Wastewater Treatment Facilities Plan City of Wenatchee, Washington

Transcription

1 Wastewater Treatment Facilities Plan City of Wenatchee, Washington 210 North Worthen Street Wenatchee, WA Contact: Steve Brewer (509) Prepared for City of Wenatchee November 2008 Prepared by

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3 Contents 1.0 Summary, Conclusions, and Recommendations Summary Conclusions Recommendations Introduction Description of Discharge Standards Summary of Water Quality Standards National Pollutant Discharge Elimination System Permit Requirements Biosolids Reclassification Background Information Existing Environment Climate Geology and Soils Surface Water Resources Sensitive Areas Endangered and Threatened Species Public Health Prime or Unique Farmland Archaeological and Historical Sites Federally Recognized Wild and Scenic Rivers Existing Wastewater Flows and Wasteloads Population and Land Use Flows and Wasteloads Determination of Excessive Infiltration/Inflow Capacity of Existing WWTP Pro2D Calibration Activated Sludge Process Capacity Future Conditions Population and Land Use Forecasted Flow and Wasteloads Water Conservation and Flow Reduction Future Industrial Wastewater Forecasted Flow and Wasteloads Future Environment Without Project Capacity Visual Environment Odor Control Effluent Discharge Page iii

4 CONTENTS 6.0 Alternatives Improvements to Existing WWTP Expansion of the Activated Sludge Process Anaerobic Digestion Improvements Drying Bed Expansion Visual Aesthetic Improvements Odor Control Improvements Reclaimed Water Facilities Miscellaneous Maintenance Improvements Cost Estimates for Evaluated Facilities Cost Estimate for New WWTP Evaluation of Alternatives and Conceptual Design Drying Bed Improvements Influent Pump Station Existing Influent Pump and Configuration Replacement Pump Requirements Pumping System Modifications Required Replacement Pump Installation Financial Analysis Other Water Quality Management Plan Conformance SEPA Environmental Checklist SERP Compliance List of Required Permits References Appendixes A B C D E Toxic Substances Criteria NPDES Waste Discharge Permit No. WA Pro2D Model Output WWTP and Preliminary Design of Sludge Drying Beds and Raw Sewage Pumps Improvements Information SEPA Environmental Checklist Tables 1-1 Estimated Cost of Improvements Used to Calculate Residential Rate Impacts Aquatic Life Use Criteria Wenatchee WWTP Effluent Limits Land Use Inventory Existing Wastewater Flows and Wasteloads Calibration of Pro2D Model for Wenatchee WWTP Comparison of Population Served, Wastewater Flow, BOD, and TSS for WWTP in 1980 and iv

5 CONTENTS 4-5 Estimates of BOD and TSS When Average Annual Flow Reaches 5 mgd Users Connected to Wenatchee WWTP Summary of Flow, BOD 5 and TSS Projections for City of Wenatchee WWTP Forecasted Flow and Wasteloads Summary of Improvement Cost Estimates Aggregate Bituminous Surface Course Drying Bed Expansion Design Criteria Existing Raw Sewage Pumps No. 1 and No. 2 Data Existing Raw Sewage Pumps No. 1 and No. 2 Performance Criteria Estimated Costs of Improvements Used to Calculate Residential Rate Impacts Figures 2-1 Facilities Planning Area, City of Wenatchee Effluent CBOD Effluent TSS Effluent Ammonia Effluent Fecal Coliform Location of Existing Drying Beds Activated Sludge Capacity Project Schedule for Maximum Grant and Loan Funding Potential Improvements, Wenatchee WWTP Construction Cost Estimate Accuracy Ranges Sludge Drying Beds Expansion Demolition Plan Sludge Drying Beds Expansion Construction Plan Influent Pump Station Raw Sewage Pump Replacement Plans and Section v

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7 CHAPTER 1 Summary, Conclusions, and Recommendations This Wastewater Treatment Facilities Plan has been prepared to satisfy the requirements established in Washington State Department of Ecology (Ecology) Consent Order DE 02QCR The primary purposes of this plan are as follows: 1. Show that adequate capacity exists to treat estimated flow for the next 10 years 2. Estimate the cost of possible improvements to provide capacity for future wastewater flows after the current wastewater treatment plant (WWTP) capacity is fully used. The planning period for this plan is 2005 to Summary The recently improved WWTP has a maximum capacity for an annual average flow of 5.0 mgd (million gallons per day) based on the wastewater characteristics projected for a 2025 service population of 43,526. Assuming that the population growth rate continues at the rate projected for the time period, the maximum capacity of the WWTP will be reached in approximately There are many assumptions that must be made to make this prediction, and the date that WWTP capacity is reached could be earlier or later than estimated. The minimum capacity is estimated to be 4 mgd, estimated to be reached in Decisions to construct improvements need to occur several years prior to facilities reaching capacity because of the long lead time for financing, design, bidding, and construction. A minimum of 3 years is needed if the City requires no outside financial assistance. A minimum of 7 years is needed if the City desires to obtain State Revolving Fund (SRF) loan funds for planning, design, and construction. Expansion of the WWTP greater than the current design capacity of 5 mgd of wastewater will require additional activated sludge and solids handling facilities. These facilities are assumed to be constructed in 2025 for purposes of estimating the rate impacts. By 2010 two improvements are needed to expand the capacity of existing facilities. First, mixing and heating improvements are needed for the existing secondary anaerobic digester to allow it to operate as a backup to the two existing primary digesters. This increases the rated capacity of the existing anaerobic digesters 100 percent. Second, the sludge drying beds are at capacity in wet weather and additional capacity is needed. A sludge management plan is needed to address Ecology regulation changes in the way that the biosolids that Wenatchee produces are classified. A recent change in regulation reclassifies the biosolids from Class A to Class B. The City needs to study the impacts of the changed regulation on how the City manages biosolids and the type of solids processes that will be needed in the future. City staff is currently working with the farmer who has historically accepted Wenatchee biosolids and with County and Ecology regulatory agencies to obtain the required permits for land application of Class B biosolids. 1-1

8 The City is planning for improvements to reduce WWTP maintenance and enhance the WWTP as a neighbor. These improvements do not increase the WWTP capacity or improve effluent quality. These improvements can be made at the City s discretion and are not required by Ecology. New influent pumps can be installed to eliminate the need to remove rags from the impellers on a daily basis. New fine screens with washer-compactors can be installed to eliminate primary sludge pump plugging. Visual mitigation and odor control are proposed to improve the appearance of the WWTP and to control odors from the facility. Costs for visual mitigation and odor control approaches selected by City staff are modest. Visual mitigation and odor control studies are recommended to identify the approaches suitable for Wenatchee and to develop more accurate cost estimates for these improvements. Costs for effluent filtration facilities are included to allow the City to develop facilities to reuse 1.0 mgd of effluent for irrigation or other suitable use of Class A reclaimed water. Table 1-1 summarizes the estimated costs and approximate year the improvements are needed. The costs are in January 2007 dollars. The cost estimates are Class 5 estimates as defined by the American Association of the Advancement of Cost Engineering International with an accuracy of +100 to -50 percent of actual costs. The costs are total project costs and include Washington State sales tax and an allowance for engineering, legal, and administration. These costs have a low level of accuracy because the level of project definition and engineering is low. City staff requested that the facilities plan estimate the costs of possible improvements using representative improvements rather than evaluate alternatives because the need for the improvements was many years from now and technology would change, thus making the evaluations outdated before they were implemented. As a result, except for sludge drying bed and raw sewage pumps, this facility plan does not evaluate alternatives or present a conceptual design of recommended improvements to satisfy WAC for engineering reports. To satisfy WAC , this facility plan would be amended with specific evaluations of alternatives and conceptual designs prior to proceeding with improvements to the WWTP. TABLE 1-1 Estimated Cost of Improvements Used to Calculate Residential Rate Impacts Improvement New influent pumps $240,000 New fine screens $1,300,000 Expansion of activated sludge process $17,000,000 Anaerobic digestion Heating and mixing of secondary digester $740,000 Future primary digester $5,100,000 Drying bed expansion $1,100,000 Visual aesthetic improvements $3,600,000 Odor control improvements $4,200,000 Reclaimed water facilities (1.0 mgd) $2,700,000 Sludge management plan $150,000 Visual mitigation study $200,000 Odor control plan $100,

9 TABLE 1-1 Estimated Cost of Improvements Used to Calculate Residential Rate Impacts Improvement Total Capital Costs $14,330,000 $22,100,000 Increased Annual O&M Expansion of activated sludge process $320,000 Anaerobic digestion Future primary digester $53,000 Increased Annual O&M Costs $0 $373,000 All costs expressed in January 2007 dollars. The rate increases for residential customers to pay for the improvements shown in Table 1-1 depend on the method of financing. The improvements are assumed to be constructed in either 2010 or Using 20-year revenue bonds with 50-percent coverage, the rate increase is projected to be $9.58 per month in 2010 and increase to $26.43 per month in Using SRF loans for all expenses, the rate increase is projected to be $5.40 per month in 2010 and increase to $15.80 per month in Conclusions The existing activated sludge and anaerobic digestion processes control the capacity of the WWTP to accept additional service population. The WWTP has 11 mgd peak flow capacity, and with use of the flow equalization basin located on the other side of Worthen Street, has adequate hydraulic capacity. There is space on the existing WWTP site to add an additional anaerobic digester to add capacity to approximately 7 mgd. Additional anaerobic digester capacity could be provided if a taller digester design is used. The existing activated sludge process has a maximum average annual capacity of 5 mgd when operated in the step-feed mode. Space is available on the existing WWTP site to add a parallel 1 mgd of annual average capacity using a membrane bioreactor (MBR) type of process. The addition of the anaerobic digester, the parallel 1-mgd MBR facility, and water reclamation facilities completely fill the existing WWTP site. This would increase the capacity to 6 mgd average annual flow. The cost of a new 8-mgd WWTP located within 5.5 miles of the existing WWTP is estimated to be approximately $160 million. The City decided, for now, that it will expand the WWTP on a site it owns across Worthen Street to the west of the existing WWTP site. Potentially, another 4 mgd average annual of MBR facilities could be located on this site which could increase the maximum average annual flow capacity of the existing WWTP site to 10 mgd. 1.3 Recommendations 1. City investigate and confirm the accuracy of flow measurement and sampling with particular attention to waste activated sludge (WAS) and influent and primary effluent biochemical oxygen demand (BOD) and total suspended solids (TSS). WEN_FAC_PLAN_11_17_08.DOC 1-3

10 2. City review influent waste loads annually to confirm loading increases are within planning assumptions. 3. Preparation of facilities plan amendments for WWTP improvements that evaluate alternatives and include conceptual designs and obtain Ecology approval prior to proceeding with improvements. 4. Preparation of an odor control plan to determine the odor control facilities appropriate to Wenatchee and their cost. 5. Preparation of visual mitigation plan to determine visual mitigation facilities appropriate to Wenatchee and their cost. 6. Anaerobically digest primary and thickened waste activated sludge (TWAS) together in the two existing primary digesters. 7. Recommend modifying the overflow piping to allow operation of Primary Digester No. 2 at the increased elevation of Preparation of a sludge management plan that evaluates biosolids management alternatives and solids processing prior to making solids improvements. 9. Use of Hidrostal influent pumps to eliminate ragging problems. 10. Use of 1/4-inch-diameter-opening perforated plate escalator screens and washer compactors to eliminate primary sludge pump plugging. 1-4

11 CHAPTER 2 Introduction This Wastewater Treatment Facilities Plan (Facilities Plan), City of Wenatchee, Washington, has been prepared to satisfy the requirements established in Washington State Department of Ecology (Ecology) Consent Order DE 02WQCR The primary purpose of the Facilities Plan is to show that adequate WWTP capacity exists for the next 10 years and develop a capital improvement program based on possible improvements needed to provide capacity for future wastewater flows. The planning period for the facilities plan is 2005 to The majority of improvements are not needed for another 10 years or more, and technology is likely to change in this time interval. As a result, City staff has requested that this plan estimate the costs of possible improvements using representative improvements rather than evaluate alternatives. Representative improvements are based on facilities that have been successfully used at one or more WWTPs to satisfy similar requirements in other jurisdictions. Costs for the representative improvements are based on the actual costs experienced, increased using general cost escalation factors, and adjusted using accepted scaling factors to the Wenatchee facilities. When the City decides to proceed with improvements to the WWTP, amendments to this Facilities Plan will be prepared that evaluate alternative approaches and develop design criteria for the potential improvements. Figure 2-1 shows the facilities planning area, which consists of the area within the current city limits of the City of Wenatchee, plus an unincorporated area in Chelan County north of the Wenatchee River referred to as the Sunnyslope area. The planning area is bounded by the Columbia River on the east and foothills to the west. The planning area is within the Wenatchee urban growth boundary established by Chelan County. The following information is provided in this Facilities Plan: The capacity of the existing WWTP was estimated and projections were made to estimate when this capacity will be reached. Costs for increasing the capacity of the existing WWTP were developed including: Adding secondary treatment capacity Improving the performance and capacity of the anaerobic digesters Expanding the existing sludge drying beds Improvements to the existing WWTP to improve visual aesthetics and reduce odors Additional treatment to allow use of the effluent on the Riverfront Park and for other irrigation purposes For purposes of comparison, rough estimates were prepared for constructing a new WWTP at another location. 2-1

12 A series of studies and WWTP improvements are recommended on a schedule to maintain WWTP capacity. This information provides the basis for a capital improvements program. 2-2

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15 CHAPTER 3 Description of Discharge Standards Facility planning for wastewater treatment plants (WWTPs) is based on the level of treatment required and the quantity of wastewater to be treated. This chapter examines current and potential future requirements for level of treatment. The WWTP discharges to the Columbia River, and the treatment level is determined by the water quality in this receiving stream. The Wenatchee River is also addressed because it passes through the northern end of the planning area and has the potential to be a future receiving water body. 3.1 Summary of Water Quality Standards This section summarizes the current and anticipated water quality standards for the Columbia River in the vicinity of the WWTP discharge point. Water quality standards can change as a result of water quality improvement projects or Total Maximum Daily Load (TMDL) studies conducted by Washington State Department of Ecology (Ecology) and the U.S. Environmental Protection Agency (EPA). Discharge requirements for the City of Wenatchee are not anticipated to change in the next 10 to 20 years because there are no nutrient or dissolved oxygen (DO) TMDLs active or planned for the Columbia River. There is a temperature TMDL currently on hold, although this is not likely to affect the Wenatchee WWTP discharge standards. However, growth is occurring along the Wenatchee River. TMDL studies are being conducted on the Wenatchee River for DDT and temperature. A DO, ph, and phosphorus TMDL study was published in April 2006 for the Wenatchee River, and a fecal coliform TMDL was completed in Based on these studies, the water quality standards for the Wenatchee River are likely to change and become much more stringent. These water quality standards could affect any new WWTP discharging to the Wenatchee River. Current water quality standards for the Columbia River are listed in the Washington Administration Code (WAC) A-200, which describes the water quality standards for all surface waters within the state. The standards for the Columbia River at the City of Wenatchee are summarized below. The Columbia River has an aquatic life use designation of salmon/trout spawning, noncore rearing, and migration. This classification determines aquatic life temperature, dissolved oxygen, turbidity, total dissolved gas, and ph criteria. These criteria are listed in Table 3-1. The Columbia River is also classified as Primary Contact Recreation. This classification requires that fecal coliform organism levels must not exceed a geometric mean value of 100 colonies/100 ml, with not more than 10 percent of all samples (or any single sample when less than 10 sample points exist) obtained for calculating the geometric mean value exceeding 200 colonies/100 ml. The Columbia River is listed as an appropriate water supply for domestic, agricultural, industrial, and stock watering uses as well as the miscellaneous uses of wildlife habitat, 3-1

16 harvesting, commerce and navigation, boating, and aesthetics. For these uses, Table A-1 in Appendix A details the criteria for toxic, radioactive, and deleterious materials. TABLE 3-1 Aquatic Life Use Criteria Parameter Aquatic life temperature Aquatic life dissolved oxygen (DO) Aquatic life turbidity criteria in fresh water Aquatic life total dissolved gas criteria in fresh water Aquatic life ph criteria in fresh water Criterion The highest 7-day average of the daily maximum temperatures (7-DADMax) is 17.5 Celsius (63.5 Fahrenheit). The lowest 1-day minimum is 8.0 mg/l. 5 NTU (Nephelometric Turbidity Unit) over background when the background is 50 NTU or less; or a 10 percent increase in turbidity when the background turbidity is more than 50 NTU. Total dissolved gas shall not exceed 110 percent of saturation at any point of sample collection. ph shall be within the range of 6.5 to 8.5, with a humancaused variation within the range of less than 0.5 units. 3.2 National Pollutant Discharge Elimination System Permit Requirements Effluent from the treatment plant is discharged into the Columbia River. To protect the water quality of the river, the effluent must meet treatment standards identified by Ecology. The plant's current National Pollutant Discharge Elimination System (NPDES) permit, issued in 2005, describes the discharge standards for the plant and is provided in Appendix A. Effluent limits for the plant are summarized in Table 3-2. The existing standards described in Section 3.1 are achieved by meeting the requirements of the NPDES permit as described in this section. The City is not requesting any changes to the effluent limits shown in Table 3-2 which are from the current NPDES permit. Figures 3-1 through 3-4 show effluent CBOD, TSS, total ammonia, and fecal coliform for September 2005 through September The most recent WWTP improvements began operation in September Effluent CBOD, TSS, fecal coliform, and total ammonia are much lower than the maximum permitted discharge concentrations. 3.3 Biosolids Reclassification Ecology revised biosolids regulations for the State of Washington that eliminated Alternative 4 of CFR503 for achieving Class A biosolids in the sludge drying beds. The biosolids from the drying beds will now be classified as Class B and be subject to different regulatory requirements. The City is working with the farmer who has historically accepted Wenatchee biosolids and with County and Ecology personnel to obtain permits and regulatory approvals required to land-apply Class B biosolids. 3-2

17 TABLE 3-2 Wenatchee WWTP Effluent Limits Parameter Average Monthly Average Weekly 5-Day Carbonaceous Biochemical Oxygen Demand (CBOD 5) Total Suspended Solids (TSS) 25 mg/l; 1,147 lb/day 85% removal of influent CBOD 5 30 mg/l, 1,376 lb/day 85% removal of influent TSS 40 mg/l; 1,835 lb/day 45 mg/l, 2,064 lb/day Fecal Coliform Bacteria 200/100 ml 400/100 ml ph Daily minimum is equal to or greater than 6.0 and the daily maximum is less than or equal to 9.0. Parameter Average Monthly Maximum Daily a Total Ammonia (as NH 3-N) 25 mg/l; 1,147 lb/day 47 mg/l; 2,156 lb/day Note: The average monthly and weekly effluent limitations are based on the arithmetic mean of the samples taken with the exception of fecal coliform, which is based on the geometric mean. a The maximum daily effluent limitation is defined as the highest allowable daily discharge. The daily discharge means the discharge of a pollutant measured during a calendar day. For pollutants with limitations expressed in units of mass, the daily discharge is calculated as the total mass of the pollutant discharged over the day. 3-3

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23 CHAPTER 4 Background Information This chapter establishes the existing wastewater flows and wasteloads being treated by the Wenatchee WWTP and determines the capacity of the WWTP in its current configuration. The flows and wasteloads are based on the existing environment, the population and land use in the service area, and infiltration and inflow to the collection system. The existing flows, wasteloads, and plant capacity are used in Chapter 5 to determine future wastewater flows and wasteloads and estimate future facility requirements. 4.1 Existing Environment The City of Wenatchee is located in central Washington on the east side of the Cascade Mountain Range. The City lies in the Columbia River Valley, just south of the confluence of the Wenatchee and Columbia Rivers. The Columbia River forms much of the eastern boundary of the Wenatchee city limits Climate The climate of the area is heavily influenced by the Cascade Mountain Range. The prevailing westerly flow of air across the Cascades loses much of its moisture before reaching the Wenatchee area. The result is a relatively dry and mild climate pattern. The area experiences average precipitation of around 9 inches, with snowfall averaging 30 to 35 inches in the winter. Precipitation patterns are characterized by infrequent rainfalls of high intensity. Temperatures range from an average of 26 degrees Fahrenheit (ºF) in January to 73ºF in July Geology and Soils The major geologic formation underlying the area is the Wenatchee Formation. This formation is composed of medium- to course-grained sandstone that is cross-bedded with pebbly sandstone. Stream deposits (alluvium) consisting of uncemented silt, sand, or gravel overlie the Wenatchee Formation. Flooding during the Ice Age is thought to have deposited a layer of clay in the valley that has rendered much of the area unsuitable for septic tanks. Available City records and existing borings drilled at the existing wastewater treatment plant site in 1972 for a previous plant improvements project indicate that the site has been used as a solid waste disposal area. Refuse has not been accepted at the site since Much of the refuse was excavated and removed from the site during construction of the secondary clarifiers and aeration basins in 1975 and during construction in Additional refuse remains within the WWTP site and in areas surrounding the WWTP site. The WWTP site is greatly disturbed and soils at the site are not considered prime or unique soils. The soils existing at the site of the existing drying beds are PrB-Pogue gravelly fine sand loam, which is on the prime soils list, and PrC-Pogue gravelly fine sandy loam, which is on 4-1

24 the unique soils list. However, these are not considered prime or unique soils unless they are irrigated, which they are not. Figure 4-1 shows the location of the drying beds Surface Water Resources The Columbia and Wenatchee Rivers are two major surface water resources in the area. Both are regulated for hydroelectric power generation and irrigation supply. The effluent from the Wenatchee WWTP discharges into the Columbia River in an area where it is designated as a Class A water course by Ecology. Columbia River water quality in the Wenatchee area is generally quite good and influenced more by naturally occurring impurities gathered at times of high runoff than by human activities. To protect the water quality of the receiving water resource from contamination by elements in wastewater discharged by the WWTP, treatment standards must be met as specified in the NPDES permit issued for the plant (see Chapter 3). Reliability and redundancy in the treatment works are also specified in regulations to protect the water quality of surface water resources receiving treated effluent. The designation of Reliability Class II (as defined in Technical Bulletin Design Criteria for Mechanical, Electric, and Fluid System and Component Reliability by U.S. EPA issued 1974 and described in Table G2-6 of Criteria for Sewage Works Design by Ecology in December 1998) applies to works for which discharge or potential discharge as a result of volume and/or character would not permanently or unacceptably damage or affect the receiving waters or public health during periods of short-term operations interruptions, but could be damaging if continued interruption of normal operations were to occur (on the order of several days). Tables G2-7 and 8 of the Criteria contains specific requirements excerpted from the EPA technical bulletin. The Wenatchee treatment system is designated to meet requirements of Reliability Class II, which include works with a discharge or potential discharge moderately distant from shellfish areas, drinking water intakes, areas used for contact water sports, and residential areas. In accordance with the requirements of Reliability Class II, capabilities must be provided for satisfactory operation of the Wenatchee treatment works during power failures, flooding, peak loads, equipment failure, and maintenance shutdown Sensitive Areas Neither the existing WWTP site nor the existing drying bed site is located in a sensitive area. The WWTP and sludge drying beds are located at higher elevation than the 100-year-flood elevation and are not subject to flooding. Both sites do not contain and are not located adjacent to wetlands Endangered and Threatened Species The Washington Department of Fish and Wildlife (WDFW) has determined the Columbia River to be priority habitat for certain species of resident and anadromous fish. The upper Columbia River spring run of Chinook salmon and the upper Columbia River steelhead are listed as federal threatened species under the Endangered Species Act. WDFW also calls out the City of Wenatchee as being a part of the historical winter range for mule deer. This winter range has been lost due to agriculture, housing development, and game fences. The drying bed site has not yet been mapped by WDFW for priority habitats and/or species. 4-2

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27 4.1.6 Public Health The Chelan-Douglas Health District does not have a system for tracking failing septic tanks. However, according to the Health District, failing septic tanks have become a major issue for many jurisdictions in the area near Wenatchee. The Health District believes that it can be assumed that many of the older septic tanks in the area are failing or will fail in the near future. 1 The Health District believes that planning to expand capacity to allow those with failing septic tanks to connect to the sewer system would be beneficial in the long term for public health Prime or Unique Farmland There is no record of the WWTP site or the sludge drying bed site ever having been used as farmland. Available City records and existing borings drilled at the plant site in 1972 for a previous plant improvement project indicate that the site has been used as a solid waste disposal area. Refuse has not been accepted at the site since Much of the refuse was excavated and removed from the site during construction of the secondary clarifiers and aeration basins in Additional refuse remains within the WWTP site and in areas surrounding the site Archaeological and Historical Sites A field survey of the area in the vicinity of the drying bed site was conducted in January The survey found two separate archaeological sites located a distance away from the drying beds. One site contains 22 or more rock cairns. These cairns are suspected to be Native American burial sites. The other site has low-density lithic scatter. Petrified wood, cryptocrystalline (ccs) flakes, and a cryptocrystalline biface knife fragment were found at this site. Consultation with the Colville Federated Tribes and the Washington Department of Archaeology and Historic Preservation must be conducted before any work is performed in the area Federally Recognized Wild and Scenic Rivers Neither the Columbia River nor the Wenatchee River are federally recognized wild and scenic rivers. However, both rivers are important to the region because they provide habitat for threatened and endangered species. They also provide recreation for local residents and tourists. 4.2 Existing Wastewater Flows and Wasteloads This section describes the population and land use in the Wenatchee service area, the current wastewater flows and wasteloads being treated at the WWTP, and any excess infiltration and inflow included in the existing flows. 1 Septic tanks fail because the drainfield fails for a variety of reasons. This leads to sewage on the ground surface or groundwater contamination. Septic tanks can also cause elevated concentrations of nitrate and sometimes fecal coliform to build up in the groundwater. Failing septic tanks causing health problems due to ponding on the surface and groundwater contamination are the public health issues. 4-5

28 4.2.1 Population and Land Use Population The City s comprehensive plan (2006) provides the following information: With 29,920 residents [in 2006], Wenatchee is currently the 34th largest city in the state of Washington. Of all cities in Washington State, Wenatchee places 12th in terms of people per square mile. Wenatchee experienced strong growth in the 1990s. Between 1990 and 2000, Wenatchee s population grew 28 percent, similar to the growth rate of Chelan County (27 percent). Wenatchee s population represented 42 percent of the total county population during both census years. For wastewater facility planning, it is necessary to plan for the connected population, which is the population that is currently connected and is forecasted to be connected to the sewer system within a specified time period, and who send wastewater to the City treatment plant. There are still homes in Wenatchee that use on-site septic systems and are not connected to the sewer system. The City s sewer system serves the area within the city limits, plus a few areas outside of the city limits. In year 2006 the City had 8,278 residential sewer accounts, representing approximately 7,903 single family residences and 375 multifamily residences, with a total estimated population served of 29,240 persons. Of this, approximately 27,918 people are within the city limits, representing about 93 percent of the city s population. Outside the city limits, there were about 494 single family and 8 multi-family accounts representing about 1,322 people. There are estimated to be about 792 dwelling units (2,003 persons) on septic systems within the City limits, based on discussions with Chelan-Douglas Health District and the City, combined with review of the number of residential accounts and population estimates. The island of Chelan County land that is surrounded by city limits is almost entirely served by on-site septic systems and is not included in this number (they are outside city limits). The Sunnyslope Urban Growth Area (UGA), located north of the Wenatchee River, currently is located in unincorporated Chelan County and will be served by the City of Wenatchee WWTP. The Chelan County Draft Sunnyslope Subarea Plan (Studio Cascade 2007) lists a current estimated population of about 3,100 people for the Sunnyslope UGA. Currently, there are only three properties at Sunnyslope that are served with sewer: Sunnyslope Elementary School, the U.S. Forest Service building, and a car wash that is under construction Land Use The City of Wenatchee currently encompasses approximately 4,725 acres (City of Wenatchee, 2006). Within the city limits there is a mix of residential land use of varying densities, commercial uses, and warehouse industrial uses. Residential use dominates the land use in Wenatchee, more than 60 percent of the City. Slightly more than 10 percent of the urban area is used for commercial purposes (City of Wenatchee, 2006). Table 4-1 summarizes the land use for the city and the UGA south of the Wenatchee River. 4-6

29 TABLE 4-1 Land Use Inventory City of Wenatchee and Urban Growth Area South of the Wenatchee River Land Use Acres % of Total Civic and Cultural Commercial Industrial Multi-family Parks & Open Space Public Facilities Resource Lands Single Family 2, Undeveloped Source: Table 5 of City of Wenatchee (2006). TOTAL 5, The UGA outside the current city limits is zoned as mostly residential, with areas of commercial and industrial zoning. Within the city limits, there is an island of Chelan County land that has not been annexed into the City. The City and County entered into an interlocal cooperative agreement in 2004 that addresses the Olds Station and Sunnyslope areas. This agreement incorporated the Sunnyslope and Olds Station UGA into the City s UGA. The agreement leaves planning responsibilities for Sunnyslope/Olds Station with the County, but obligates the City to plan for and supply sanitary sewer service within the existing and any expanded Sunnyslope UGA. In November, 2005, the County commissioned a consultant to create the Sunnyslope Long-Range Plan. The City adopted a waterfront sub-area plan in The plan aims to encourage new development, both high-density residential and commercial, along the waterfront from about Chehalis Street on the south end to the Wenatchee River on the north end. This area will receive consideration in planning sanitary sewer and evaluating the impacts on the current system Flows and Wasteloads Wenatchee WWTP flow and wasteload data were analyzed for the years 2000 and 2001 to establish existing wastewater flows and wasteloads. These data are summarized in Table 4-2. Complete data analysis and a graphical presentation of the data are available in Appendix B of Final Facility Plan Amendment for Wenatchee Wastewater Treatment Plant Improvements (CH2M HILL, 2003). The draft Comprehensive Sewer Plan (City of Wenatchee, October 2008) shows influent data for the years 2002 through Data show 5 to 10 percent lower influent BOD and TSS in 2006 and 2007 compared to The City has emphasized control of fats, oil and grease (FOG) from commercial dischargers and 4-7

30 industrial pretreatment since 2002 and these programs along with changes in industrial dischargers may be affecting the amount of BOD and TSS discharged to the sewer system accounting for the observed reduction in BOD and TSS. TABLE 4-2 Existing Wastewater Flows and Wasteloads Plant Flow (mgd) Average annual Maximum 30-day Maximum 7-day Maximum day Peak hour Plant Influent BOD (lb/day) Average annual 6,324 7,003 Maximum 30-day 7,011 7,725 Maximum 7-day 7,656 8,833 Maximum day 9,438 13,532 TSS (lb/day) Average annual 6,984 7,465 Maximum 30-day 8,255 8,588 Maximum 7-day 9,462 10,159 Maximum day 13,544 13,631 Ammonia (lb/day) Average annual Maximum 30-day Maximum 7-day Maximum day Peak flow at the Wenatchee WWTP is different from the peak flow at many WWTPs. In 2005, a new equalization basin was installed west of Worthen Street to store peak flow in excess of 11 mgd. As Table 4-2 shows, peak flows to the Wenatchee WWTP can exceed 11 mgd for short periods of time. These high flows are associated with intense rainfall during thunderstorms or possibly snowmelt. The magnitude of extreme events is not known because they exceed the 15-mgd maximum range of the WWTP flowmeter. The equalization basin is sized to limit the maximum flow to the WWTP treatment processes to 4-8

31 11 mgd by storing flows above that level until the flows to the WWTP are less than that level, and then releasing the stored flow. The firm hydraulic capacity of the WWTP is 11 mgd, and the equalization basin is needed to prevent hydraulic overloading of the WWTP Determination of Excessive Infiltration/Inflow The draft 2008 Comprehensive Sewer Plan prepared by the City of Wenatchee found that infiltration and inflow (I/I) in the City s collection system are not excessive based on available data and U.S. EPA guidelines. The details of the I/I evaluation may be found in the Comprehensive Sewer Plan. 4.3 Capacity of Existing WWTP This section evaluates the capacity of the existing WWTP after completion of improvements in September The purpose of the capacity analysis is to provide an accurate estimate of the capacity of the WWTP using operating data obtained after completion of the improvements to the WWTP. The improvements included the following: Construction of flow equalization basin Replacement of influent gates Replacement of raw sewage pumps and drives for normal flows Replacement of coarse bubble diffused aeration diffusers with fine bubble diffusers in the aeration basins Installation of baffles in aeration basin to create four aeration zones in each aeration basin Installation of mixers in the first aeration zone and mixed liquor pumps in final aeration zone to allow operation of first aeration zone in anoxic conditions Modification of influent and effluent channels to allow operation of the activated sludge process in plug flow and step-feed modes Replacement of secondary clarifier mechanisms Modification of return activated sludge (RAS) pumping control Replacement of chlorine disinfection with ultraviolet disinfection Modification of WWTP stormwater piping to discharge onsite POTW stormwater into the influent pump station instead of Columbia River Change of control system for liquids treatment portion of WWTP to programmable logic controller and personal computer supervisory control and data acquisition (SCADA) systems The improvements to the aeration basins, activated sludge process, secondary clarifiers, and RAS pumping affect the capacity of the WWTP, but the other improvements have no effect 4-9

32 on WWTP capacity or maintain the 11-mgd firm hydraulic capacity of the WWTP. The capacity evaluation focused on the capacity of the activated sludge process, which consists of the aeration basins, aeration system, secondary clarifiers, and RAS pumping. The 11-mgd firm hydraulic capacity was established in the improvements completed in 1992, is not being changed, and therefore is not evaluated in this Facilities Plan. The capacity evaluation was done using Ecology s Criteria for Sewage Works Design (Ecology, 1998), and CH2M HILL s Pro2D wastewater process model. The Wenatchee WWTP is a Class II reliability facility as described earlier in this report, and the evaluation is based on the criteria for Class II reliability. All WWTPs in the state of Washington must comply with criteria in the Ecology manual. Ecology s Criteria for Sewage Works Design allows the use of modeling for evaluation of activated sludge processes. The Pro2D model was developed to calculate loading parameters to confirm conformance with Ecology criteria. It is a spreadsheet-based model that models the entire WWTP, and develops loading criteria for each unit process as well as detailed mass balances. Pro2D uses the ASM 2d model to calculate activated sludge operating parameters. An international group of experts developed the ASM 2d model, which is widely used for evaluation of activated sludge processes and meets the requirements for Criteria for Sewage Works Design. Appendix C contains summaries of the Pro2D modeling results used in this evaluation Pro2D Calibration The Pro2D model was calibrated using Wenatchee WWTP data. Data for July and August 2006 was used to calibrate the model for the summer when the wastewater is warmer. Calibration for the winter when the wastewater is colder was done for January The plant s biological process was modeled as plug-flow reactor of four stages with an initial 12 percent anoxic zone followed by three aerobic zones. Primary effluent and RAS were assumed to discharge to the anoxic zone along with recirculated mixed liquor from the last aerobic zone. Information used to calibrate the model included monthly averages for flow, BOD, TSS, sludge retention time (SRT), ammonia, volatile suspended solids (VSS), ph, temperature, sludge volume index (SVI), aeration basin DO, and TSS removal. Table 4-3 is a summary of the calibration of the Pro2D model. The table shows the parameters that were used to obtain the calibration and compares the results of the Pro2D model with the WWTP data. It was difficult to obtain an exact calibration, and, in the end, the model was primarily calibrated to minimize the difference between the modeled and observed mixed liquor suspended solids (MLSS) and waste activated sludge (WAS) because these parameters are the most important in predicting the capacity of the activated sludge process. As Table 4-3 shows, the calibration of MLSS and WAS was within 11 percent of the observed values. The Pro2D model predicted higher MLSS concentrations and more WAS than were observed in two of the three months modeled, even with the forced calibration. This means that the Pro2D model will tend to underestimate the capacity of the Wenatchee WWTP activated sludge process. The calibration exercise indicates that the WWTP staff may want to perform some checking of their flowmeters and sampling procedures. The calibration parameters used greatly distort other results, such as mixed liquor volatile suspended solids (MLVSS) and oxygen requirements. The MLVSS predicted by the Pro2D model are much less than the observed values, and the oxygen requirements are much too high. As a result, the oxygen 4-10

33 requirements predicted by Pro2D for this evaluation should not be used. A check of the results was made by measuring the chemical oxygen demand (COD) of the influent wastewater; this check indicated that the parameters used to obtain the best predictions of MLSS and WAS do not predict the COD/BOD ratio of the influent wastewater. This suggests that the WWTP data may have some inaccurate flow measurements or nonrepresentative sampling that is affecting their accuracy. It is recommended that the City investigate and confirm the accuracy of flow measurement and sampling. Particular attention should be paid to the WAS, MLSS, influent and primary effluent BOD, and TSS samples. The Pro2D model results discussed in this Facilities Plan are based on the calibrated model that uses the Wenatchee data. If it is found that there are some inaccuracies in the data and the standard municipal wastewater parameters are found applicable, the impacts are very significant. Use of the standard municipal wastewater parameters will reduce the predicted WAS and MLSS by 15 to 20 percent. This means that the model may be predicting 20 percent less treatment capacity than is actually available. If the influent strength from current sampling is found to be higher than the actual, then the predicted quantity of primary sludge is higher than is actually occurring, and the digester expansion is not required as soon as predicted in this Facilities Plan. TABLE 4-3 Calibration of Pro2D Model for Wenatchee WWTP Calibration Parameter Winter Summer Flow Average Average BOD U/BOD 5 ratio Nonbiodegradable VSS, % of total VSS 10% 17% Yh, aerobic Yh, anoxic fd, all zones COD of VSS, raw influent COD of VSS, aerobic biological b Calibration Parameter Pro2D Model Summer (July 2006) Summer (August 2006) Observed % Difference Pro2D Model Observed % Difference Primary effluent BOD 5 (mg/l) PE TSS, mg/l MLSS concentration (mg/l) 2,056 1, ,903 1, MLVSS concentration (mg/l) 1,398 1, ,281 1, % VSS of MLSS WAS (lb/d) 3,253 3, ,061 3,

34 TABLE 4-3 Calibration of Pro2D Model for Wenatchee WWTP Calibration Parameter Winter Summer Effluent CBOD* (mg/l) Effluent ammonia (mg/l) Effluent alkalinity (mg/l as CaCO 3) Calibration Parameter Pro2D Model Winter (January 2006) Observed % Difference Primary effluent BOD 5 (mg/l) PE TSS, mg/l MLSS concentration (mg/l) 2,951 2, MLVSS concentration (mg/l) 2,163 2, % VSS of MLSS WAS (lb/d) 3,930 3, Effluent CBOD* (mg/l) Effluent ammonia (mg/l) Effluent alkalinity (mg/l as CaCO3) Primary effluent TSS (mg/l) *Pro2D value is BOD 5 concentration; observed value is CBOD concentration. Glossary for Table 4-3: BODu ultimate BOD, typically the BOD after 20 days of incubation in the WWTP application. BOD 5 5-day BOD, biochemical oxygen demand after 5 days of incubation VSS volatile suspended solids, suspended solids that are combusted in a furnace Nonbiodegradable VSS volatile suspended solids that cannot be degraded by biological activity Yh ratio of biological solids produced per unit of BOD by heterotrophic bacteria, which varies for aerobic and anoxic conditions fd rate of endogenous activity used in the ASM2d model COD chemical oxygen demand, measure of the amount of oxygen used to decompose sewage using strong chemicals as oxidizers TSS total suspended solids, measurement of solids removed by filtering PE primary effluent MLSS mixed liquor suspended solids is the concentration of suspended solids in the aeration basins WAS waste activated sludge is the suspended solids removed from the activated sludge process CBOD carbonaceous BOD is the BOD 5 with an inhibitor added to prevent nitrification from occurring during incubation Alkalinity concentration of hydroxide, carbonate and bicarbonate ions and is a measure of the resistance of wastewater to change ph CaCO 3 calcium carbonate is a standard for expressing concentration of alkalinity 4-12

35 Another observed result of the calibration is the disparity between the predicted and observed effluent ammonia concentrations. Normally, this prediction is quite close, but the calibration prediction is 80 to 90 percent lower than the observed effluent ammonia concentration. This suggests that there may be something in the Wenatchee wastewater that is inhibitory to nitrification. Work in Wenatchee a few years ago showed that nitrification can at times occur as predicted, so this calibration result indicates that something is currently interfering with nitrification. The City has observed that the activated sludge process produces lower ammonia when operating in the step-feed mode, which is different than the modeling would predict in the absence of inhibition. It is possible that a toxic material is sufficiently diluted in the step-feed mode of operating the activated sludge process that the effect is reduced compared to the plug flow anoxic mode of operation. The City is continuing to investigate the potential causes and has evidence that the dewatering sidestream may be the cause. The City is considering modification of the schedule of biosolids dewatering to reduce the impacts. It should be noted that while the apparent inhibition is significant, the effect is nowhere near enough to cause ammonia violations of the NPDES permit Activated Sludge Process Capacity The calibrated Pro2D model was used to estimate the capacity of the activated sludge process. The Wenatchee WWTP has been nominally rated for 5 mgd average annual flow since publication of the October 1988 Wenatchee Wastewater Treatment Plant Improvements Engineering Report (CH2M HILL, 1988). In 1992 and 2004, improvements were made to maintain the capacity of the WWTP at this nominal 5-mgd average annual flow. Average annual flow, although simple and easy to understand, is not an accurate description of WWTP capacity. City staff has been effective in removing extraneous flows such as irrigation return flow and stormwater runoff from the sanitary sewer system. As a result, flows have not increased at the same rate as the population served and the BOD and TSS loading. Table 4-4 shows the changes in service population, average annual wastewater flow, and average annual influent BOD and TSS for the Wenatchee WWTP between 1980 and TABLE 4-4 Comparison of Population Served, Wastewater Flow, BOD, and TSS for WWTP in 1980 and 2000 Year Service Population Average Wastewater Flow (mgd) Average Influent BOD (lb/day) Average Influent TSS (lb/day) , ,750 5, , ,660 7,220 Table 4-4 shows that average wastewater flow increased 10 percent, but service population, influent BOD, and influent TSS increased roughly 40 percent four times higher. This means that the wastewater treatment processes sized for the BOD and TSS in wastewater must be larger to treat the wastes contained in an average of 5 mgd of wastewater flow. The activated sludge process and anaerobic digestion processes are both sized to treat BOD and 4-13

36 TSS in addition to flow and must be larger to treat an average of 5 mgd of wastewater due to increased BOD and TSS. Table 4-5 shows three estimates of the influent BOD and TSS that will occur when the average influent flow reaches 5 mgd. The first estimate is from Table 3 of the 1988 Engineering Report. The estimates were based on the assumption that the concentration of the BOD and TSS would remain constant using the concentration observed in 1985 and 1986 and that the ratio of maximum month to average would also remain constant. The second estimate is from the January 2003 Facilities Plan Amendment. These estimates were based on the assumption that the concentration of BOD and TSS would remain constant using the concentration observed in 2000 through June 2002, and assuming the ratio of maximum month to average would remain constant. There were large variations in BOD and TSS during this period of time, and the larger values were used for the estimates. The third estimate is based on the projections made for this Facilities Plan based on estimates from the 2008 draft Wenatchee Comprehensive Sewer Plan (City of Wenatchee), which is currently being prepared in parallel with this Facilities Plan. It assumes that future BOD and TSS from new service population will contribute lower per capita BOD and TSS, resulting in lower projected BOD and TSS when an average flow of 5 mgd is reached. The evaluation of capacity of the Wenatchee WWTP in this facilities plan is based on the third estimate the 2007 Facilities Plan column. TABLE 4-5 Estimates of BOD and TSS When Average Annual Flow Reaches 5 mgd Parameter 1988 Engineering Report 2003 Facilities Plan Amendment 2007 Facilities Plan Average annual flow Maximum month flow Average annual BOD 7,900 11,873 10,800 Maximum month BOD 10,300 13,006 11,826 Average annual TSS 8,400 11,757 10,700 Maximum month TSS 10,100 13,111 11,717 The calibrated Pro2D model was used to estimate the capacity of the activated sludge process by running the model with different flows and the BOD and TSS associated with those flows. The Pro2D model should provide fairly accurate estimates of activated sludge process capacity because it calibrated well for MLSS, and the capacity of the activated sludge process is limited by the solids loading rate for the secondary clarifiers. The solids loading rate is a function of the peak flow and MLSS concentration. The Pro2D model calculates the operating rate of each unit process, and the capacity can be estimated by comparing the operating rate to allowable operating rates based on good engineering practice. The model was run at the maximum monthly values for flow, BOD, and TSS. Maximum month loadings were used because the waste load to the WWTP varies and 4-14

37 needs to be able to handle the short-term higher loads. Maximum month is a reasonable time period because the activated sludge process operates at a long SRT and avoids some of the variance that would result using a maximum week loading because of the limited samples taken per week. Additional evaluation was done for the effects of operation at peak flows of 11 mgd for several hours because this condition requires the secondary clarifiers to operate at maximum loading rates and limits the maximum MLSS concentration in the aeration basins. MLSS concentration is a key parameter limiting the capacity of the activated sludge process. The initial evaluation was for operation of the activated sludge process in the plug flow with anoxic selector mode at 5.5-mgd flow, which is the estimated maximum month flow when the average annual flow is 5 mgd. Winter wastewater temperatures were used for this analysis because this is the limiting condition for WWTP capacity. Higher SRT is required when wastewater temperature is lower to oxidize ammonia biologically, and this requires higher MLSS concentration. Higher MLSS concentration increases the solids loading rate on the secondary clarifiers, and the solids loading rate at peak design flows limits WWTP capacity. Plug flow with anoxic selector is the preferred mode of operation because the anoxic selector helps control the growth of filamentous bacteria that can cause poor-settling activated sludge. Poor-settling activated sludge can cause poor effluent quality and NPDES violations. The Wenatchee WWTP has had a history of problems of filamentous bacteria causing violations of the NPDES permit. The Pro2D model predicted that the MLSS would be over 5,200 mg/l, which is too high because the solids loading on the secondary clarifiers would result in the loss of TSS in the effluent in excess of the NPDES permit. Appendix C-1 contains the output of the Pro2D model for this case. The second evaluation modeled operation of the activated sludge process in the step-feed mode at 5.5 mgd. The step-feed capacity was modeled assuming 12 percent of the primary effluent flow to first zone, 20 percent to the second zone, 40 percent to the third zone, and 28 percent to the fourth zone. The calibrated Pro2D model predicted the MLSS would be 3,000 mg/l to the secondary clarifiers. The Pro2D model predicts the secondary clarifiers would be able to handle this loading as long as the SVI was maintained to 150 ml/g or less. This would likely require periodic chlorination of the RAS to control filamentous bacteria and maintain the SVI at or below 150 ml/g based on the operating history of the Wenatchee WWTP because the anoxic selector would not be available in this mode of operation. Peak flow of 11 mgd could be successfully handled for several hours operating in step feed. Appendix C-2 contains the output of the Pro2D model for this case. The calibrated Pro2D model was used to determine the maximum capacity of the WWTP in the plug flow with anoxic selector mode, expressed as 4 mgd on an annual average flow basis. The Pro2D model was used to evaluate the WWTP at a maximum month flow, BOD, and TSS of 4.4 mgd, 9,460 lb/day, and 9,370 lb/day, respectively, the loading associated with an annual average flow of 4 mgd. The MLSS predicted in the aeration basins is 2,700 mg/l in the summer and 3,700 mg/l in the winter. Evaluation of the secondary clarifiers shows that the resulting solids loading rate is acceptable at typical dry weather flows, but that the secondary clarifiers would be overloaded to failure at the peak flow of 11 mgd. Changing from plug flow with anoxic selector to step feed reduces the MLSS to 2,300 mg/l. Step-feed operation of the activated sludge process is recommended when flows might cause the solids loading to exceed the secondary clarifier capacity. The 4-15

38 evaluation of the secondary clarifiers with MLSS of 2,300 mg/l shows that they can safely operate for a few hours with flows of 11 mgd. The Pro2D model results are summarized in Appendices C-3, C-4, and C-5 for these three conditions. The conclusions of the modeling of activated sludge capacity using the Pro2D model calibrated with recent operating data from the Wenatchee WWTP are as follows: Average flow capacity in the plug flow with anoxic selector mode is 4 mgd with operation in the step-feed mode during periods of peak flows that occur for a few hours per year in Wenatchee. Average flow capacity in the step-feed mode is 5 mgd. Therefore, it is recommended that the rated capacity of the Wenatchee WWTP is 5 mgd. At an average annual flow of 5 mgd, it is assumed that the maximum month flow is 5.5 mgd, peak flow to the activated sludge process is 11 mgd, maximum month influent BOD is 11,826 lbs/day, and the maximum month influent TSS is 11,717 lbs/day. This BOD and TSS loading is less than the capacity stated in the NPDES Fact Sheet because the estimated concentration of influent BOD and TSS is lower than the concentrations assumed for the capacity estimate used in the Fact Sheet. Appendix D contains information summarizing the WWTP design after the improvements were completed in September Included in Appendix D are site plans showing topography and sampling locations, design criteria, hydraulic profile and process schematic, and mass balance. These facilities will not need to be expanded until the average annual wastewater flow reaches 4 to 5 mgd, and this is projected to occur between 2018 and Some additional discussion of this recommendation is warranted to understand the assumptions that affect this recommendation and understand alternatives for enhancing the capacity of the activated sludge process if needed. First, the average flow capacity is based on the influent BOD and TSS values shown in Table 4-4, which assume that future population per capita BOD and TSS loadings are less than the currently observed values. If it turns out that the actual per capita BOD and TSS loadings remain unchanged, the average flow capacity will be less. Second, the modeling is based on the Pro2D model calibrated with Wenatchee WWTP operating data. This data may be erroneous. Based on experience using the model at other locations, it is anticipated that the data reported by the WWTP is on the high side and the model is under-predicting the actual capacity of the activated sludge process by as much as 15 to 20 percent. Third, it is assumed that the operational staff can operate the step-feed process effectively. The design flow splits to each aeration zone are important to gain the benefits of the step-feed mode of operation. WWTP staff has had limited experience operating the step-feed system and are working out the bugs in the system to gain experience and confidence with the activated sludge process in the step-feed mode. Finally, it is assumed that filamentous bacteria can be controlled in the step-feed mode to less than an SVI of 150 ml/g. Step feed is similar to the complete mix mode of operation, and 30 years of experience in Wenatchee have indicated that filamentous bacteria have historically been a problem. Chlorination of RAS has been shown effective controlling filamentous bacteria in Wenatchee and may be required often when operating continuously in the step-feed mode. Filamentous bacteria occurring in the activated sludge process have been associated with digester foaming in Wenatchee, and filamentous bacteria occurring in 4-16

39 the step-feed mode of activated sludge could trigger implementation of anaerobic digester foam improvements discussed later in this Facilities Plan. There are alternatives to consider to expand the capacity of the existing activated sludge process in the plug flow with anoxic selector mode of operation. One alternative is to add fixed film media to the activated sludge process to enhance ammonia oxidation at lower MLSS concentrations. This process modification is known as the IFAS (integrated fixed film activated sludge) process. The capacity of the activated sludge process is controlled by the maximum MLSS concentration that the secondary clarifiers can handle. A higher MLSS is required to achieve the SRTs necessary for nitrification, the oxidation of ammonia. This was demonstrated at the Broomfield, Colorado WWTP as documented in a paper presented at WEFTEC in 2006, Two Year Case Study of Integrated Fixed Film Activated Sludge (IFAS) at Broomfield, CO WWTP by Ken Rutt, et al. This would require installation of fixed film media and changing the aeration diffusers (based on current technology), but would have the benefit of no increase in sludge production and no chemical costs. Another option is to add chemicals ahead of the primary clarifiers chemically enhanced primary treatment (CEPT). The Wenatchee WWTP has the capability to add alum and polymer, which can be used for this purpose. Rapid mixing and flocculation facilities are needed to optimize the performance of this option. Use of the old aerated grit chamber may be sufficient to provide adequate mixing and flocculation. Plant scale testing in combination with bench testing to determine the soluble and colloidal fractions of COD is recommended to evaluate the potential of CEPT. Disadvantages of this approach are increased primary sludge production due to chemical sludge and cost of chemicals. Increased sludge production would accelerate the timing for construction of a new anaerobic digester. Another approach that might allow operation with reduced MLSS while maintaining nitrification is bioaugmentation. Bioaugmentation is treatment of the belt filter press filtrate stream which is warm and high in ammonia. This can provide a source of nitrifying bacteria that allow operation of the activated sludge process at a lower SRT and thus a lower MLSS. This will reduce the solids loading on the secondary clarifiers at peak flows and increase the capacity of the WWTP. Carbon addition for denitrification or alkalinity reduction are likely to be required. 4-17

40

41 CHAPTER 5 Future Conditions This chapter evaluates future population growth in the Wenatchee Urban Growth Area (UGA), and analyzes forecasted flows and wasteloads to the Wenatchee Wastewater Treatment Plant (WWTP) through the year The City s water conservation and flow reduction plan is reviewed, and the expectations for future industrial wastewater production in the UGA are evaluated. The future environment of the plant in relation to capacity, visual environment, odor, and effluent discharge are discussed and proposed measures to address these areas are described. 5.1 Population and Land Use The estimated number of persons connected to the Wenatchee WWTP are shown below in Table 5-1. These population estimates were developed in the draft 2008 City of Wenatchee Comprehensive Sewer Plan developed by the City of Wenatchee, and the details of the development of these estimates may be found in the Comprehensive Sewer Plan. TABLE 5-1 Users Connected to Wenatchee WWTP Parameter Estimated Connected Population 28,750 31,750 35,280 39,300 43,526 Two areas outside the City of Wenatchee UGA, Malaga and Monitor to Sunnyslope, are not included in the estimated connected population shown in Table 5-1 because these areas are not anticipated to be sewered prior to Land use within the city limits of Wenatchee is not expected to change over the next 20 years with the exception of the waterfront area. Land use changes are expected in the areas outside the city limits, and details can be found in the draft 2008 City of Wenatchee Comprehensive Sewer Plan prepared by the City of Wenatchee. 5.2 Forecasted Flow and Wasteloads This section presents the results of estimations of total flows and loadings to the City s WWTP through the year Water Conservation and Flow Reduction The City building department requires the use of national plumbing codes, which require water-conserving fixtures. Commercial and industrial users are charged based on their metered water use, which encourages flow reduction. 5-1

42 The State of Washington s new Water Use Efficiency Rule (WAC ) took effect on January 22, It requires the following: water systems to use water efficiently and demonstrate that they are doing so. Specifically, water systems must: Develop a plan through a public process and enact measure to manage water use. Reduce distribution system leakage to 10 percent or less. Install service meters within 10 years, if not already installed, to accurately account for water usage and leakage. Reporting annually on their progress in using water efficiently. The City is in the group of water systems to which the rules apply and will develop a strategy to meet the rule s requirements Future Industrial Wastewater It is very difficult to predict industrial use and wastewater production. The apple industry has undergone and continues to undergo many changes and has generally been reducing industrial operations that generate industrial wastewater for the City of Wenatchee to treat. There are currently no other known proposals for significant industrial water users to operate in the UGA. When proposals arise, the City will evaluate them individually for their effects on the wastewater conveyance and treatment system and will act accordingly. The estimates for future flow incorporate an allowance for industrial wastewater, which is partly based on existing WWTP flow data. Future industrial growth is anticipated to occur in the Olds Station area. The Olds Station area is mostly zoned industrial. Although current uses at Olds Station contain some industrial activity, the majority of uses are offices that send typical domestic wastewater to the sewer. There exists the potential for the area to be developed to include more industrial users Forecasted Flow and Wasteloads Table 5-2 summarizes average annual flow and waste load projections for the WWTP. Average annual flow projections were determined based on the estimated connected population in the indicated years as presented earlier in this chapter coupled with an estimated future unit wastewater contribution of 117 gallons per capita per day (gpcd) on a maximum month basis and includes contributions from non-residential sources. Flows calculated for future population were added to the 2005 WWTP flow to estimate future total annual average flow in selected years. The per capita flow value used was chosen in coordination with the City of Wenatchee Public Works staff and is based on existing data, estimated flow reductions from new sources due to water conserving fixtures and new piping, Ecology s guideline of 100 gpcd for residential flows (including I/I), review of I/I (it is low), and review of water use data. The current annual average unit flow was calculated to be 109 gpcd, including nonresidential sources. It was decided that the future unit flow would be less because of the 5-2

43 aforementioned reasons. Also, most future development is predicted to be residential; therefore, it is reasonable to use connected population as the indicator of flow. As the City reviews flow data over the years, the projections can be revisited in future plan updates. TABLE 5-2 Summary of Flow, BOD5 and TSS Projections for City of Wenatchee WWTP Annual Average Flow (mgd) a Annual Average BOD 5 Loading (lbs/day) b 7,000 7,600 8,300 9,100 10,000 Annual Average TSS Loading (lbs/day) b 6,900 7,500 8,200 9,000 9,900 Notes: a The per capita allowance for wastewater loading is 0.2 lbs/cap/day for new population for both BOD 5 and TSS and includes non-residential sources. b The per capita for new population is 100 gal/cap/day and includes non-residential sources. Projections of future average annual BOD 5 and TSS loadings are presented in Table 5-3. The projections were calculated based on annual average BOD 5 and TSS unit loadings of 0.20 lbs/capita/day for population added after This is lower than the current per capita loading rates of 0.24 lb/day, including non-residential sources. This assumption presumes that commercial and other sources of waste load will not increase at the same rate as the population of the city increases. Recently, influent BOD and TSS data for the WWTP have not increased at the same rate as the reported increase in population. The unit loading values used were chosen in coordination with the City of Wenatchee Public Works staff. The existing per capita values were considered to be too high to be used to estimate future waste loads because the City recently instituted a grease control program. As a result, there has been a significant reduction in loadings to the WWTP, and the City anticipates further reductions as the program expands and all facilities are brought into compliance. In addition, the loadings from fruit processing are anticipated to decrease as operations cut back and higher degrees of pretreatment are instituted. As noted above, future development is anticipated to be mostly residential, so using the Ecology guideline values of 0.20 lbs/ capita/day is reasonable. It is recommended that the City review waste load data every year to confirm that the increases in BOD and TSS are within the estimated quantities. Treatment processes such as the activated sludge and anaerobic digestion processes are more sensitive to increases in BOD and TSS than flow. Maximum 30-day, 7-day, and day loading rates were estimated by multiplying the average annual flow, BOD, and TSS loadings from Table 5-2 by the observed peaking factors in the years 2000, 2001, and first 6 months of 2002 as documented in Table 2-1 of the Final Facility Plan Amendment for Wenatchee Wastewater Treatment Plant Improvements (CH2M HILL, 2003). The peaking factor is the ratio of the observed loading of a parameter at a maximum condition divided by the annual average for a parameter. It is assumed that future peaking factors will be the same as currently observed. Table 5-3 summarizes the forecasted flow and waste loads for 2005, 2025, and the future when average annual flow is 5 mgd. Periodic review of the maximum loading parameters compared to the estimates is recommended to 5-3

44 confirm that the loading rates are not exceeding the planned for quantities. Higher maximum loading rates could require implementation of improvements sooner than this plan is projecting. TABLE 5-3 Forecasted Flows and Wasteloads Flow (mgd) Parameter Future Average annual Maximum 30-day Maximum 7-day Maximum day Peak Influent BOD (lb/day) Average annual 7,000 10,000 10,800 Maximum 30-day 7,700 11,000 11,800 Maximum 7-day 8,400 12,000 13,000 Maximum day 12,100 17,300 18,700 TSS (lb/day) Average annual 6,900 9,900 10,700 Maximum 30-day 7,600 10,800 11,700 Maximum 7-day 8,300 11,900 12,800 Maximum day 11,900 17,100 18,500 TKN (lb/day) Average annual 750 1,100 1,200 Maximum 30-day 1,100 1,600 1,800 Maximum 7-day 1,300 1,800 2,000 Maximum day 1,600 2,400 2, Future Environment Without Project Without implementation of this Facilities Plan, the following elements of the existing plant would remain unchanged: capacity, visual environment, odor, and effluent discharge quantities. 5-4

45 5.3.1 Capacity The existing WWTP has sufficient capacity to provide wastewater treatment until 2028 at projected wastewater growth rates without implementing improvements to the facility based on the average annual rated capacity of 5 mgd. After that time, the capacity of the plant and its various treatment mechanisms would need to be increased or the facility would no longer be able to accommodate the City s treatment needs. Ecology would likely impose a sewer moratorium when the WWTP approaches design capacity if they perceive the City is not committed to maintaining adequate capacity. If capacity is exceeded, either in the activated sludge or anaerobic digestion facilities, the WWTP would likely exceed the NPDES permit and the City would be vulnerable to fines from Ecology or to a citizen lawsuit Visual Environment The WWTP is located on an approximately 4-acre site between Worthen Street and the Riverfront Park, north of Orondo Street. The Wenatchee Convention Center and Coast Wenatchee Center Hotel are located across the railroad tracks. As shown in photographs discussed in Section 6.1.4, the plant is clearly visible to passersby on Worthen Street and to park visitors. In addition, the site can be seen from above from a pedestrian bridge that links the convention center with the park, as well as from the Coast Hotel, particularly the restaurant located on the top floor of the hotel. Areas around the WWTP continue to be developed and densified. The present public works facilities south of the WWTP are likely to be developed into a commercial use in the future. The North Wenatchee Business District lies to the north, and the Central Business District lies to the west. Additional provisions will be made for pedestrians near the WWTP, and a proposed waterfront pedestrian area lies directly south of the facility. As a result, the facility may receive increased pressure to modify or enhance its visual character to be more consistent with surrounding land uses. This facility plan proposes measures such as berms, landscaping, screening walls, and structural covers of facilities that could serve to enhance the visual environment of the WWTP. For additional information on these proposed improvements, see Section Without the implementation of this project and the recommendations it contains, the visual environment of the WWTP will remain unchanged for many years to come Odor Control Odor control is not currently provided at the WWTP. As the volume of influent increases at the plant over time, and thus the volume of sludge and biosolids produced increases, it is likely that odor may become more pronounced in the vicinity of the plant and potentially be experienced a greater distance away from the facility. Because of the increased odor, in conjunction with the development adjacent to the WWTP as discussed above, the facility may continue to experience increased pressure to provide odor control for its various facilities. Odor control can be achieved in many ways, and the facilities plan recommends that a detailed odor control plan be developed for the facility to determine the appropriate degree to which odor control should be implemented. 5-5

46 5.3.4 Effluent Discharge Currently, treated effluent from the WWTP is discharged into the Columbia River under provisions set forth in the NPDES permit. There are no changes proposed to the hydraulic capacity of the WWTP outfall and diffuser. The mixing zone will not be changed. Proposed improvements contained in this facilities plan include provisions to improve the effluent quality through additional treatment to meet Class A reclaimed water standards that allow water reuse for a variety of opportunities, one of which is irrigation for landscaping. At present, water from a nearby aquifer is used for landscaping irrigation that occurs on the WWTP site. 5-6

47 CHAPTER 6 Alternatives Improvements to the existing Wenatchee Wastewater Treatment Plant (WWTP) were evaluated that would accomplish the following: Increase capacity for the forecasted flows and wasteloads in response to Department of Ecology (Ecology) regulations Improve anaerobic digestion Reduce the impact of the WWTP on the surrounding land uses Reclaim wastewater for irrigation The evaluation included an estimate of costs for the potential improvements so that the City can develop a capital improvement program. The existing WWTP has sufficient capacity to provide wastewater treatment for many years without improvement, and staff has decided that detailed evaluation of capacity-related alternatives would not be useful because treatment technologies are likely to change prior to the need to implement the improvements. Representative treatment technologies were evaluated to establish a basis for estimating the cost of the future improvements. These representative treatment technologies have been successfully applied and are likely to include the alternatives that will be evaluated for implementation. Additional improvements were evaluated that are not related to the capacity requirements of Ecology and can be implemented at the City s option. These improvements are to improve the efficiency of anaerobic digestion and provide visual aesthetic mitigation, odor control, and Class A reuse water for irrigation. Specific alternatives are evaluated to improve the anaerobic digestion of waste activated sludge (WAS). WAS digestion technologies have improved, and the technologies are evaluated in this chapter. There are a variety of methods that can be used to reduce the visual impact of the WWTP, including berms and landscaping, screening walls, and structural covers for the facility. Odor control can be implemented to reduce odors from the WWTP. An odor control plan is recommended to determine the appropriate amount of odor control for the WWTP. Costs for odor control are presented as a range depending on the degree of odor control implemented. Additional treatment can also be provided to treat the water to produce Class A reuse water for irrigation. Representative improvements based on facilities successfully applied at other WWTPs in the Pacific Northwest were used for the purpose of estimating the potential costs of these facilities in Wenatchee. Conceptual costs of a new WWTP were also developed for comparison to the cost of expanding and improving the existing WWTP. The new facilities would include a new treatment plant, a new pump station at the existing WWTP, and new conveyance pipelines from the existing WWTP to the new WWTP and outfall. It was assumed that the new WWTP would be located within 5.5 miles of the existing WWTP and would use treatment 6-1

48 facilities similar to those of the existing WWTP. A site of 10 to 20 acres of relatively level ground would be needed for a new WWTP sized initially for an annual average flow of 8 mgd and having the capability of being expanded to serve the City for the next 50 years. Ecology requires an evaluation of alternatives and conceptual design of the recommended facilities in a facilities plan. This Facilities Plan was prepared at a programmatic level because the facilities required to increase capacity are not required for many years, and the other facilities are not required by Ecology and may be implemented at the City s option. An engineering report or facilities plan is required prior to making any improvements to a WWTP, but grant and loan eligibility requires preparation of a facilities plan. This Facilities Plan evaluates potential improvements at a level of detail sufficient to demonstrate adequate treatment capacity and develop a capital improvements plan to maintain adequate capacity so that the City can plan for future improvements. Detailed evaluation of alternatives and preparation of conceptual designs of recommended improvements will be done in a facilities plan amendment prior to proceeding with implementation of improvements. The facilities plan amendments describing specific improvements, combined with this programmatic Facilities Plan, will constitute the complete facilities plan. 6.1 Improvements to Existing WWTP This section evaluates improvements to the existing WWTP to meet these goals: Provide capacity for forecasted flows and wasteloads Improve anaerobic digestion of WAS Improve the visual appearance of the WWTP to neighboring properties Reduce odors from the WWTP Add reclamation facilities to allow use of the treated wastewater for irrigation The capacity-related improvements include expansion of the activated sludge process, anaerobic digestion expansion, and drying bed capacity expansion Expansion of the Activated Sludge Process Section 4.3 describes the evaluation of the activated sludge process that established the capacity of the activated sludge process at 5 mgd expressed as an annual average flow. This capacity is based on operation of the activated sludge process in the step-feed mode and classification as Class II facility for reliability and redundancy. Figure 6-1 shows the capacity of the existing activated sludge process compared to the forecasted annual average flow from 2005 to The figure shows that the capacity of the activated sludge process will be reached in the year If operation of the activated sludge process is limited to the plug flow with anoxic selector mode, and the capacity is limited to 4 mgd, then improvements will need to be operational in There are enhancements to the activated sludge process described in Chapter 5 that can extend the capacity of the activated sludge process beyond 4 mgd and thus the activated sludge process will likely require expansion sometime between 2018 and The time necessary to implement WWTP improvements is significant, and the City will be required to make decisions to begin planning and design of needed improvements many years before they are required. The following section describes analysis of the schedule for 6-2

49 potential improvements; this analysis shows that the City will be required to make decisions on expanding the activated sludge process as early as 2021 and possibly as late as 2025, depending on how the City decides to fund the improvements. This schedule is based on average flow capacity of 5 mgd; the time is reduced 10 years if the average capacity is 4 mgd. The minimum time to implement improvements using the conventional design, bid, and build approach is 3 years, assuming no delays between preparing the facilities plan amendment through construction. This scenario assumes a project that requires 4 months for preparation of the facilities plan amendment, 9 months for preparation of final design documents, and 15 months for construction. An additional 2 months are required for Ecology approval of the facilities plan amendment and final design documents, and 5 more months are assumed for bidding and award of a construction contract to obtain the minimum time for implementation. FIGURE 6-1 Activated Sludge Capacity Average Annual Flow (mgd) Year Forecasted Flow Activated Sludge Capacity If the City desires to obtain maximum Ecology funding through the Centennial or SRF loan process, the minimum time to implement improvements is nearly 7 years. Ecology requires applications for each step: facilities planning, final design, and construction. Applications are currently accepted only once per year in October. Loan money is available as early as July of the year following the submission of the loan application to as late as June, 2 years after making the loan application. It was assumed for this evaluation that loan and grant money would be available by October of the following year. Figure 6-2 shows a typical schedule assuming the City wishes to try obtaining maximum loan financing. However, there is no assurance that the City would receive loan financing if it applies. If the City decides to proceed using the approach of obtaining Ecology funding only for construction, the minimum time to implement improvements would be nearly 5 years. For purposes of estimating the cost of expanding the activated sludge process, the expansion is based on the representative treatment provided by a membrane bioreactor (MBR) system. The MBR would be run parallel to the existing conventional activated sludge process and would provide an average treatment capacity of 1 mgd, increasing the overall rated capacity of the activated sludge process and the liquids portion of the WWTP to an 6-3

50 ID Task Name Duration 1 Apply for facilities plan funding 0 days F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J 10/31 2 Final offer list 0 days 7/9 3 Facilities plan funding agreement 0 days 10/1 4 Prepare faciilites plan amendment 88 days 5 Ecology review and approval 44 days 6 Apply for design funding 0 days 11/2 7 Final offer list 0 days 7/9 8 Design funding agreement 0 days 10/1 9 Prepare final design 198 days 10 Ecology review 44 days 11 Apply for construction funding 0 days 10/31 12 Final offer list 0 days 7/9 13 Construction funding agreement 0 days 10/1 14 Bid 44 days 15 Award 66 days 16 Construction 330 days Task Split Progress Milestone Summary Project Summary External Tasks External Milestone Deadline Page 1 Figure 6-2 Project Schedule for Maximum Funding

51 average flow of 6 mgd. This is based on the future wastewater characteristics described in Chapter 5. MBR technology was assumed because it requires less land area than a conventional activated sludge process, and the available space for expansion of the activated sludge process is extremely limited on the east side of Worthen Street. Additional space is available on the west side of Worthen Street, but City staff requested that the analysis be performed for the east side of Worthen Street. The representative process includes these elements: Pump station Screening facilities Aeration basin MBR facility Ultraviolet (UV) disinfection Costs were based on a facility designed to handle 1.1 mgd at the maximum-month condition. MBR facilities cannot handle the same peak flows as a conventional activated sludge process, and it was assumed that the MBR facility would operate at essentially a constant flow rate of approximately 1.1 mgd. Approximately 1 mgd of primary effluent would be diverted to a submersible pump station and pumped to the parallel MBR facilities. Primary effluent would be screened through 2-mm band screens, which are used to protect the membranes from fibers and abrasive particulates. Following the screens, flow would pass through a conventional aeration basin, including an initial anoxic zone for nitrogen removal and conservation of alkalinity. Activated sludge from the end of the aeration basin would be recycled to the front of the anoxic zone. Sufficient aerobic tankage would provide for high removal of ammonia. Membrane facilities would be housed in a building. The membranes separate the treated wastewater from the activated sludge solids by sucking the water through 0.1-micron pores in the membranes. The pore size is smaller than individual bacteria and results in very low effluent TSS and turbidity. In addition to the tanks that hold the membranes, the building encloses other equipment for a complete MBR facility. This equipment includes pumps that suck the water through the membranes and membrane treatment equipment. Blowers are needed to provide aeration to the aeration tanks. A separate set of blowers would be needed to supply the air demand for membrane scouring. The building would also enclose the electrical equipment needed for the MBR facility. UV disinfection would follow the MBR facility and produce Class A reclaimed water before combining with the conventional activated sludge process effluent prior to discharge. Available space on the existing treatment plant site is extremely limited, and a 1-mgd average annual flow capacity MBR process appears to fit in the space shown in Figure 6-3. The screens would be located between the existing primary clarifier and pump station wet well, and the aeration basins would be sited directly east of the plant pump station wet well. The MBR itself would be located in the existing parking lot. This is a very tight layout, and additional engineering is recommended to confirm that the available space is sufficient. Figure 6-3 shows that the additional 1-mgd parallel MBR facility uses almost all the site area available. This expansion will leave little room for visual mitigation within the WWTP fence line and restrict the types of mitigation that can be used. It appears that a total annual average flow capacity of 6 mgd is the maximum that can be accommodated on the existing site east of Worthen Street. The City has additional site area available on the west side of 6-5

52 Worthen Street that might be capable of accepting another 4 mgd of capacity. Use of the site west of Worthen Street is an important issue for the City to decide. If use of this site for wastewater treatment is unacceptable to the City, additional wastewater capacity will be required on another site. This could be a second WWTP or a new WWTP. For purposes of this facility plan, a new WWTP was assumed to replace the existing WWTP and provide capacity for additional growth. The new WWTP is discussed in Section Anaerobic Digestion Improvements Three anaerobic digestion alternatives were developed to improve digestion of WAS and maintain sufficient capacity. Capital and annual operation and maintenance (O&M) costs as well as space requirements were estimated for each alternative Anaerobic Digestion Issues The existing plant has two primary sludge digesters and one secondary sludge digester. Primary sludge is digested in one primary digester and then the secondary digester. These digesters existed when the Wenatchee WWTP was upgraded from primary to secondary treatment in the early 1970s. Addition of thickened waste activated sludge (TWAS) from secondary treatment caused excessive foaming in the digesters. The foam entered the digester gas system and caused problems with the mixing system and the boilers. In 1992, a new primary digester was constructed for anaerobically digesting TWAS separate from the primary sludge. This digester was designed to prevent the foam from entering the gas system, and the digester freeboard was increased to account for the foam that was expected. TWAS feed to the digester occurs less than 24 hours per day because the gravity belt thickeners used to thicken the WAS operate less than 24 hours per day. As a result, feed to the digesters is not continuous. Late in the facility planning process, WWTP staff observed that foam was no longer occurring in the primary digester receiving only WAS. It was also reported that the foam stopped occurring in the fall of 2005 when the modifications to the activated sludge process became operational. It is known that nacardioform (a type of filamentous bacteria) are associated with anaerobic digester foaming, and it is possible that the reduction of these filamentous bacteria caused by the operation of the anoxic selector and plug flow aeration basins has resulted in elimination of foaming in the anaerobic digesters. The evaluation of anaerobic digestion foam reduction alternatives was prepared prior to the observation that foaming was eliminated. The analysis is included to document the evaluation of alternatives so that it is available in case foaming should resume in the future. Volatile solids reduction is still poor for TWAS-only anaerobic digestion, and it is recommended that TWAS be digested together with primary sludge to improve this. TWAS will not digest as well as primary sludge, but as a mixture the overall volatile solids destruction is sufficient to meet regulatory requirements. Digestion of combined primary and TWAS in the two primary digesters will extend the capacity of the existing anaerobic digesters because there is more primary sludge than TWAS. It is important the WWTP staff carefully monitor the anaerobic digesters for foam generation because foam can block the gas withdrawal piping, and the combination of gas and foam uplift pressure could cause a structural failure of the digester cover. The thin concrete dome on Primary Digester No. 1 is especially susceptible to this type of failure and has little freeboard. This is a reason why the 6-6

53

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55 current digestion process provided a separate digester for TWAS and included 5 feet of freeboard to accommodate foam generation. Assuming digestion of primary and TWAS together in Primary Digesters Nos. 1 and 2, and use of the secondary digester as a backup primary for when one of the primary digesters is out of service for maintenance, the digesters are projected to reach capacity within the planning period. City staff asked for an analysis of increasing the liquid operating level in Primary Digester No. 2 because foam is no longer occurring. CH2M HILL structural staff found that the operating level could be increased to elevation 653.5, an increase of 6.5 feet, and still meet current structural and seismic codes. This increases the effective volume of Primary Digester No. 2 from 308,000 gallons to 387,000 gallons, an increase of 26 percent. The firm capacity of the anaerobic digesters is based on the capacity with the largest single unit out of service, which in this case is Primary Digester No. 2. The capacity of the Primary Digester No. 1 and the secondary digester is 298,000 gallons each. The firm capacity of the anaerobic digesters is reached in 2020, assuming solids retention time of 15 days, primary sludge concentration of 3.5 percent, TWAS concentration of 5 percent, maximum month sludge quantities from the calibrated Pro2D model, and no recuperative thickening. Peaking factors for future sludge production were developed from quantities recorded in the plant s 2000 and 2001 discharge monitoring reports. Plant staff must limit the thickening of the primary sludge in the primary clarifiers because the plant has experienced problems with floating sludge in the primary clarifiers. Floating sludge increases the loading on the activated sludge process, which reduces the capacity of the activated sludge process when expressed as influent wastewater. Historically, this has not been an issue because the primary digester for primary sludge has had excess capacity. There are several options that can be used to extend the operating life of the existing anaerobic digesters and postpone construction of a fourth anaerobic digester. First, the capacity is based on the assumption of an anaerobic digester out of service during the maximum month sludge loading. There is a 41 percent difference between the maximum month and annual average sludge volume pumped to the anaerobic digesters. The City can schedule the maintenance of Primary Digester No. 2 to a non-peak time, and if a peak occurred when Primary Digester No. 2 was out of service, it could be placed back in service within a week on a temporary basis if needed. Second, the gravity belt thickener could be used to recuperatively thicken the digested solids if Primary Digester No. 2 was out of service during a peak loading period. Recuperative thickening removes water from the digester and returns thickened solids, increasing the solids retention time. Third, the City is investigating composting of solids from the WWTP and could compost some of the undigested WAS, reducing the loading on the anaerobic digesters. Less than 20 percent of the WAS would have to be composted without digestion to maintain a 15-day SRT with Primary Digester No. 2 out of service at maximum month loading and no recuperative thickening. Assuming the City is willing to implement one or more of these options to extend anaerobic digestion capacity, the existing anaerobic digesters can provide 20-day SRT at maximum month loading with all digesters in service until after A fourth digester (third primary digester) is needed after 2025 and would increase the digestion capacity to greater than 50 percent of the 2025 loads. This corresponds to approximately 7-mgd annual average influent flow at wastewater characteristics described in Section

56 It is necessary to be able to operate the secondary digester as a primary digester to provide the necessary firm digester capacity required by Ecology regulations because the quantity of sludge has increased. The secondary digester currently cannot be heated or mixed to allow operation as a primary digester. Additional piping is necessary, either to allow the mixing and heating equipment for one of the primary digesters to mix and heat the secondary digester, or to install new mixing and heating equipment for this digester. An analysis of alternatives to improve digestion of TWAS was performed before it was discovered that digester foaming associated with digestion of TWAS was no longer occurring. This analysis is still useful because there is no assurance that foaming will not reoccur in the future. Alternatives for improving the anaerobic digesters to improve digestion of TWAS, maintain sufficient anaerobic digestion capacity, and produce Class A biosolids were reviewed with City staff in a telephone workshop. The City has historically achieved a Class A biosolids product by drying the biosolids at the offsite sludge drying beds, but recently enacted Ecology regulations no longer allow this method of producing Class A biosolids. As a result, the drying beds now produce a Class B biosolids product. The regulatory requirements for Class B biosolids are different, and City staff are investigating the impacts on the City s biosolids management program. As a result, the City will evaluate its solids management alternatives, including evaluation of alternatives to produce Class A biosolids in a future sludge management study. The City is interested in evaluating co-composting its Class B biosolids with green waste. The anaerobic digesters at the Wenatchee WWTP are operated at mesophilic temperatures and produce Class B biosolids. Batch pasteurization prior to the mesophilic anaerobic digestion process is the one process that currently is accepted by EPA as a method of producing Class A biosolids, minimizes pathogen regrowth problems, and avoids a smelly thermophilic product. Production of Class A biosolids requires much greater energy to heat the sludge to pasteurization temperatures. Drying of the anaerobically digested Class B biosolids is another method of producing a Class A product, but this is even more energy intensive. Raw sludge can also be dried to produce a Class A product and this approach requires much less land area, but a large amount of energy is required. City staff decided not to pursue production of a Class A biosolids product at this time Evaluation of Alternatives The following two alternatives, identified in a workshop with a CH2M HILL anaerobic digestion expert and City staff, would potentially resolve the foaming issues related to the production of Class B biosolids from anaerobic digesters: 1. Convert to acid-phase digestion (APD) 2. Add sonication Both alternatives include the addition of a TWAS storage tank to allow continuous feeding of TWAS to the anaerobic digesters. It is believed that continuous feeding of TWAS may greatly reduce foaming that was observed previously. A third primary digester would be constructed in 2020 for methane gas production and solids stabilization for both alternatives. This third primary digester would be located in the northwest corner of the WWTP property, in the area of the existing retaining wall. For cost-estimating purposes, the 6-10

57 third digester was assumed to be the same size as the existing TWAS digester. A taller silotype design could be built to increase the digester volume; however, this would be the largest digester and would not contribute to the firm capacity (capacity with largest digester out of service) until one of the existing digesters is replaced with another silo-type design digester. If two or more silos were constructed to replace the existing primary and secondary digesters, the capacity for anaerobic digestion could be increased to greater than 9 mgd. This additional capacity would be needed if the City elects to expand the WWTP across Worthen Street and exceed the 7-mgd average flow capacity that is possible with four digesters having the current design. Alternative 1: Convert to APD For this alternative, anaerobic digestion operations would be converted to APD. APD is typically a mesophilic process that has been demonstrated on a large scale in the U.S. to eliminate foaming due to anaerobic digestion of TWAS. It enhances VSS destruction and produces approximately 10 to 15 percent more gas than conventional digestion. Anaerobic digestion is believed to occur in three steps. First, the solids are broken down to soluble compounds in a process called hydrolysis. The second step is the conversion of these soluble compounds into several organic acids and carbon dioxide gas. These two steps occur much more rapidly than the third step for many solids and are largely accomplished in the APD digesters. The third step is conversion of the organic acids to methane and carbon dioxide gas. The third step would occur in the existing anaerobic digesters. In conventional anaerobic digestion, all three steps occur in a single digestion tank. The same three steps occur in the APD process, but smaller digestion tanks are provided at the beginning of the process to concentrate the first two steps in these tanks. The gas from the APD tanks is relatively small in volume and must be mixed with the gas from the methane-producing tanks because this gas will not burn and is extremely odorous. When mixed with the digester gas from the other tanks, the digester gas mixture can be handled with standard digester gas equipment. The size of the APD digesters was estimated assuming a 1-day SRT at the maximum week flow and one APD digester out of service. For 2025 loadings, three APD digesters would be used. Initially, two of the three digesters would be operated in series, with one standby to provide operational and maintenance flexibility. The addition of a fourth APD digester would be needed around At that time, two APD digesters would be operated in parallel. Each APD would have a capacity of 29,500 gallons and would be 12 feet in diameter and 36 feet tall. A storage tank would be provided to blend the primary sludge and TWAS and allow continuous feeding of the APD digesters. Thickened raw sludge would be heated using low-pressure steam to 95ºF. Steam is required because conventional heat exchangers are not effective with thick sludge. The APD digesters would be mixed using pumped recirculation. The area adjacent to Worthen Street and in front of the existing primary digester would be sufficient for the four APDs and associated equipment. A twostory equipment building would be located between the APD digesters. One story of the building and part of the APD digesters could also extend below grade, reducing the visible height of the facility and APD digesters. Alternative 2: Add Sonication In Alternative 2, sonication would be added to the digestion process. Sonication uses ultrasound energy to rupture WAS bacterial cell membranes. Rupture of the bacterial cells 6-11

58 improves anaerobic digestion of TWAS and reduces foaming due to hydrophobic filamentous organisms. The process has been used in New Zealand and in Europe, but there are currently no installations in the U.S.. The sonication process involves pumping thickened sludge past ultrasound generators in a closed pipe. There is significant electrical equipment required to generate the ultrasound from electrical energy. The amount of electrical energy for ultrasound generation is similar to the mixing energy for the APD digesters. The process requires a small amount of space and would use the existing anaerobic digesters. Mechanical processes could be considered as an alternative to sonication. The Crown Biogest disintegration system operates at 12-bar (175 psi) pressure, which allows use of conventional progressing cavity pumps to create cavitation and cell rupture when the sludge is pumped through a nozzle. Because both of these processes are relatively new and unproven in the United States, a full-scale test is recommended during the procurement of these systems. Both of these processes are compact, and it is possible that sufficient size units could be trailer-mounted to facilitate testing. It is recommended that the City monitor foam production in the anaerobic digesters and installations of both alternatives for foam reduction. Both alternatives have limited experience in the U.S., and it will be useful to see what is learned as more installations are constructed. No improvements for foam reduction are needed if digester foam does not reappear Drying Bed Expansion The City of Wenatchee currently uses drying beds located about 10 miles south of Wenatchee to dry dewatered Class B biosolids. The biosolids from the anaerobic digestion process are dewatered using a belt filter press to approximately 12 to 17 percent solids, and then are trucked to the drying bed site. The drying beds are paved with asphalt and have concrete walls to contain the biosolids. All runoff from the drying beds is collected and contained in a lined retention basin. The City found that, after one year of drying, the biosolids could be tested for helmiths, viruses, and bacteria and be classified as Class A biosolids using Method 4 of Code of Federal Regulations (CFR) 503 and Ecology regulations. Ecology has deleted this method of meeting Class A biosolids, and the City will have to classify the biosolids as Class B. Composting is one approach that could be used to maintain the Class A rating under CFR 503 and Ecology regulations. Class B biosolids require additional monitoring and recordkeeping by the City and require restrictions to public access and crops grown at the locations where biosolids are used. Currently the City is proceeding with development of land application alternatives for Class B biosolids and obtaining the necessary Ecology approvals for their biosolids permit and proposed land application sites. New development has been considered in the vicinity of the sludge drying beds, and this could increase concerns about odor in the vicinity of the drying beds. The impact of development in this area should be considered by planning officials because it will be difficult to control the odors from the drying beds without significant expense. It is recommended that the issues related to the drying beds be evaluated in a comprehensive sludge management study. After discussions with City staff, it was estimated that the drying bed capacity should be increased by 50 percent to handle future solids quantities based on the City's operating 6-12

59 experience. This could be accomplished by constructing a new series of beds equal to onehalf of the existing facility size. These beds would be placed to the east of the existing beds and would share a common wall with the current drying beds. The new bed row would have one divider wall for a total of two new beds. Truck access would be provided by extending the existing gravel road around the perimeter of the new beds and providing gaps in the wall for bed entry, similar to the existing bed access. In addition to the new beds, improvements to the existing drying beds would be made to further increase capacity. These improvements would involve removing two inside walls in each bed row to double the individual bed size, and connecting the south bed walls and paving the area between to use the existing road space as additional drying bed area. A second stormwater retention pond would be constructed to the east of the existing pond to capture increased site runoff. The gravel road would be continued around the new pond for access. A 1,000-square-foot (sf) area in the existing gravel parking area would be paved for storage purposes as well Visual Aesthetic Improvements This section evaluates methods and costs of making visual aesthetic improvements to the WWTP. Public interest in the appearance of the WWTP resulting from the construction of Riverfront Park and new development adjacent to the WWTP may lead to the desire for visual mitigation of the WWTP site or consideration of moving the WWTP to a new location. This section discusses three different levels of visual mitigation to allow the City to make informed decisions on approaches for making improvements to the WWTP. The WWTP is located on an approximately 4-acre site between Worthen Street and the Riverfront Park, north of Orondo Street. The Wenatchee Convention Center and Coast Wenatchee Center Hotel are located across the railroad tracks. The plant is clearly visible to passersby on Worthen Street and to park visitors. In addition, the site can be seen from above from a pedestrian bridge that links the Convention Center with the park, as well as from the Coast Hotel, particularly the restaurant located on the top floor of the hotel. Photos 1 through 10 show the WWTP from ground level from various locations in the park and from Worthen Street. Photos 11 through 13 show views of the WWTP and equalization basin from the pedestrian bridge. Photos 14 and 15 show the WWTP from the restaurant on the top floor of the hotel. 6-13

60 PHOTO 1. Wenatchee WWTP Administration Building from Worthen Street PHOTO 2. Wenatchee WWTP Digester Complex from Across Worthen Street PHOTO 3. Primary Clarifier and Digester Area from Worthen Street 6-14

61 PHOTO 4. Wenatchee WWTP Headworks from Worthen Street PHOTO 5. Existing Digester and Solids Building from Riverfront Park PHOTO 6. Secondary Clarifier at Plant Fence Line from Within The Park 6-15

62 PHOTO 7. UV Facility and Generator Building from Park Trail PHOTO 8. WWTP from the North, Inside the Park (Several trees provide existing limited visual screening.) PHOTO 9. Digesters from Riverfront Park (Limited screening is provided by existing trees.) 6-16

63 PHOTO 10. Park Railroad Tracks Adjacent to UV Building and Plant Fence Line PHOTO 11. Aeration Basins from Pedestrian Bridge PHOTO 12. South End of WWTP from Hotel Restaurant 6-17

64 PHOTO 13. North End of WWTP from Hotel Restaurant PHOTO 14. Flow Equalization Basin from Pedestrian Bridge PHOTO 15. Additional View of Aeration Basins from Pedestrian Bridge 6-18

65 If odor control is employed in the future, its covers and ductwork will also be visible beyond plant property. A typical aluminum odor control cover and associated piping are shown in Photo 16. PHOTO 16. Typical Aluminum Odor Control Cover and Ducting for Primary Clarifier at Bremerton Wastewater Treatment Plant Three methods of visual mitigation that have been successfully used at other WWTPs are earthen berms and vegetation, perimeter walls, and structures that cover facilities. Earthen berms and vegetation consist of a landscaped strip around the perimeter of the facilities. The vegetation would be a mix of shrubs and trees appropriate for the Wenatchee area. Evergreen trees provide the most complete screening, but require substantial space and consume large amounts of water. Trees also shed leaves and needles, and this is not desirable near open wastewater treatment tanks because these debris can cause operational problems in the WWTP. Berms can add to the effectiveness of the vegetation, particularly lower growing shrubs and even grass; however, berms require a great deal of space. This option requires a substantial footprint and is probably only practical for the eastern side of the WWTP if located in the park and on the eastern side of the equalization basin along Worthen Street. The miniature railroad located on the fence line near the secondary clarifiers could also limit this method. This method would not be effective for screening the views from the hotel or restaurant. Another method that could be used alone or with berms and vegetation is a wall constructed around the plant along the perimeter. Like the landscaping method, this would mitigate views of plant structures from the park and Worthen Street at ground level. The advantages of a wall are that it requires less space than berms and vegetation and does not require any water. For purposes of estimating costs, it was assumed that the wall would be approximately 8 to 10 feet high around the plant and three sides of the flow equalization basin. It was assumed that the wall would be about 15 feet high on the west side of the equalization basin to better shield the basin from views from the hotel. It also was assumed that the wall would be cast-in-place concrete construction, similar to a freeway sound wall. A third method for visual mitigation involves covering wastewater basins with structures to make them look like buildings and blend the site with the surrounding neighborhood. To be most effective, all the structures at the WWTP would be developed to establish an overall architectural concept for the site; this would likely require some modification of the existing 6-19

66 structures to complete. The Vancouver Marine Park Water Reclamation Facility in Vancouver, Washington, is one example of visual mitigation that uses a combination of vegetation, structures over the wastewater tanks, and an overall architectural theme with the other buildings. Pictures of the facility are included as Photos 17 through 20 and provide an example of the highest level of screening that has been performed at a WWTP in the Northwest. Note that the structures do not actually enclose the wastewater tanks and do not provide odor control; they only provide visual mitigation. This method would provide the highest degree of visual mitigation for views from the hotel and restaurant. It is recommended that a detailed study of visual mitigation be performed to determine the appropriate improvements desired. This study would evaluate the various methods and involve work with the City to determine the improvements desired and their costs. Typically, computer modeling is used to help decisionmakers visualize the effects of different improvements. PHOTO 17. Vancouver Marine Park Water Reclamation Facility from Above PHOTO 18. Vancouver Marine Park Secondary Clarifiers at Plant Fence Line 6-20

67 PHOTO 19. Vancouver Marine Park Aeration Basin and Blowers PHOTO 20. Vancouver Marine Park Secondary Clarifier. (Visual screening does not completely enclose the clarifier.) Odor Control Improvements Odor control is currently not provided at the WWTP. This section evaluates facilities for providing odor control for the following elements of the WWTP: Headworks, including the influent junction box, plant pump station wet well, grit works, and screening area and grit/screenings loading area in the headworks facility Primary clarifiers Solids handling building, including the belt filter press room, sludge blend tank, and truck loading area Aeration basins Secondary clarifiers and RAS wet well 6-21

68 In the Pacific Northwest, when odor control is provided for a new WWTP, the first three categories of facilities receive odor control because they are the largest source of odors at a WWTP. Typically, odor control consists of single-stage chemical scrubbers that use sodium hydroxide and hypochlorite to remove hydrogen sulfide. The scrubbers can be designed to remove 90 to 99 percent of the incoming hydrogen sulfide, a level of odor control sufficient at most WWTPs where odor control has been required. With this level of odor control, objectionable odors are generally not discernible in the vicinity of the WWTP, but, under certain conditions, odors will be very noticeable. Space limitations will limit the types of odor removal facilities that can fit on the Wenatchee WWTP site. Recently, biological scrubbers have been used alone or in combination with chemical scrubbers. To show a range of costs for decisionmaking, odor control costs were also estimated for control of all of the sources listed above. In addition, a very high level of odor treatment was assumed. Two stages of chemical scrubbers followed by activated carbon was assumed to evaluate this maximum level of odor control. Two-stage chemical scrubbers can be designed to use different chemicals to remove other odorous compounds or to achieve higher removal efficiencies of hydrogen sulfide. Activated carbon can be added to chemical scrubbers to remove additional odorous compounds and achieve the highest level of odor control. Odors would not be detectable in the vicinity of the WWTP under nearly all conditions with this level of odor control. Open process basins require covering to contain the source of odorous air. The primary clarifiers, aeration basins, and secondary clarifiers have large spans that require a significant structure to support the covers. Aluminum is often used because of its corrosion resistance. These structures can be external trusses or domes and present a significant visual profile that may require screening to be acceptable to the public. These covers should be considered in the visual aesthetic planning work described in the previous section. City staff requested that this evaluation provide information to allow the City to develop a capital improvements plan for the WWTP and defer the detailed evaluation of alternatives for a later study. A detailed odor control study is recommended that will accomplish the following: Evaluate the facilities that need odor control Determine the level of odorous air treatment to be provided Evaluate alternative odor control technologies Evaluate odor containment alternatives Determine appropriate ventilation rates Evaluate ventilation alternatives Quantify the levels of odor that will result The odor control study should evaluate alternatives and develop the preliminary design of the odor control facilities and a budget-level cost estimate. This evaluation will be used to develop a range of potential costs for odor control for use in preparing the City s capital improvement plan for the WWTP. 6-22

69 6.1.6 Reclaimed Water Facilities This section considers coagulation and rapid sand filtration of secondary effluent as a representative technology to produce Class A reclaimed water. The MBR described earlier can produce Class A reclaimed water without filtration. Production of Class A reclaimed water may be desired before the MBR facility is needed or in a quantity greater than 1 mgd. A separate reclaimed water facility using effluent filters using activated sludge effluent is evaluated. Effluent filters also have the benefit of having much lower capital cost than MBR. Class A water must meet an average effluent turbidity of 2 NTU (Nephelometric Turbidity Unit) with a maximum of 5 NTU prior to disinfection. Rapid sand filters are a conventional filtration technology that decreases turbidity and reduces the number of virus and pathogens prior to a disinfection process. As particulates are collected by the sand filter, pressure across the filter bed increases and filter removal capacity decreases. Backwashing is used to clean the filter media and restore removal capacity. This could occur at a predetermined set-point based on head loss, effluent turbidity, time, or operator preference. Coagulant addition is required prior to filtration for the purpose of reclaimed water. Chlorine disinfection would be used following filtration, prior to discharge. It should be noted that MBR treatment also produces Class A effluent, and this product could be used in conjunction with the effluent filters described here, or membranes could be used instead of conventional filters. The reclaimed water facilities described in this section are standalone facilities that can be implemented independently of the MBR facility. Analysis of membranes and various conventional filters is recommended prior to implementation of the reclaimed water facilities. For purposes of estimating the cost of reclaimed water facilities at the Wenatchee WWTP, the following facilities were assumed. A submersible pump station located below grade would pump secondary effluent to the filters. A single-media, rapid sand filtration system could be located east of the existing chlorine building and storage shed, adjacent to the secondary clarifier. Filter equipment could be housed east of the filters in the area along the fence. This system would include four, 250-sf filter cells, a backwash supply tank, a backwash waste tank, backwash pumps, and scour air blowers. The facility could provide up to 4 mgd of filtration capacity with one filter out of service. Filter effluent would undergo chlorine disinfection and be pumped to a minimum 80 psi (pounds per square inch) for use as irrigation water in the Riverfront Park. This facility was assumed to include a submersible pump station, four, 250-square-foot filters, backwash tank, backwash pumps, air scour, chlorine disinfection, and pumping to an irrigation system provided by others Miscellaneous Maintenance Improvements WWTP staff are having to unclog the influent pumps and primary sludge pumps on a nearly daily basis because of clogging with rags. This activity is requiring large amounts of labor and is an unpleasant task that risks injury to the operators because of potential contacts with sharps. City staff have asked for improvements to reduce the problems due to ragging. Centralia and LOTT have had success eliminating ragging at two pump stations by using Wemco Hidrostal pumps instead of traditional nonclog centrifugal pumps. Both had serious ragging problems with traditional nonclog centrifugal pumps, which have been eliminated by use of Hidrostal pumps. Hidrostal pumps are a screw centrifugal pump with a specially 6-23

70 designed impeller that passes ragging materials rather than allowing the material to accumulate on the impeller. It is recommended that Hidrostal pumps be used to solve the ragging problem of the influent pumps. Fine screens with 1/4-inch-diameter holes rather than 3/8-inch slots will improve the removal of debris from Wenatchee influent wastewater and reduce primary sludge pump plugging and reduce the recognizables in the biosolids. The 3/8-inch mechanically cleaned screens installed in 1992 were a major improvement compared to the existing comminuters that the WWTP used prior to that time. Perforated plate escalator screens have become popular in the early 2000s because WWTPs need to remove more and smaller debris from wastewater. Perforated plate escalator screens are a slowly moving series of plates with punched holes through which the wastewater passes. The plates move out of the wastewater and are cleaned using rotating brushes and water sprays. The small holes result in the removal of fecal material, and a washer-compactor is recommended to clean the screenings before disposal. The washer agitates the screenings and sprays them with water to remove fecal material and then the screenings are compacted to remove water. Currently the WWTP has screenings compactors only. Washing the screenings will help reduce the odors and improve acceptance by the solid waste disposal company. It is recommended that perforated plate escalator screens and washer-compactors be used to solve the ragging problem with the primary sludge pumps. The quantity of screenings that must be disposed of will increase two to three times compared to the present volume of screenings disposed. 6.2 Cost Estimates for Evaluated Facilities This section presents the estimated capital costs of the potential improvements described in Section 6.1. Annual O&M costs are provided for some facilities. All costs are expressed in January 2007 dollars. Because many of these improvements are not likely to be implemented for many years, it is critical that these costs be increased for inflation for capital planning purposes. The cost estimates in this Facilities Plan were calculated based on standards developed by the American Association of the Advancement of Cost Engineering International (AACEI), formally referred to as the American Association of Cost Engineers. The AACEI cost estimate classification system has five levels of accuracy. Figure 6-4 shows how the accuracy of the cost estimate increases as the level of engineering and project definition increases. Class 5 estimates are produced when the amount of engineering performed and project definition is very low. As a result, the accuracy of the cost estimate is correspondingly low +100 percent to -50 percent. Class 1 estimates are produced after final engineering design and the project definition are complete. A Class 5 conceptual cost estimate is generally a concept, screening, or feasibility cost estimate. It is generally developed using a capacity ratio or cost curve method of cost estimate development or a parametric cost model. Class 4 schematic cost estimates are generally a study or feasibility cost estimate and could be considered a pre-design cost estimate. Schematic estimates are developed using the pre-design report and information, and can be produced with parametric models and cost factoring. CH2M HILL estimators prefer to have some level of quantity takeoff of major items as well as equipment quotes for a Class 4 estimate. It is usually performed at the end of the schematic design phase, based 6-24

71 FIGURE 6-4 Construction Cost Estimate Accuracy Ranges on 1 to 15 percent +/- design information. Class 3 design development cost estimates are commonly considered a budget, authorization, or control estimate, with semi-detailed unit and assembly level costs. More estimate detail is included than for schematic cost estimates, and there is less factoring of costs and allowances. It is generally performed at the midpoint development phase, based upon 10 to 40 percent +/- design information. A Class 2 construction documentation cost estimate is considered a control estimate or bid-tender cost estimate. It is developed near the end of the design phase and is generally considered the engineer's final estimate to which bids are sometimes compared. It requires the greatest amount of detailed takeoff and unit-price development, and updated equipment quotes are obtained. Class 1 construction documentation cost estimates are also considered control or bid-tender cost estimates. Cost estimates are only considered Class 1 when the estimate has been completed with 100 percent construction bid documents and the construction plans and specifications are 100 percent complete. Costs estimates in this facilities plan are Class 5 estimates and are +100 percent and -50 percent of the actual project cost. These cost estimates include the following percentage allowances for costs that cannot currently be quantified due to lack of engineering definition at this stage of analysis: Contractor overhead 10% Contractor profit 8% General conditions 10% Contingency 30% Market conditions 15% 6-25

72 Washington State sales tax 8% Engineering, permits, and administration 25% The percentages are based on typical costs for this type of project. Contractor overhead, contractor profit, and general conditions are typically included in bids for this type of work and represent costs experienced by a contractor performing this type of work. Contingency is added to cover unknown costs and decreases as the project becomes better defined. Market conditions percentage is based on current conditions and will vary depending on the bidding climate for this type of project. This percentage is based on bidding several recent projects in the Northwest. Washington State sales tax is applicable for the construction of these types of facilities. The percentage allowance added for engineering, permits, and administration will vary depending on the scope of services to be provided. Table 6-1 summarizes the cost estimates for the improvements described in Section 6.1. Costs for expansion of the activated sludge process, visual aesthetic improvements, odor control improvements, and reclaimed water facilities are for representative processes used to estimate potential costs and are not recommended facilities determined through engineering evaluation of alternatives. Engineering evaluation of alternatives is recommended prior to selecting facilities appropriate to Wenatchee. The representative technology used has been successfully implemented at other wastewater treatment plants in the Northwest and would be an alternative that could be considered in an engineering evaluation. For anaerobic digestion, alternatives to the existing system were evaluated. The costs for APD are displayed for both digestion with a new future primary digester and for APD without a new future primary digester. Specific improvements were evaluated for the sludge drying beds. Table 6-1 shows additional annual operation and maintenance (O&M) costs for expansion of the activated sludge process and anaerobic digesters. These O&M costs represent the incremental cost for adding the facilities described earlier in this chapter. Costs include additional labor, electricity, and materials for O&M of these additional facilities. O&M cost estimates were not included in the scope of work for some facilities and, therefore, were not estimated. Table 6-1 also shows costs of studies that are recommended prior to implementing new facilities. The additional studies include a sludge management plan, a visual mitigation plan, and an odor management plan. These studies are in addition to the engineering studies needed for the specific facilities that are proposed and deal with subjects outside the scope of wastewater facilities planning. These studies would affect the WWTP improvements and would, therefore, require a facilities plan amendment.. The sludge management study plan is recommended to evaluate alternatives for use and disposal of the biosolids produced by the WWTP and should identify where the City can ultimately place the biosolids and the level of treatment required. Because it will identify the solids treatment, the study should be completed prior to major expenditures to improve the anaerobic digesters. Preparation of a visual mitigation plan is recommended to identify the appropriate visual mitigation for the WWTP. This plan would evaluate the various alternatives to help the City 6-26

73 TABLE 6-1 Summary of Improvement Cost Estimates Anaerobic Digestion Visual Aesthetic Improvements Odor Control Improvements New Influent Pumps New Fine Screens Expansion of Activated Sludge Process Acid Phase Digestion Future Primary Digester with Acid Phase Digestion New Primary Digester Sonication Mixing and Heating for Secondary Digester Drying Bed Expansion Low Vegetation and Berms Medium Screen Walls, Vegetation and Berms High Building Structure Screen Walls, Vegetation and Berms Typical New Northwest Wastewater Treatment Plants with Odor Control Maximum Odor Control Reclaimed Water Facilities Total Construction Cost a $180,000 $1,000,000 $14,100,000 $6,200,000 $4,200,000 $5,800,000 $4,300,000 $550,000 $900,000 $300,000 $3,000,000 $18,900,000 $3,500,000 $11,500,000 $5,900,000 Total Project Cost b $240,000 $1,300,000 $17,000,000 $7,500,000 $5,100,000 $7,000,000 $5,200,000 $740,000 $1,100,000 $400,000 $3,600,000 $22,700,000 $4,200,000 $13,800,000 $7,100,000 Annual O&M Costs c NE NE $320,000 $104,000 $53,000 $53,000 $94,000 NE NE NE NE NE NE NE NE Study Costs $100,000 to $200,000 $100,000 to $300,000 $100,000 to $150,000 Notes: Costs for expansion of the activated sludge process, visual aesthetic improvements, odor control improvements, and reclaimed water facilities are for representative processes used to estimate potential costs and are not recommended facilities determined through engineering evaluation of alternatives. Costs are Class 5 accuracy, +100% to -50%, and are expressed in January 2007 dollars. a Includes allowances for contractor overhead (10%), contractor profit (8%), general conditions (10%), contingency (30%), and market conditions (15%). b Construction cost increased by allowances for sales tax (8%) and for engineering, permits, and administration (25%). c Annual O&M costs represent the increase in O&M costs for the additional facilities and do not represent total O&M costs for the WWTP. NE not estimated because O&M cost estimate not included in scope of work. 6-27

74 decide on the appropriate visual mitigation. Often, computer and physical modeling are used to help individuals visualize the impact of various improvements. Public involvement is typically an important element of these types of studies. Project teams often include engineers, landscape architects, building architects, and cost estimators to develop and evaluate alternatives. This plan would develop a concept for the entire WWTP and identify all the recommended improvements necessary to achieve the desired visual mitigation. Preparation of a visual mitigation plan is recommended prior to construction of any major facilities or improvements to the visual appearance of the WWTP. An odor management study determines the desired level of odor control for the WWTP and includes characterization of odor sources, modeling of various levels of odor control, and evaluation of specific odor control facilities to achieve the desired level of odor control. Public involvement is typically an important element of the odor control studies. Preparation of an odor management plan is recommended prior to construction of odor control facilities. 6.3 Cost Estimate for New WWTP The cost of a new WWTP was estimated to allow the City to compare the cost of improving the existing WWTP to the cost of a new WWTP at a new site. A site was assumed to be located within 5.5 miles of the existing WWTP. The site was assumed to be 10 to 20 acres in size to accommodate the wastewater treatment needs of the City for the next 50 years. An allowance of $2,000,000 was used for property acquisition. Costs were estimated for facilities with 8-mgd average annual flow with characteristics estimated in this facilities plan and a peak flow of 24 mgd. Facilities assumed for this analysis included modification of the existing influent pump station, conveyance pipeline, raw sewage pump station located near the new WWTP, enclosed screening and grit removal, covered primary clarification, activated sludge aeration basins similar to existing, secondary clarification, ultraviolet disinfection, enclosed gravity belt thickening and belt filter press dewatering, APD anaerobic digestion, and a new outfall to the Columbia River. Odor control was assumed for the headworks, primary clarification, and solids handling. The total project cost for the new WWTP is estimated to exceed $160 million. This cost does not include annual O&M costs. The City decided to expand the WWTP to the west of Worthen Street rather than consider constructing a new WWTP at this time. The alternative of constructing a new WWTP is eliminated from consideration in this facility plan. 6.4 Evaluation of Alternatives and Conceptual Design Additional studies were conducted to further evaluate alternatives and develop conceptual designs for drying bed improvements and influent pump station because City staff decided to implement improvements for these facilities within the next year. This section presents evaluation of alternatives and conceptual designs for these facilities. 6-28

75 6.4.1 Drying Bed Improvements The City has chosen to initially expand the drying beds by removing the north-south interior walls and paving the center road between the existing beds with low-permeability asphalt concrete liner, similar to the existing pavement. The pavement job mix formula should produce a combined gradation of aggregate within the limits defined in Table 6-2. Three new walls running east-west will be constructed across the existing access road to create four equally sized beds, adding approximately 20,000 sf of drying bed area. New 20-foot access openings will be created in the west walls of the two interior beds as well. Onsite runoff will be detained by the drying beds and existing evaporation pond. Conceptual demolition and construction plans and sections are shown in Figures 6-5 and 6-6. Design criteria for this expansion are shown in Table 6-3. A 4,900-sf area adjacent to the northeast pond will also be paved to serve as a vactor dump pad. TABLE 6-2 Aggregate Bituminous Surface Course Sieve Designation (Square Openings) Percentage By Weight of Aggregate Passing Sieves 1/2 inch /8 inch /4 inch U.S. No U.S. No U.S. No U.S. No Asphalt cement (percent by total weight) Total voids in mix Coefficient of Permeability Marshall Stability (minimum) (35 blows) 7.5 to 11 percent 2 percent maximum Less than 1 x 10-7 cm/sec 750 lb. TABLE 6-3 Drying Bed Expansion Design Criteria Parameter Value Number of beds 4 Bed dimension, each Bed area, each Drying bed runoff storage volume Evaporation pond runoff storage volume 100 ft wide, ft long 25,133 sq. ft. 45,833 cu. ft. 56,900 cu. ft. 6-29

76 There are two options for demolishing the existing walls: 1) Jackhammer the concrete to 6 inches below the existing pavement surface, and use a torch to cut the rebar. Place 3 inches of crushed surfacing, and then 3 inches of lowpermeability asphalt concrete liner. Reflective cracking in the asphalt is anticipated with this demolition option. 2) Excavate on the side of the wall adjacent to the center gravel road and use a concrete saw to remove the wall so it is flush with existing grade. This option would only be successful if there is sufficient clearance to use the saw. The estimated project cost for the drying bed improvements is $314,400. This cost includes a 30 percent contingency, contractor mobilization, and sales tax Runoff Detention Runoff from the sludge and stormwater will be retained and evaporated within the drying beds and the existing evaporation pond. At a minimum, the drying beds and evaporation pond can store runoff generated by the 25-year, 24-hour storm event in addition to mean annual precipitation. The existing evaporation pond has a storage capacity of 56,900 cu. ft., with a 5-foot sidewater depth. In order to retain runoff within the drying beds, the two new interior bed access openings will be raised 6 inches above grade, while the existing south bed access will be raised to 4 inches above grade. Runoff in excess of drying bed storage capacity will overflow south to the evaporation pond through notches in the new dividing walls and the south bed access opening, as noted in Figure 6-6. The west access road will be regraded to drain toward the drying beds and contain any potential contaminated runoff generated by truck traffic. A new trench drain will be installed and tied into the existing drain system to collect runoff from the vactor dump pad. A water budget cycle spreadsheet was prepared using the evaporation pond design method outlined in Ecology s 2004 Stormwater Management Manual for Eastern Washington. Water budget cycles for the drying beds and existing evaporation pond were calculated separately. Areas tributary to the drying beds include the new drying beds, gravel area surrounding the new vactor dump pad, and west access road. Areas that drain directly to the evaporation pond are the new vactor pad, pond perimeter road, and the pond itself. Mean annual precipitation and pan evaporation values were obtained from the Wenatchee Experimental Station, with a period of record of 1950 to Evaporation was adjusted from the pan evaporation values using an 80-percent adjustment factor. It was assumed that water depth is constant across all drying beds, and once the drying bed runoff storage volume is exceeded, water overflows south to the evaporation pond. This overflow volume was then used in the evaporation pond water budget cycle as additional pond inflow. The analysis assumes the beds and pond contain dead storage equivalent to runoff from the 25-year, 24- hour storm. The water budget cycles were iterated until the pond volume requirement reached a steady state. Calculation results show the expanded drying beds and existing evaporation pond have runoff storage capacity in excess of the volume needed to detain and evaporate the 25-year, 24-hour storm event plus mean annual precipitation. The required storage volume initially increases before reaching a steady state condition at approximately 47,000 cu. ft., or about 85 percent of the evaporation pond capacity. The water budget cycle spreadsheet and a 6-30

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81 graph showing required storage volume over time is included in Appendix D-2. The City will regularly monitor the evaporation pond volume to ensure its storage capacity is not exceeded. If the pond reaches its storage capacity, the City will pump out the water and haul it to the WWTP for treatment and disposal. 6.5 Influent Pump Station The Wenatchee WWTP has an influent pump station with 6 pumps total. Pumps 3 and 4 are standby pumps and Pumps 5 and 6 only run during extremely high flow events when the capacity of Pumps 1 through 4 is exceeded. Pumps 1 and 2, the plant s duty pumps, are clogging almost daily and require removal from service and manual cleaning every time they clog, prompting the City to investigate their replacement with WEMCO s Hidrostal pumps. The Hidrostal pump has a screw centrifugal impeller with an open channel that is less prone to clogging, and operates with good efficiency over the expected range of flows. Hidrostal pumps have been used at other Pacific Northwest wastewater pump stations at LOTT and Centralia where clogging was a problem that was solved by installation of WEMCO Hidrostal pumps. This section summarizes the evaluation of the existing influent pumps, replacement pump requirements, required pump system modifications, and estimated replacement cost Existing Influent Pump and Configuration The existing influent raw sewage Pumps 1 and 2 are Model B5414S nonclog, dry-pit, vertical centrifugal pumps manufactured by Fairbanks Morse. Existing pump data are shown in Tables 6-4 and 6-5. The motors are located on a separate level above the pumps, and there is a multiple-part vertical drive shaft designed and supplied by Johnson Power. The motors are 40-hp, 1,200-rpm motors, manufactured by U.S. Electrical Motors, and are powered by adjustable frequency drives located on the same structure level as the motors. The existing pump shop drawing is included in Appendix D-3. TABLE 6-4 Existing Raw Sewage Pumps No. 1 and No. 2 Data Parameter Manufacturer Model Size Suction diameter Discharge diameter Value Fairbanks Morse B5414S 8 inches 10 inches 8 inches 6-35

82 TABLE 6-5 Existing Raw Sewage Pumps No. 1 and No. 2 Performance Criteria Flow, gpm Total Discharge Head at Pump Discharge Flange, ft Efficiency, % Approx. Speed (rpm) 2, ,185 3, , Replacement Pump Requirements The Hidrostal pump model F10K-SS is recommended because it can meet the existing pump performance criteria for total dynamic head and flow. This model has a 13-¾-inch impeller diameter rated to pass a maximum solid sphere size of 4.75 inches. The pump is approximately 80 percent efficient at design performance conditions. The recommended Hidrostal pump drawing and pump curves are included in Appendix D Pumping System Modifications Required The existing pump shop drawings and proposed pump manufacturer drawings were compared to determine what modifications to the existing structure and piping system might be needed to install the Hidrostal pumps. These changes are shown on Figure 6-7 and include the following: 1) New pump base A new concrete pump base is required to fit the Hidrostal pump and maintain the existing suction fitting alignment. The pump would be aligned with the existing suction piping so that no modifications to the suction pipes are required. 2) Discharge piping modifications In addition to the manufacturer s drawings for the existing and proposed pumps, record drawings from the WWTP improvements completed in 2006 were used to determine the discharge pipe changes required. When the replacement pump is aligned at the appropriate suction location, the discharge is higher than the existing pump discharge. Therefore, the discharge piping must be reconfigured. The recommended discharge position is 180 degrees from the suction line, instead of the existing 270 degrees. The existing 10-inch x 8- inch reducing elbow would be removed since the new pump has a 10-inch discharge. Two new standard elbows and two horizontal spools are needed between each pump discharge and existing swing check valve. An additional horizontal spool is needed for the common discharge pipe located above the pumps. The vertical spool must also be shortened by 1 foot to accommodate the new pump height. In addition, two new pipe supports are required because the piping has been raised. 3) New or modified drive shaft The existing drive shaft is longer than necessary and has a different keyway geometry than that required by the new pump. The drive shaft will either need to be shortened and modified with a new coupling or a new 6-36

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85 drive shaft provided. Coordination between WEMCO, the pump manufacturer, and the shaft manufacturer, Johnson Power, is recommended. Additionally, a power transmission torsional and vibration analysis is recommended prior to installation. The Hidrostal pumps require 40 hp to operate at 1,300 rpm and achieve the design conditions. An electrical engineer conducted a preliminary review of the electrical requirements and believes the existing variable frequency drives can be oversped (beyond 60 Hz on 1,200 rpm motors) and have sufficient power capacity to accommodate the proposed pumps. A number of changes to the existing system are needed based on the results of this preliminary evaluation, and all modifications should be confirmed with detailed design prior to commencing the physical replacement Replacement Pump Installation Installation of the new pumps should be planned and sequenced to avoid disrupting plant operations. One possible sequence of work is as follows: 1. Confirm wetwell has sufficient storage volume to allow temporary shut off of influent pumps (and evaluate whether it is acceptable to bypass to the raw sewage equalization basin). 2. Turn off raw sewage pump motors No. 1 and No. 2 and close influent valves to both pumps. 3. Run standby pumps No. 3 and No. 4 start/stop during pump modifications. 4. Remove existing pumps No. 1 and No. 2, associated pump bases, and shafts. 5. Remove discharge piping that is no longer required or will be relocated and modified. 6. Install new pump bases, pumps, and shafts. 7. Install new and modified discharge piping. 8. Start up new raw sewage pumps No. 1 and No. 2. The estimated project cost for this work is $193,000 in May 2008 dollars and includes existing pump removal, new pump installation, new shafts, and piping modifications. A 30 percent contingency, contractor markups, and sales tax are also included in this estimate. This cost estimate is a Class 4 estimate with an expected accuracy of +50/-30 percent. 6-39

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87 CHAPTER 7 Financial Analysis This chapter estimates the potential change in residential sewer rates that would result from implementation of the projects described in Chapter 6. A schedule of costs for the improvements was developed with City staff based on the estimated time each improvement would need to be completed, and potential rate impacts were estimated on the basis of the cost schedule. Table 7-1 summarizes the improvements, their costs, and the assumed dates of completion. The projects were assumed to be completed in two phases beginning in 2010 and ending in All improvements needed in the next 5 years were assumed to be completed in All improvements needed in the 2020 to 2030 time period were assumed to be completed in Improvements needed after 2030 were assumed to be beyond the scope of this Facilities Plan. All costs shown in Table 7-1 are expressed in January 2007 dollars. The rate impacts described in the text are also expressed in January 2007 dollars. Appropriate adjustments will need to be made to these costs and rate impacts to account for inflation in future years. The costs and their timing in Table 7-1 represent a simplified cash flow and are intended to provide a general understanding of the costs for calculation of potential changes in residential sewer rates. The table shows that $14.3 million will be expended by 2010 and $22.1 million will be expended by Annual O&M costs do not increase substantially until 2025 when costs increase $373,000 for the expansion of the activated sludge process and new primary anaerobic digester. Changes in potential residential sewer rates were estimated using two assumptions for financing these improvements. Residential sewer rates are based on residential rates funding 57 percent of the cost of improvements and 8,550 residential accounts. This is the current percentage and number of accounts based on City records. The remainder is billed to commercial and industrial dischargers. The first assumed method of financing is the use of revenue bonds. Revenue bond financing is based on bonds issued for 20 years with an interest rate of 5 percent. Coverage on the bonds was assumed at 50 percent. These assumptions are based on information provided by City staff. Using revenue bond financing, residential sewer rates would increase $9.58 per month in 2010 and increase $26.43 per month in 2025, both expressed in January 2007 dollars. The other method of financing improvements is through the Ecology State Revolving Fund (SRF) loan program. In fiscal year 2008, the interest rate for loans of 5- to 20-year duration is 3.1 percent. No coverage is required, but the City must maintain a 1-year loan payment in reserve. With SRF loan financing, residential sewer rates would increase $5.40 per month in 2010 and increase $15.80 per month in Actual sewer rates should be developed in a formal rate study. The rates should be based on costs from more detailed engineering evaluations of the improvements. These engineering 7-1

88 evaluations should provide specific recommendations for facilities, more refined cost estimates, and a more detailed implementation schedule. TABLE 7-1 Estimated Costs of Improvements Used to Calculate Residential Rate Impacts Improvement New influent pumps $240,000 New fine screens $1,300,000 Expansion of activated sludge process $17,000,000 Anaerobic digestion Heating and mixing of secondary digester $740,000 Future primary digester $5,100,000 Drying bed expansion $1,100,000 Visual aesthetic improvements $3,600,000 Odor control improvements $4,200,000 Reclaimed water facilities (1.0 mgd) $2,700,000 Sludge management plan $150,000 Visual mitigation study $200,000 Odor control plan $100,000 Total Capital Costs $14,330,000 $22,100,000 Increased Annual O&M Expansion of activated sludge process $320,000 Anaerobic digestion Future primary digester $53,000 Increased O&M Costs $0 $373,000 All costs expressed in January 2007 dollars. 7-2

89 CHAPTER 8 Other 8.1 Water Quality Management Plan Conformance There is no formal Ecology water quality management plan in place for the Columbia River in the vicinity of the City of Wenatchee. Because of the relative health of this stretch of the Columbia River, Ecology has not closely studied this reach of the river and does not currently have plans to do so. Therefore, implementation of a water quality management plan or other additional water quality requirements for the study area is not anticipated in the foreseeable future. Should the City elect to make improvements to or expand their treatment process capacity, the resulting effluent is expected to meet or exceed current effluent quality and meet the plant s NPDES discharge permit obligations. 8.2 SEPA Environmental Checklist Appendix D contains a SEPA Environmental Checklist for the potential improvements to the WWTP and sludge drying beds. 8.3 SERP Compliance Federal law requires that states conduct environmental review of all State Water Pollution Control Revolving Fund (SRF) water pollution control facilities projects. Therefore, before the City is eligible to apply for a facilities design or construction loan, concurrence must be obtained from Ecology on environmental documents prepared and determinations issued by the City. Concurrence is obtained through the State Environmental Review Process (SERP), which helps ensure that public bodies select environmentally sound alternatives for the planning, design, construction, and implementation of the SRF water pollution control facilities projects. The SERP process is conducted during the development of the facilities plan. A facilities plan cannot be approved by Ecology until the SERP process is complete. To complete SERP, the City must comply with the State Environmental Policy Act (SEPA), the National Environmental Policy Act (NEPA), and other applicable environmental statutes, regulations, and executive orders. The City has prepared a SEPA checklist for this Facilities Plan (see Appendix E). A copy of the checklist and the threshold determination (it is assumed that a Determination of Non-significance [DNS] will be issued for the Facilities Plan) must be submitted to Ecology in order to have the plan approved. If the project complies with SERP, Ecology will concur with the preliminary DNS and will notify the City to issue the threshold determination. If Ecology does not concur with the determination, a notification letter will be sent to the City that directs the City to address any unresolved issues in order to complete SERP. Once the City has addressed the issues, SERP will be completed. 8-1

90 8.4 List of Required Permits For the proposed project, facilities plan approval and SERP compliance from Ecology will be required. Approval of Class A water reuse facilities from Ecology and the Washington Department of Health and Ecology will be required. Facilities plan amendments will be required to meet Ecology facilities plan requirements because this programmatic-level facilities plan does not contain required evaluation of alternatives and preliminary design information. Modification of the rated capacity of the existing WWTP will require modification of the NPDES permit. This can be done during one of the renewal processing conducted every 5 years based on Ecology approval of the Facilities Plan. For construction of the proposed facilities, the following permits could be required: For WWTP facilities, commercial building and grading permits from the City of Wenatchee For drying beds, grading permits from Chelan County Electrical permits from Department of Labor and Industries Plumbing permits from the Department of Health Water reclamation permit from Ecology and the Department of Health NPDES general construction permit from Ecology In addition, for the drying bed site, Chelan County would require an amendment to the existing conditional use permit, CUP Currently, this amendment process takes approximately 4 months to complete. No permits are required to be obtained from the U.S. Army Corps of Engineers or from Washington Department of Fish and Wildlife (WDFW) because the proposed project would not affect wetlands, streams, or rivers in the area. Extensive permits would be required for construction of a new WWTP, pump station, conveyance pipelines, and outfall. Evaluation of permits for a new WWTP is beyond the scope of this study. 8-2

91 CHAPTER 9 References CH2M HILL Wenatchee Wastewater Treatment Plant Improvements Engineering Report. Prepared for City of Wenatchee, Washington. October CH2M HILL Wenatchee Wastewater Treatment Plant Improvements Facility Plan. May CH2M HILL Final Facility Plan Amendment for Wenatchee Wastewater Treatment Plant Improvements. Prepared for City of Wenatchee, Washington. January City of Wenatchee Draft Wenatchee Comprehensive Sewer Plan. October Washington State Department of Ecology (Ecology) Criteria for Sewage Works Design. December Washington State Department of Ecology (Ecology) Stormwater Management Manual for Eastern Washington. 9-1