize the potential adverse impacts of urban runoff and comply with these regulations. Although the historical focus of many monitoring programs was primarily stormwater quality (chemical), more recently, the hydrologic and hydraulic (physical) changes in watersheds associated with urbanization are increasingly being recognized as significant contributors to receiving water degradation. Representative physical impacts include stream channel changes (erosion, sedimentation, temperature changes), as well as wetland water level fluctuations. As a result, site designs such as LID that seek to mimic predevelopment site hydrology are being encouraged or mandated by more communities. Some of the challenges associated with proper characterization of stormwater quality are related to its highly variable nature (EPA 1983; Driscoll et al. 1990). For example, the intensity of rainfall often Although in the simplest sense, stormwater can be defined as runoff resulting from rainfall or snowmelt, a more inclusive definition is used in this Monitoring Manual. In the context of stormwater BMP monitoring, stormwater also includes base flows or dry weather flows occurring prior to, during and following storm runoff events, as well as other discharges affecting the BMP such as materials that are dumped, leaked, spilled, or otherwise discharged into the conveyance system. Representative dry weather flows include pavement washing, pavement cutting wash water, or irrigation water, including the pollutants transported in such flows. In some cases, dry weather loads can greatly exceed wet weather loads over the course of a year and must be taken into account in BMP monitoring programs. Stormwater may also contain materials that settled out in the system toward the end of previous storms and are flushed out by high flows during the event being sampled. varies irregularly and dramatically. These variations in rainfall intensity affect runoff rate, pollutant washoff rate, in-channel flow rate, pollutant transport, sediment deposition and resuspension, channel scour, and numerous other phenomena that collectively determine the pollutant concentrations, pollutant forms, and stormwater flow rate observed at a given monitoring location at any given moment. In addition, the transitory and unpredictable nature of many pollutant sources and release mechanisms (e.g., spills, leaks, dumping, construction activity, landscape irrigation runoff, vehicle washing runoff), and differences in the time interval between storm events also contribute to inter-storm variability. As a result, pollutant concentrations and other stormwater characteristics at a given location often fluctuate greatly during a single storm runoff event and from event to event. It is important that those involved with stormwater monitoring not underestimate the complex variables affecting stormwater BMP monitoring. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-4

19 Introduction Best Management Practices In the context of post-construction urban stormwater runoff management, Best Management Practices (BMPs) include a variety of measures intended to prevent or reduce the discharge of pollutants to waters of the United States. BMPs can be discussed in terms of individual structural practices and non-structural practices, as well as in terms of overall site designs such as LID that combine a variety of structural and non-structural practices. Structural BMPs include a variety of practices that rely on a wide range of hydrologic, physical, biological, and chemical processes to improve water quality and manage runoff. (See Exhibit 1-2 and Critical Assessment of Stormwater Treatment and Control Selection Issues [WERF 2005] for more information on these processes.) Non-structural BMPs such as education and source control ordinances typically depend on a combination of behavioral change and enforcement. Due to the variation in BMP designs and features, as well as rainfall distributions, there is not a one-size-fits-all monitoring strategy. For example, Philadelphia, PA, receives approximately 45 inches of rainfall a year, primarily in small storms, whereas Austin receives approximately 35 inches of rainfall, but primary in large storms, whereas Denver receives approximately 14 inches per year. These differences in rainfall distributions affect both the design of BMPs and the design of monitoring programs. Many BMPs and LID sites are designed to treat runoff from small storms, rather than large storms, so it is important to understand the basis of design for BMPs when developing monitoring programs and evaluating performance of BMPs. In this Manual, five general categories of BMPs will be used to assist in monitoring strategy design and BMP performance analysis. These general categories include: Type I Type II BMPs with well-defined inlets and outlets (e.g., detention basins, vegetated swales, catch basin inserts). These are the easy BMPs to monitor where inflow and outflow can typically be paired to assess performance. In the case of systems such as wet ponds with substantial residence times or storage volumes, data may be straightforward to collect, but challenging to evaluate for individual storms. In such cases, a seasonal mass balance approach is often more appropriate than a storm-based, paired influent-effluent approach because it is likely that the effluent sample for small storms is displaced water originating from prior events. BMPs with well-defined inlets, but not outlets (e.g., infiltration basins, infiltration trenches, bioretention cells). Monitoring strategies for these BMPs are more complex and may involve sampling of underdrains, vadose (unsaturated) zone monitoring, groundwater monitoring, measuring infiltration rates and surface overflow. At a minimum, the influent and surface overflow must be quantified, since the difference between the two should represent the volume infiltrated. If an underdrain is used to direct partially treated water back to the surface drainage, then it should also be monitored. Evaluation of data from these types of studies should focus on mass balance approaches. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-5

20 Introduction Type III BMPs with well-defined outlets, but not inlets (e.g., grass swales where inflow is overland flow along the length of the swale, buffer strips, green roofs). Type IV BMPs without any well-defined inlets or outlets and/or institutional BMPs (e.g., buffer strips, basin-wide catch basin retrofits, education programs, source control programs, disconnected impervious area practices). Type V Low Impact Development/Distributed Controls/Overall Site Designs where some defined monitoring locations are available that may include monitoring of individual practices within a development, in combination with an overall site monitoring mechanism. In addition to understanding the complexities associated with monitoring the various types of BMPs, it is also important to recognize that there is a difference between reporting performance based on the flows treated by the BMP and the flows associated with the overall BMP system, which includes bypassed flows and overflows. These types of considerations are also important when assessing the performance of the BMP, the effectiveness of the overall BMP system and the efficiency of the BMP or BMP system in removing pollutants. Definitions of several BMP-related terms used throughout this document are provided in Exhibit 1-3. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-6

21 Introduction Exhibit 1-2. Structural Stormwater Controls and Associated Fundamental Process Categories (Source: WERF Critical Assessment of Stormwater Treatment and Control Selection Issues. 02-SW-1.) Fundamental Process Category (FPC) Hydrologic Operations Physical Treatment Operations Biological Processes Chemical Processes Unit Operation or Process (UOP) Target Pollutants Flow and Volume Attenuation Volume Reduction All pollutant loads Particle Size Alteration Coarse sediment Physical Sorption Nutrients, metals, petroleum compounds Size Separation and Exclusion (screening and filtration) Coarse sediment, trash, debris Density, Gravity, Inertial Separation (grit separation, sedimentation, flotation and skimming, and clarification) Sediment, trash, debris, oil and grease Aeration and Volatilization Oxygen demand, PAHs, VOCs Physical Agent Disinfection Pathogens Microbially Mediated Transformation (can include oxidation, reduction, or facultative processes) Metals, nutrients, organic pollutants Uptake and Storage Metals, nutrients, organic pollutants Chemical Sorption Processes Metals, nutrients, organic pollutants Coagulation/Flocculation Fine sediment, nutrients Ion Exchange Metals, nutrients Chemical Disinfection Pathogens Typical Treatment System Components (TSCs) Extended detention basins Retention/detention ponds Wetlands Tanks/vaults Equalization basins Infiltration/exfiltration trenches and basins Permeable or porous pavement Bioretention cells Dry swales Dry well Extended detention basins Comminutors (not common for stormwater) Mixers (not common for stormwater) Engineered media, granular activated carbon, and sand/gravel (at a lower capacity) Screens/bars/trash racks Biofilters Permeable or porous pavement Infiltration/exfiltration trenches and basins Manufactured bioretention systems Engineered media/granular/sand/compost filters Hydrodynamic separators Catch basin inserts (i.e., surficial filters) Extended detention basins Retention/detention ponds Wetlands Settling basins, Tanks/vaults Swales with check dams Oil-water separators Hydrodynamic separators Sprinklers Aerators Mixers (not common for stormwater) Shallow detention ponds Ultra-violet systems Wetlands Bioretention systems Biofilters (and engineered bio-media filters) Retention ponds Media/sand/compost filters Wetlands/wetland channels Bioretention systems Biofilters Retention ponds Subsurface wetlands Engineered media/sand/compost filters Infiltration/exfiltration trenches and basins Detention/retention ponds Coagulant/flocculant injection systems Engineered media, zeolites, peats, surface complexation media Custom devices for mixing chlorine or aerating with ozone Advanced treatment systems Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-7

22 Introduction Exhibit 1-3. Key Terms Used in this Manual A common understanding of terms used in this manual includes the following: Best Management Practice (BMP) A device, practice, or method for removing, reducing, retarding, or preventing targeted stormwater runoff constituents, pollutants, and contaminants from reaching receiving waters. (Some entities use the terms Stormwater Control Measure, Stormwater Control, or Management Practice, but BMP is used in this manual for consistency with the International Stormwater BMP Database.) BMPs include both LID and non-lid practices, BMP System A BMP system includes the BMP and any related bypass or overflow. For example, the efficiency (see below) can be determined for an offline retention pond either by itself (as a BMP) or for the BMP system (BMP including bypass). Low Impact Development Low Impact Development (LID) is an overall land planning and engineering design approach to managing stormwater runoff. LID emphasizes conservation and use of on-site natural features to protect water quality. This approach implements engineered small-scale hydrologic controls to mimic the pre-development hydrologic regime of watersheds through infiltrating, filtering, storing, evaporating, and detaining runoff close to its source. LID is similar to Sustainable Urban Drainage Systems (SUDS), a term used in the United Kingdom, and Water Sensitive Urban Design (WSUD), a term used in Australia. The term Green Infrastructure may also be used, particularly in areas with combined sewer overflow (CSO) issues. LID Practice Individual practices used as part of overall LID developments or integrated into traditional developments include practices such as bioretention facilities, rain gardens, vegetated rooftops, rain barrels, permeable pavements and other infiltration-oriented practices. In some cases, LID terminology and traditional BMP terminology vary for the same basic practice. For example, the LID term bioretention may also be called porous landscape detention; the LID term bioswale may also be called grass swale. Performance measure of how well a BMP meets its goals for stormwater that the BMP is designed to treat. Effectiveness measure of how well a BMP system meets its goals in relation to all stormwater flows. Efficiency measure of how well a BMP or BMP system removes or controls pollutants. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-8

23 Introduction 1.4 Stormwater BMP Monitoring Purposes of BMP monitoring vary significantly and the monitoring program must be designed in the context of the objectives of the program. For example, a monitoring program for an industry seeking to comply with monitoring requirements under its National Pollutant Discharge Elimination System (NPDES) permit may be relatively straight-forward, whereas more in-depth monitoring research related to factors affecting BMP performance will be more complex. Key principles include: Dedicate the time and resources to develop a sound monitoring plan. Complexities of plans will vary depending on monitoring objectives. Be sure to plan and budget for an adequate number of samples to enable proper data interpretation. Be aware of the many static and state variables that need to be documented as part of a monitoring program. Exhibit 1-4 provides a brief overview of some key variables. Be sure that the monitoring design properly identifies the relationship between storm characteristics and the design basis of the BMP. (For example, is the intent of the monitoring program to assess performance over all storm conditions or only design conditions? What types of storms are considered to be adequately representative for purposes of monitoring?) Properly implement and follow the monitoring plan, clearly documenting any adjustments to the program. Particularly important are proper equipment installation and calibration, proper sample collection techniques and analysis, and maintenance of equipment for longer term programs. Expect the unexpected: rodents building nests in monitoring equipment, vandalism, battery/power failures, etc. Monitoring programs require attention and ongoing adjustment. Maintain data in an organized and well-documented manner, including not only monitoring data, but also BMP design and maintenance practices and site characteristics. Clearly report study limitations and other caveats on use of the data. The remainder of this Manual provides detailed guidance on many of these issues. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-9

24 Introduction Exhibit 1-4. Examples of Static and State Variables to Report in BMP Monitoring Programs (See Appendix A for a complete list specified by BMP type in the BMP Database.) Example Static Variables Tributary watershed conditions: Geographical location Watershed size and slope Land use type and characteristics (e.g., curb/gutter, imperviousness) Vegetative canopy/condition (may also be a state variable) Soil types and condition BMP design (e.g., length, width, height, storage volume, outlet design, upstream bypass, model number, etc.) Rainfall intensity Storm Size Flow rate Season Example State Variables Upstream non-structural controls Inter-event timing Settings for control structures such as gates, valves, and pumps Modifications to BMP design over time Maintenance of the BMP 1.5 The International Stormwater BMP Database As noted earlier in this chapter, a primary driver for the development of this Manual is the BMP Database project, which began in 1996 with the long-term goal of gathering transferable technical design and performance information to improve BMP selection and design so that local stormwater problems can be effectively addressed. In 2004, the project transitioned from a USEPA funded grant project to a more broadly supported coalition of partners including the Water Environment Research Foundation (WERF), ASCE Environmental and Water Resources Institute (EWRI), Federal Highway Administration (FHWA) and the American Public Works Association (APWA). These entities continue to provide long-term support of the project. The cornerstones of the project are the BMP monitoring and reporting protocols and the BMP Database itself, which were developed based on the input and intensive review of many experts for the purpose of developing standardized reporting parameters necessary for more accurate BMP performance analysis. The database encompasses a broad range of parameters including test site location, watershed characteristics, climate data, BMP design and layout characteristics, monitoring instrumentation, and monitoring data for precipitation, flow and water quality. The database is available for download from the project website ( and has evolved from its original 1999 release on CD to a more flexible and user-friendly structure. The three key component of the BMP Database include: 1) Data Entry Spreadsheets: These are forms for use by researchers and data providers to track BMP monitoring data, both for their own purposes, as well as for submitting data to the BMP Database. These spreadsheets are consistent with the structure and data elements contained in the original database release on CD, but allow more flexibility for database users in a familiar Excel format. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-10

25 Introduction 2) BMP Database: This is the master database itself, which is loaded with over 350 BMP studies and continues to grow through submission of studies from researchers and many entities regulated under the stormwater NPDES program. 3) BMP Performance Summaries: Data submitted to the database are analyzed on approximately an annual basis, with results reported in several different formats. Cumulative performance across BMP categories is provided in summary tables and brief reports, as well as in flat file spreadsheets containing a summary of analysis data. Additionally, BMP performance results for individual submitted studies in PDF format can be downloaded using the on-line search engine at Following the guidance provided in this Manual should typically result in studies being compatible for inclusion in the BMP Database and facilitate progress towards the BMP Database project s long-term goals, both with regard to traditional stormwater BMPs and LID approaches. 1.6 Regulatory Environment Although BMP monitoring is conducted for both regulatory and non-regulatory purposes, in many cases, it is driven by regulations, even if the regulation itself does not require monitoring. As general background for BMP monitoring, it is important to be aware of several key regulatory drivers related to BMP monitoring programs, including: The Clean Water Act (CWA) of 1972: Section 208 of 1972 CWA requires every state to establish effective BMPs to control nonpoint source pollution. The 1987 Water Quality Act (WQA) added Section 402(p) to the CWA, which requires that urban and industrial stormwater be controlled through the NPDES permit program. As a result, urban areas must meet requirements of Municipal Separate Storm Sewer System (MS4) permits, and many industries and institutions such as state departments of transportation must also meet NPDES stormwater permit requirements. Even if monitoring is not required under the NPDES permit, operators of regulated MS4s are required to develop a Stormwater Management Plan (SWMP) that includes measurable goals and to implement needed stormwater management controls (BMPs). MS4s are also required to assess controls and the effectiveness of their stormwater programs and reduce the discharge of pollutants to the maximum extent practicable. Section 303(d) of WQA requires the states to list those water bodies that are not attaining water quality standards including designated uses and identify relative priorities among the impaired water bodies. States must also develop Total Maximum Daily Loads (TMDLs) to assign allowable pollutant loads to various sources to enable the waterbody to attain designated uses in the future. (For more information about the TMDL program, see Implementation plans to achieve the loads specified under TMDLs commonly rely on BMPs to reduce pollutant loads associated with stormwater sources. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-11

26 Introduction Coastal Zone Act Reauthorization Amendments (CZARA) of 1990: CZARA was passed to help address nonpoint source pollution in coastal waters. Each state with an approved coastal zone management program must develop and submit to the USEPA and National Oceanic and Atmospheric Administration (NOAA) a Coastal Nonpoint Pollution Control Program (CNPCP), which provides for the implementation of the most economically achievable management measures and BMPs to control the addition of pollutants to coastal waters. CZARA does not specifically require that states monitor implementation of management measures and BMPs. They must, however, provide technical assistance to local governments and the public in the implementation of the management measures and BMPs, which may include assistance to predict and assess the effectiveness of such measures. CZARA also states that the EPA and NOAA shall provide technical assistance to the states in developing and implementing the CNPCP, including methods to predict and assess the effects of coastal land use management measures on coastal water quality and designated uses. The National Environmental Policy Act (NEPA): The National Environmental Policy Act (NEPA) establishes judicially enforceable obligations that require all federal agencies to identify the environmental impacts of their planned activities. The NEPA legislation and its requirements provide the framework under which environmental impacts of all substantial federal projects are evaluated, and have been the starting point from which many other environmental regulations are applied and enforced. Any major effort that involves federal funding, oversight, or permits, such as highway operations and projects, is subject to the NEPA process to ensure environmental concerns are considered and documented in an Environmental Impact Statement (EIS) before implementation. The Endangered Species Act: The Endangered Species Act of 1973 protects animal and plant species currently in danger of extinction (endangered) and those that may become endangered in the foreseeable future (threatened). It provides for the conservation of ecosystems upon which threatened and endangered species of fish, wildlife, and plants depend, both through federal action and by encouraging the establishment of state programs. State, Regional and Local Regulations: Increasingly, state and local governments and regional agencies may also develop their own rules and regulations requiring BMPs to protect drinking water supplies, recreational values, aquatic life and other beneficial uses. In some cases, such regulations focus primarily on water quality; however, more recently, such ordinances also focus on volume reduction through implementation of LID strategies that seek to mimic pre-development hydrology. Because regulations are continually evolving and may vary by location, it is always prudent to check with key federal, state, regional, and local sources for the most up-to-date regulatory requirements that could affect BMP monitoring programs. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-12

27 Introduction 1.7 Manual Scope Limitations The audience for this Manual is targeted primarily to those who possess a basic level of knowledge regarding stormwater quality, hydrology, and regulatory issues. The EPA website ( and other state and local websites can be referenced for additional guidance and background information. This Manual focuses primarily on the collection, reporting, and analysis of water quantity and quality measurements at the heart of quantitative BMP efficiency projects. It does not address, in detail, sediment sampling methods and techniques, biological assessment, monitoring of receiving waters, monitoring of groundwater, streambank erosion, channel instability, channel morphology, or other activities that in many circumstances may be as, or more, useful for measuring and monitoring water quality for assessing BMP efficiency. This Manual addresses methods that were in use at the time it was written. As the state of the practice and the design of monitoring equipment progress, new monitoring approaches and techniques, more sensitive devices, and equipment based on new technologies will likely be employed. Although the technology may change somewhat from that described herein, most of the basic flow and water quality monitoring methods discussed in this document have a long history of use and will most likely remain viable even as new and different technologies emerge. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-13

28 Introduction Exhibit 1-5. Other Resources for More Information on Stormwater Monitoring Burton and Pitt Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers. Lewis Publishers. California Stormwater Quality Association [CASQA] Municipal Stormwater Program Effectiveness Assessment Guidance. Caltrans Caltrans Comprehensive Monitoring Protocols Guidance Manual. CTSW- RT Center for Watershed Protection Monitoring to Demonstrate Environmental Results: Guidance to Develop Local Stormwater Monitoring Studies Using Six Example Designs. EPA NPDES Stormwater Sampling Guidance Document. EPA 833-B EPA EPA Monitoring Guidance for Determining the Effectiveness of Nonpoint Source Controls. EPA 841-B Granato et al National Highway Runoff Water-Quality Data and Methodology Synthesis, Volume I --Technical Issues for Monitoring Highway Runoff and Urban Stormwater. U.S. Department of Transportation, Federal Highway Administration. FHWA- EP p. Keith, L.H. ed Principles of Environmental Sampling, 2nd ed. American Chemical Society. National Research Council Urban Stormwater Management in the United States. National Academies Press. Oregon State University et al Evaluation of Best Management Practices for Highway Runoff Control, NCHRP-565. Transportation Research Board. Shaver et al Fundamentals of Urban Runoff Management: Technical and Institutional Issues, 2 nd Ed. USEPA and NALMS. State Water Resources Control Board and the Southern California Stormwater Monitoring Coalition Southern California Coastal Water Research Project, Model Monitoring Program for Municipal Separate Storm Sewer Systems in Southern California. Technical Report #419. ftp://ftp.sccwrp.org/pub/download/documents/technicalreports/419_smc_mm.pdf USDA-NRCS National Handbook of Water Quality Monitoring. 450-vi-NHWQM. Villanova Urban Stormwater Partnership Quality Management Plan and Quality Assurance Project Plans. QAPP.htm Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-14

29 Introduction 1.8 References Burton, A. and R. Pitt Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers. Lewis Publishers. California Stormwater Quality Association [CASQA] Municipal Stormwater Program Effectiveness Assessment Guidance. Caltrans Caltrans Comprehensive Monitoring Protocols Guidance Manual. CTSW- RT Center for Watershed Protection Monitoring to Demonstrate Environmental Results: Guidance to Develop Local Stormwater Monitoring Studies Using Six Example Designs. Driscoll, E.D., P.E. Shelly, and E.W. Strecker Pollutant Loadings and Impacts from Stormwater Runoff, Volume III: Analytical Investigation and Research Report. Federal Highway Administration Final Report, FHWA-RD p. Granato, G.E., Zenone, C., and Cazenas, P.A. (eds.), National Highway Runoff Water- Quality Data and Methodology Synthesis, Volume I --Technical issues for monitoring highway runoff and urban stormwater. U.S. Department of Transportation, Federal Highway Administration. FHWA-EP p. Keith, L.H. ed Principles of Environmental Sampling, 2nd ed. American Chemical Society. National Research Council Urban Stormwater Management in the United States. National Academies Press. Oregon State University, Geosyntec Consultants, University of Florida and Low Impact Development Center Evaluation of Best Management Practices for Highway Runoff Control, NCHRP-565. Transportation Research Board. Pitt, R., Maestre, A. and R. Morquecho The National Stormwater Quality Database (NSQD, Version 1.1) Shaver, E. Horner, R., Skupien, J., May, C. and G. Ridley Fundamentals of Urban Runoff Management: Technical and Institutional Issues, 2 nd Ed. USEPA and NALMS. State Water Resources Control Board and the Southern California Stormwater Monitoring Coalition Southern California Coastal Water Research Project, Model Monitoring Program for Municipal Separate Storm Sewer Systems in Southern California. Technical Report #419. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-15

30 Introduction ftp://ftp.sccwrp.org/pub/download/documents/technicalreports/419_smc_mm.p df U.S. Department of Agriculture Natural Resources Conservation Service (USDA-NRCS) National Handbook of Water Quality Monitoring. 450-vi-NHWQM. U.S. Environmental Protection Agency (EPA) Results of the Nationwide Urban Runoff Program, Volume I Final Report. U.S. Environmental Protection Agency, Water Planning Division, Washington D.C. U.S. Environmental Protection Agency NPDES Stormwater Sampling Guidance Document. EPA 833-B U.S. Environmental Protection Agency EPA Monitoring Guidance for Determining the Effectiveness of Nonpoint Source Controls. EPA 841-B U.S. Environmental Protection Agency Guidance for Quality Assurance Project Plans. EPA QA/G-5, USEPA, Office of Environmental Information, Washington, D.C. Villanova Urban Stormwater Partnership Quality Management Plan and Quality Assurance Project Plans. QAPP/WRLT-QAPP.htm Water Environment Research Foundation (WERF) Critical Assessment of Stormwater Treatment and Control Selection Issues. 02-SW-1. Urban Stormwater BMP Performance Monitoring Manual Chapter 1 June 2009 Page 1-16

31 Chapter 2 DEVELOPING A MONITORING PLAN This chapter provides a seven-step approach for developing a monitoring plan for collection of data to evaluate BMP effectiveness. The method described incorporates many elements that are included in EPA guidance regarding Data Quality Objectives (DQOs) (EPA 2006) and Quality Assurance Project Plans (QAPPs) (EPA 2002). Exhibit 2-1 provides a flow chart for working through these systematic steps, including the following: 1) Define Study Objectives 2) Identify Study Goals 3) Identify Information Inputs/Data Needs 4) Define Study Boundaries 5) Develop the Analytical Approach 6) Specify Performance or Acceptance Criteria 7) Develop Detailed Plan of Obtaining Data 8) Assess Reasonableness of Plan and Refine This chapter describes representative considerations for each of these steps in the context of stormwater BMP monitoring. Urban Stormwater BMP Performance Monitoring Manual Chapter 2 June 2009 Page 2-1

32 Developing a Monitoring Plan Exhibit 2-1. Systematic Approach to BMP Monitoring Plan Development (EPA 2006) Step 8. Assess Reasonableness and Refine Plan Urban Stormwater BMP Performance Monitoring Manual Chapter 2 June 2009 Page 2-2

33 Developing a Monitoring Plan 2.1 Step 1. Define Study Objectives/State the Problem It is very important that the objectives of a BMP monitoring program be clearly stated and recorded. The process of writing them down, working as a project team, generally results in careful consideration being given to the various possible objectives and questions to be answered. Written objectives help avoid misunderstandings by project participants, are an effective way of communicating with sponsors, and provide assurance that the monitoring program has been systematically planned. Studies of BMP performance are usually conducted to obtain information regarding one or more of the following questions: What degree of pollution control or effluent quality does the BMP provide under normal conditions (i.e., representative storm types)? How does hydrology for developed conditions compare with pre-development hydrology in terms of peak flow rates, runoff volume, peak timing, site infiltration capacity, etc.? How does this performance vary from pollutant to pollutant? How does this normal performance vary with large or small storm events? How does this normal performance vary with rainfall intensity? How do BMP design variables affect performance? How does performance vary with different operational and/or maintenance approaches? Does performance improve, decay, or remain stable over time? Does performance vary seasonally? (For example, to what extent is infiltration reduced during cold temperatures?) How does this BMP's performance compare with the performance of other BMPs? Does this BMP help achieve compliance with water quality standards? Many BMP monitoring programs have been established to satisfy requirements prescribed by permits to monitor the effectiveness of BMPs, but often the wording of such requirements is vague. Local program-specific objectives are likely to provide the soundest basis for planning a BMP monitoring study Key Activities for Step 1 Key activities for establishing monitoring objectives include the following: Urban Stormwater BMP Performance Monitoring Manual Chapter 2 June 2009 Page 2-3

34 Developing a Monitoring Plan 1) Identify project team and identify decision makers, including project management/oversight, field staff, office staff, analytical technicians or laboratory, data users, project advisors, and peer reviewers. 2) Describe the problem and develop a conceptual model of the BMP to be investigated and identify general types of data that will be collected (i.e. hydrology, water quality, physical characteristics of facility). As part of this step, it is also important to understand and document basic site conditions affecting monitoring. For example, what is the source of the runoff (e.g., roofs, pavements) and where are the collection pipes? In general, what pollutants are anticipated from each source? For example, roof runoff may have copper from downspouts, pavement may have elevated chlorides from road salting in the winter, and lawns may have bacteria loading from geese or dogs. Are there unique soil conditions or karst topography? Exhibit 2-2 provides an example conceptual model of a bioretention cell and data that could potentially be collected including surface inflows; overflows/bypass; underdrain outflows; evapotranspiration; precipitation; infiltration to underlying water table; soil characteristics such as porosity, hydraulic conductivity, and ph; water quality constituent inflows, outflows, storage and bypass; and transport mechanisms including vegetative uptake, sorption/desorption, and advective transport. As Exhibit 2-2 illustrates, in many cases the conceptual model developed as a part of Step 1 will have many parameters, often more parameters than it will be feasible to measure. Exhibit 2-2a. Conceptual Model for a Bioretention Cell with Underdrain (Source: Hunt 2003) (diagram terms defined in Exhibit 2-2b) Urban Stormwater BMP Performance Monitoring Manual Chapter 2 June 2009 Page 2-4

35 Developing a Monitoring Plan Exhibit 2-2b. Description of Conceptual Model Parameters (Source: Hunt 2003) 3) When a complex conceptual plan with many parameters is developed, it is necessary to make an assessment of the level of complexity of the monitoring that will be conducted. As a part of Step 1, parameters in the conceptual model can be prioritized into tiers that will aid in further steps to determine which parameters will be monitored, which ones will not be, and which ones will be estimated or calculated. 4) Discuss and evaluate alternative approaches to evaluating problem. Can goals be accomplished by evaluating data that have already been collected for other projects? If additional data are collected, can they be complemented by already-collected data? Because of the typically high cost of BMP monitoring, it may be desirable to evaluate alternative means for addressing some information needs (assuming that BMP monitoring Urban Stormwater BMP Performance Monitoring Manual Chapter 2 June 2009 Page 2-5