Executive Summary – Consent Decree
The sewer system in Nashville dates back to the late 1800s and originally consisted of a combined sewer system, later transitioning to separate sanitary and storm sewers. A combined sewer system consists of a single set of pipes that conveys both sanitary sewage and storm water. Combined sewer systems were common in cities that developed in the 19th century to address public health problems caused by lack of proper sanitation. Since there were no facilities for treating wastewater in that era, sewage and storm water were both discharged directly to the rivers and streams. The treatment of wastewater began in the 20th century when interceptors were constructed to convey sanitary sewage along with storm water to treatment plants to improve water quality. Wastewater treatment plants have limitations, however, to the volume of flow that can be effectively treated during rainfall events. Intense rainfall often leads to flows of stormwater in the combined sewer system that exceeds treatment plant capacity. These high flows of primarily stormwater are discharged without treatment and referred to as combined sewer overflows or CSOs. Separate sanitary sewers are intended to convey only sanitary sewage, but the piping systems deteriorate over time allowing rainwater to leak into the lines. During extreme rainfall events, the volume of rainwater entering these older sewers can overwhelm the capacity of the system, leading to sanitary sewer overflows (SSOs). Metro Water Services began an aggressive program in 1990 to reduce the number of CSOs and SSOs, making tremendous progress toward improving water quality in the Cumberland River and its major tributaries. However, despite these improvements, a significant number of overflows still remained, prompting state and federal regulatory agencies to approach Metro in 2007 about the need for additional work within the sewer system. In March 2009, a consent decree between the United States of America, the State of Tennessee, and the Metropolitan Government of Nashville and Davidson County was approved and entered with the United States District Court for the Middle District of Tennessee. The consent decree was filed on behalf of the United States Environmental Protection Agency (EPA) and the Tennessee Department of Environment and Conservation (TDEC), and it requires Metro to use its best efforts to achieve the following goals: 1. Full compliance with National Pollutant Discharge Elimination System (NPDES) permits, the Clean Water Act, the Tennessee Water Quality Control Act, and their regulations. 2. Elimination of sanitary sewer overflows (SSOs). 3. Compliance with EPA’s combined sewer overflow (CSO) Control Policy.The schedule for the Consent Decree was amended in August 2010 to provide additional time due to the impacts of the May 2010 flood. The amended schedule includes the following requirements: 2 ½ years to develop a Corrective Action Plan/Engineering Report (CAP/ER) to address conditions causing overflows in the separate sanitary sewer system with the goal of eliminating SSOs 2 ½ years to develop an updated Long Term Control Plan (LTCP) to mitigate overflows from the combined sewer system and reduce water quality impacts to the Cumberland River 11 years after approval of each of these documents to complete the recommended improvements The Consent Decree also includes provisions for civil penalties for past violations and stipulated penalties for violations that may occur in the future. In lieu of the full civil penalty, Metro agreed to conduct and has completed Supplemental Environmental Projects to improve public health and the environment. At a total estimated cost of $1.0–1.5 billion, the Clean Water Nashville program represents a major investment in overflow abatement for the community and provides the following benefits: Renews and improves aging infrastructure Enhances the environment for Nashville Improves water quality in the Cumberland River and its tributary watersheds in Metro Davidson County Provides major engineering and construction projects to boost the local economy Executive summaries for the Corrective Action Plan/Engineering Report and the Long Term Control Plan follow, along with Figure ES‐2, which displays the recommended projects included in both reports.
Corrective Action Plan/Engineering Report
This report presents the approach to characterize Metro’s sanitary sewer system and to evaluate potential alternatives for improvements to address hydraulic limitations. The major steps of this evaluation are described below: Extensive rainfall and flow monitoring data was collected through the study area to characterize base wastewater flows, groundwater infiltration, and rainfall‐derived infiltration and inflow (RDII). The primary focus of the analysis used data collected from February through April 2008; however, data collected from 2004 through 2010 was utilized to supplement this analysis. Data collection is described in Section 2 of this report, and the analysis of this data is included in Section 3. Hydraulic models of the sanitary sewer system were developed using Mike Urban software and EPA’s Stormwater Management Model (SWMM) version 5.0. The models include most gravity sewers 10‐inches or greater in diameter; additional smaller diameter sewers were also included for connectivity and to model areas of concern. For the purposes of this analysis, the collection systems serving each wastewater treatment plant service area were modeledseparately, resulting in three models representing the Dry Creek, Whites Creek, and Central systems respectively. Model development is described in Section 4 of the report. Using the collected rainfall and flow monitoring data, the hydraulic models were first calibrated to dry weather flow conditions. The second step of model calibration involved comparing model‐predicted RDII flows to those measured in the system as part of the flow monitoring program. Following completion of the calibration step, the models were compared to a second set of data for verification purposes. The model calibration steps result in models that meet the calibration goals and are acceptable for use in evaluating capacity under various scenarios to resolve capacity limitations. The calibration process is described in Section 4.3 of the report. To evaluate the need for improvements to the system, design conditions were applied to the models. This includes dormant season dry weather flows as well as the 2‐year, 24‐hour dormant season design storm. This storm event includes a peak intensity of 0.97 inches per hour and a 24‐hour volume of 3.15 inches. Details of the development of this design storm are provided in Section 3.4 of the report. For SSOs listed in the CD and other model‐predicted, field‐verified overflows, the models were used to evaluate potential improvements to alleviate SSOs under design conditions. Improvements considered included pump station and pipeline improvements to increase conveyance capacity, storage to equalize peak flows, and sewer rehabilitation to reduce the amount of RDII entering the system. The alternatives analysis for the Dry Creek, Whites Creek and Central service areas are described in Sections 6, 7, and 8 of the report, respectively. Of the potential improvements capable of alleviating SSOs under design storm conditions, the project team evaluated each improvement considering costs, constructability, operations, and other factors to select the proposed improvement. This discussion is also included in Sections 6, 7, and 8 for the Dry Creek, Whites Creek, and Central service areas, respectively. Proposed projects were prioritized considering the frequency and severity (volume) of overflow being addressed, proximity of the SSO to public areas and 303d‐listed streams for E. coli, and project complexity, such as the need to acquire property, project sequencing, or estimated construction durations. As a result of this process, Metro has identified multiple projects that will be completed as this CAP/ER is implemented. These projects are listed in Table ES‐1. This table is also presented in Section 9 of the report and includes projects previously identified by Metro that will contribute to the reduction of SSOs within the system. Table ES‐1 also provides the preliminary, planning‐level schedule for the proposed projects. As shown in the schedule, Metro intends to complete all CAP/ER projects within the eleven year timeframe provided. The project start shown represents the start of project activities, including planning, land or right‐of‐ way acquisition, etc. The project end indicates the target completion date for the referenced project. All dates for proposed projects assume approval of the CAP/ER no later than January 1, 2012. If approval is received after that time, the schedule will be shifted forward to account for that delay.
Executive Summary Executive Summary
Table ES‐1 – CAP/ER Implementation Plan and Schedule
Project Name Service Area Project Start (Fiscal Year) Project End (Fiscal Year) Dry Creek WWTP Optimization Dry Creek 2004 2009 Smith Springs Equalization Storage Central 2006 2006 Barker Road / Omohundro Equalization Storage Phase I Central 2006 2010 West Park Equalization Storage Phase I Whites Creek 2006 2011 Mill Creek 36” Trunk Sewer System Rehabilitation Central 2008 2012 Whites Creek WWTP Disinfection & Optimization Whites Creek 2009 2013 Whites Creek Pump Station Improvements Whites Creek 2010 2014 Dodson Chapel Equalization Storage Central 2011 2015 Holiday Travel Park Gravity Conversion Central 2011 2013 Lakewood Rehabilitation Dry Creek 2011 2018 28th Avenue Rehabilitation Central 2012 2022 Cowan / Riverside Drive Rehabilitation Central 2012 2018 Dodson Chapel Pipe Improvements Central 2012 2017 Mill Creek / Opryland Equalization Storage Phase II Central 2012 2016 Rockwood Conveyance Improvement Central 2012 2017 Shelby Park Rehabilitation Central 2012 2022 Smith Springs Rehabilitation Central 2012 2021 Neely's Bend Rehabilitation Dry Creek 2012 2014 Davidson Branch Equalization Storage Whites Creek 2012 2017 Highway 100 / Tyne Boulevard Pipe Improvements Whites Creek 2012 2018 Joelton Rehabilitation Whites Creek 2012 2015 West Park Equalization Storage Phase II Whites Creek 2012 2015 Dry Creek Pipe Improvements Dry Creek 2013 2017 Gibson Creek Rehabilitation Dry Creek 2013 2016 Vandiver Pump Station Upgrades Dry Creek 2013 2017 622 Davidson Rehabilitation Whites Creek 2013 2016 Brick Church Pike Equalization Storage Whites Creek 2013 2017 Brick Church Pike Pipe Improvements Whites Creek 2013 2017 Langford Farms Rehabilitation Central 2014 2017 Mill Creek Trunk Improvements Central 2014 2022 Berwick Trail Pipe Improvements Dry Creek 2014 2020 Berwick Trail Pump Station Upgrades Dry Creek 2014 2020 Gibson Creek Equalization Storage Dry Creek 2014 2019 Hidden Acres Pump Station Upgrades Dry Creek 2014 2020 Loves Branch Pump Station Upgrades Dry Creek 2014 2020 Neely's Bend Pump Station Upgrades Dry Creek 2014 2020 Hurricane Creek Pipe Improvements Central 2015 2020 Mill Creek / Opryland Equalization Storage Phase III Central 2015 2022 Notes: (1) Fiscal year is defined as the period starting on July 1 and ending on June 30 of the year shown.
Executive Summary Executive Summary
Table ES‐1 – CAP/ER Implementation Plan and Schedule (continued)
Project Name Service Area Project Start
(Fiscal Year) Project End (Fiscal Year) GC14 Trunk Improvements Dry Creek 2015 2019 Madison Heights / Rainbow Terrace Rehabilitation Dry Creek 2015 2017 West Park Equalization Storage Phase III Whites Creek 2015 2019 Cleece Ferry Rehabilitation Whites Creek 2017 2022 Cowan Street Pipe Improvements Central 2018 2023 Riverside Drive Pump Station Upgrades Central 2018 2022 Henry Ford Drive Pipe Improvements Whites Creek 2018 2023 River Drive Rehabilitation Whites Creek 2018 2021 Cowan Street Pump Station Upgrades Central 2019 2022 GL01 Rehabilitation Central 2019 2022 Notes: (1) Fiscal year is defined as the period starting on July 1 and ending on June 30 of the year shown. (2) Phasing is only shown for multiple storage tank locations. Other projects may be separated into phases as the project design progresses.
Long Term Control Plan
The Long Term Control Plan Update presents a characterization of the MWS combined sewer system and the recommended improvements to reduce the occurrence and impact of combined sewer overflows (CSOs) on the Cumberland River. MWS followed a rigorous engineering, quantitative, and scientific process for identifying and evaluating alternatives to control CSOs. Financial considerations and engineering analyses were also used to develop the recommended improvements, in conjunction with four key objectives that were established early in the planning process: Improve the water quality of the Cumberland River by reducing impacts from combined sewer overflows. Provide a level of CSO control that results in improvements in water quality that are consistent with the community’s needs and use of the Cumberland River. Align investment in CSO controls to be commensurate with the contribution of CSOs to water quality standards violations relative to other sources. Consider the impact of the overall program cost on the ratepayers in the current economic climate. These goals and objectives were developed based on feedback provided by representatives from MWS, local government, and the community through a Public Engagement Campaign developed to solicit input from affected stakeholders. Prior Efforts to Control CSOs Attention and focus on CSOs over the past 23 years has resulted in significant improvements in the combined sewer system and has aided in improving the water quality of the Cumberland River. When the Overflow Abatement Program began in 1990, there were a total of 32 CSO discharge points in downtown Nashville. With an expenditure of over $265 million on improvements, significant reductions in CSO discharges have been attained through the Overflow Abatement Program. These improvements have eliminated 24 CSO discharge sites and greatly reduced the total volume of untreated discharges into the Cumberland River on an annual basis. Currently, only eight CSO locations remain as depicted in Figure ES‐1. Characterization of CSO Discharges Hydraulic models of the combined sewer system were developed to determine the relationship between rainfall events and CSO discharges. The hydraulic models were calibrated using an extensive array of flow monitors and a network of 16 Metro rainfall gauges. The benefits of reductions in CSO discharges were assessed on an annual basis. To accomplish this task, precipitation records for the past 54 years were examined to select a year reflective of average conditions for rainfall volume, intensity, duration and number of events. The year 1995 was selected to represent the typical year for rainfall in Nashville, and rainfall data for that year were utilized for hydraulic modeling of the combined sewer system. Additionally, modeling was conducted to assess the water quality impact on the Cumberland Riverstreams and urban runoff. Water quality modeling focused on two sensitive areas, Riverfront Park and Cleece Ferry. There are currently four CSO discharge sites upstream of Riverfront Park, and four additional CSO discharge sites upstream of Cleece Ferry. Figure ES ‐ 1: Eight MWS CSO Locations in 2010 Summary of Recommended Improvements to CSO Outfalls Extensive hydraulic modeling was conducted to analyze the effect of various alternatives for each of the areas within the combined sewer system. These alternatives typically consist of reduction in flow by removing a portion of the storm water from the system, conveyance improvements to transport additional flow, or storage facilities to temporarily store excess flow during rainfall events. The hydraulic modeling estimates the number of annual overflows for each alternative utilizing the rainfall data for the typical precipitation year. The recommended improvements and the typical year overflow frequency for each of the eight CSO discharge sites are summarized in Table ES‐2. 2010
Table ES – 2 ‐ Summary of Major Long Term Control Plan Projects CSO Site Overflow Frequency for Typical Year Recommended Project Type Boscobel 0 storage tank Benedict & Crutcher 2 storage tank Driftwood 0 additional volume for existing storage tank
Broadway N/A eliminate by conveyance improvement
Washington 11 conveyance improvement and system storage
Kerrigan 9 conveyance improvement and storage tank
Van Buren N/A eliminate by conveyance improvement
Schrader 2 storage tank Benefits of Recommended Plan MWS has put forth an aggressive CSO control plan that is consistent with its long history of improving the water quality of the Cumberland River. The recommended improvements under the LTCP will provide the following benefits: Incorporate green infrastructure and low impact development techniques to reduce storm water loading to CSS Eliminate two CSO overflow sites Reduce typical year discharge frequency for four of the remaining CSO sites to two or less per year Reduce typical year discharge frequency at the two largest CSO sites from 20‐50 times/year to 9‐11 times/year Reduce annual CSO volume for a typical year by 53% from current levels Achieve near zero hours of water quality standard exceedance from CSOs at Riverfront Park in a typical year Reduce water quality standard exceedance from CSOs at Cleece Ferry to approximately 29 hours (or less than 1% of the hours) in a typical year Select alternatives that limit neighborhood impact from construction and minimize property acquisition Address public concerns of affordability to ratepayers in difficult economic times Provide a level of water quality attainment in the Cumberland River consistent with the community’s uses and needs The projects recommended under the LTCP, along with planned starting and ending dates for the 11‐year implementation period, are listed in Table ES‐3.
Table ES‐3 ‐ Planned Schedule for Combined Sewer System Improvements Project Name Projected MWS FY* Start Projected MWS FY* End Affected CSO
Broadway Improvements U/C 2012 Broadway
Washington CSO Facility Improvements U/C 2012 Washington
Van Buren Improvements U/C 2012 Van Buren
Driftwood EQ Expansion 2012 2015 Driftwood CWWTP Optimization + EQ Conversion (5mgal) 2013 2016 Kerrigan Kerrigan Weir Dynamic Addition 2013 2016 Kerrigan Apex Sewer Corrections 2013 2016 Washington Parthenon Area Improvements 2013 2016 Kerrigan Green Improvements (Annual) 2012 2023 Various CWWTP EQ Addition Ph 1 (13 mgal) 2013 2017 Kerrigan CWWTP Pumps/EQ Grit Equipment 2014 2018 Kerrigan CWWTP EQ Expansion Ph 2 2016 2019 Kerrigan Benedict & Crutcher PS/EQ 2017 2020 Benedict & Crutcher Boscobel PS/FM/EQ 2018 2021 Boscobel FAT Access 2018 2021 Van Buren Schrader PS/EQ 2018 2022 Schrader CWWTP EQ Expansion Ph 3 2019 2023 Kerrigan Trash Trap Replacement 2020 2023 Kerrigan CSS + FAT Rehab 2020 2023 Various Notes: *FY is Metro fiscal year starting July 1 and ending June 30 of the year shown. U/C is under construction.
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