Christopher Mackin, Weston & Sampson, Worcester, MA
Frank Occhipinti, Weston & Sampson, Worcester, MA
ABSTRACT | In 2012, Fitchburg, Massachusetts, entered into a consent decree (CD) with the United States Department of Justice, EPA, and the Massachusetts Department of Environmental Protection (MassDEP). This was a result of the city failing to meet the combined sewer overflow (CSO) discharge requirements in its 2010 National Pollutant Discharge Elimination System (NPDES) permit (United States, Commonwealth of Massachusetts v. City of Fitchburg, 2012). Under the CD, the city must complete multiple sewer separation projects to eliminate CSO discharges by the end of 2030. Water quality standards for the United States and the MassDEP are regulated under the Federal Water Pollution Control Act (33 U.S.C. 1251 et seq), a.k.a. the Clean Water Act, and the Massachusetts Water Quality Standards (314 CMR 4.00). The CD specifies that the city must submit a Wastewater Management Plan (WMP) and a CSO Long-Term Control Plan (LTCP). The city developed its WMP and LTCP to identify the CSO controls necessary to comply with state and federal water quality standards and its 2010 and subsequent NPDES permits.
KEYWORDS | CSO mitigation, wet weather, regulatory compliance, SRF funding
The city of Fitchburg, one of over 700 combined sewer overflow (CSO) communities in the United States, is approximately 50 mi (80 km) northwest of Boston and has a population of over 40,000 residents (EPA 2024). During wet weather, the combined system experiences highly variable flow rates, significant inflow, debris buildup in the collection system, and untreated combined sewage (combined wastewater and stormwater) discharges to water bodies through relief points, known as CSO regulators, in the collection system. A combined system may also feature combined sewer maintenance holes (MHs) where transference between the wastewater and stormwater systems can occur during wet weather.
Construction of Fitchburg’s sewer system (circa 1890)
Before implementing any remedial measures to reduce or eliminate CSO discharges, the city operated an estimated 148 mi (238 km) wastewater collection system that consisted of over 127 mi (204 km) of sanitary sewers, 20 mi (32 km) of combined sewers, and 2.5 mi (4 km) of force mains. It also included 64 CSO regulators, 255 combination MHs, and three publicly owned pump stations. The wastewater collection system was constructed between 1890 and 2015 and includes sewers made of asbestos-cement, brick, cast iron, ductile iron, polyvinyl chloride (PVC), reinforced concrete, and vitrified clay. Wastewater from the entire city, as well as partial flow from the neighboring towns of Westminster and Lunenburg, is treated at the city-owned and operated Easterly Wastewater Treatment Facility (EWWTF), where treated effluent is discharged to the North Nashua River. When the treatment capacity is exceeded during wet weather events, the EWWTF uses a secondary system bypass to redirect flows to the North Nashua River after primary treatment.
Additionally, during wet weather events, the city’s CSO regulators discharge untreated combined sewage to the North Nashua River and other tributary water bodies. These discharges to waterbodies are regulated through the city’s National Pollutant Discharge Elimination System (NPDES) permit.
NPDES PERMIT
The city’s 2010 NPDES permit authorizes discharges from the EWWTF and CSOs to the North Nashua River and other tributary waterbodies. It also sets discharge limits for treated wastewater leaving the EWWTF and reporting requirements for compliance. The permit specifies a monthly average flow limit of 12.4 mgd (46.9 ML/d) that can be discharged into the North Nashua River. Prior to any improvements to the EWWTF, during wet weather events when flow rates exceeded 15 mgd (57 ML/d), the EWWTF activated its secondary system bypass. Historically, flows exceeding the capacity of the treatment facility were not treated to the level that met water quality standards, resulting in NPDES permit violations.
The city’s NPDES permit also requires that combination MHs showing signs of transference must have storm and sanitary sewer separation completed within two years of the transference date.
HISTORIC PROJECTS
Fitchburg initially began investigating sewer separation to remove combined sewers in 1995. In 1999, the city reported 20 mi (32.2 km) of combined sewers and 58 CSO regulators. A CSO Master Plan was developed in 1999 to address the collection system, main trunk line, and treatment plants. In 2002, the city created a Combined Sewer System (CSS) Separation Program that prioritized areas for separation based on the largest CSOs. Since 1999, the city has been performing sewer separation and rehabilitation projects to reduce the number of combined sewers.
Between 1999 and 2018, the city completed several sewer system evaluation survey (SSES) and investigation projects, resulting in the successful inspection of 88 percent of the sanitary and combined sewers and 43 percent of the sewer MHs in the city, as summarized in Table 1. During this time, the city conducted four major sewer separation projects and multiple sewer rehabilitation projects to remove infiltration and inflow (I/I) from the wastewater collection system, as summarized in Table 2.
Between 1999 and 2018, sewer separation and rehabilitation projects successfully removed over 10 mi (16 km) of combined sewers, closed 47 CSO regulators, and significantly reduced CSO discharge volumes to the North Nashua River.
Table 1. Historic sanitary sewer evaluation surveys and investigation projects
Table 2. Historic sewer separation and rehabilitation projects
EWWTF Upgrades
Table 3. Treatment capacity improvements from secondary system upgrades
Owing to violations of the city’s 2010 NPDES permit, in 2012 the city entered into a consent decree (CD) with the United States Department of Justice, EPA, and the Massachusetts Department of Environmental Protection (MassDEP) that required the city to conduct upgrades to the EWWTF to increase its capacity. In 2019, the city completed a chemically enhanced primary treatment (CEPT) upgrade to the EWWTF, and in 2020, it completed a secondary system upgrade (SSU) project. These improvements increased facility capacity, as shown in Table 3.
Following the SSU, it was estimated the EWWTF could treat up to 40 mgd (151.4 ML/d) of wastewater during the winter, 32 mgd (121.1 ML/d) during the summer, and 20 mgd (75.7 ML/d) in May. Sewer separation is anticipated to reduce peak wet-weather flow rates to a rate that will receive full wastewater treatment.
Wastewater Management Plan
As required by the CD, the city began developing a Wastewater Management Plan (WMP) and CSO Long-Term Control Plan (LTCP) for submittal to EPA and MassDEP. The purpose of the WMP was to develop a plan of projects that would enable the city to comply with state and federal water quality standards by a 2030 deadline. Municipalities with combined sewers must create LTCPs to facilitate the removal of untreated CSO discharges to surface waterbodies. Per the CD, accomplishments needed to meet conditions in the NPDES permit by the deadline include aggressively phased sewer separation, reduction toward elimination of CSO discharges, diligent I/I detection and mitigation, and regular reporting of progress and scheduling adjustments demonstrating effective efforts to meet CD requirements. Additional work required by the CD included investigating and designing combined sewer separation projects and treatment facility upgrades to meet permitted standards.
In addition to the initial WMP submission, the city was required to submit two WMP update reports in December 2020 and December 2023.
Figure 1 CSO regulator layout
The city submitted the WMP Phase I Report to EPA and MassDEP in May 2019. The report discussed improvements to the city’s wastewater collection system between 1999 and 2019 and ongoing improvements to the EWWTF. In addition, the WMP included a CSO LTCP that developed a schedule to meet permitted CSO conditions. The LTCP identified the CSO controls necessary to comply with state and federal water quality standards and the city’s NPDES permit requirements, establishing the city’s plan to mitigate CSO discharges to the North Nashua River and other tributary water bodies. MassDEP requires that municipalities must perform sewer separation as the primary CSO control method, unless proven to have “substantial and widespread social and economic impacts.” Following an economic analysis, the city developed an aggressive sewer separation project schedule to complete CSO mitigation.
The WMP Phase II Report was submitted in December 2020. The report discussed infrastructure studies and improvements that the city had completed between 2019 and 2020 and reviewed preliminary performance results from the EWWTF’s secondary system upgrade. The Phase II Report also identified the city’s anticipated schedule for sewer separation-related projects for the next three years and updated the remaining schedule to meet CSO conditions in the CD.
The WMP Phase III Report was submitted in December 2023. The report discussed studies and improvements completed between 2020 and 2023, listed the work planned for the next three-year period, assessed the abatement anticipated, and again updated the anticipated remaining schedule to meet CSO conditions by the CD deadline. The city is persistently following the combined sewer separation program schedule from the Phase I, Phase II, and Phase III reports.
Because of the anticipated issuance of an updated NPDES permit, the city will provide a Supplemental WMP Phase III Report in December 2024. The supplemental report will describe improvements to the EWWTF, as well as the completion of recent CSO and I/I mitigation projects, and will recommend additional EWWTF upgrades (if needed) to meet the updated NPDES permit.
INFRASTRUCTURE IMPROVEMENT PROJECTS (2018 to present)
One of Fitchburg’s CSO regulators.
During development of the WMP Phase I and CSO LTCP, the city’s remaining combined sewer system was primarily concentrated near the city center. In total, 8.4 mi (13.5 km) of combined sewers and 11 CSO regulators remained active in the city in 2019. After analyzing the WMP and CSO LTCP, the city adjusted its capital improvement plan (CIP) to prioritize sewer separation projects for CSO control.
The sewer separation projects were prioritized based on the number of historical overflow events and volumes and on the locations of the CSO regulators. Since most of the CSO regulators are upstream of the largest regulator (CSO 064) as shown in Figure 1, sewer separation of the entire tributary area is required prior to CSO 064 closure. As a result, that closure was identified as the last of the four sewer separation projects to be conducted, completing closure of all the city’s remaining CSO regulators.
While the WMP and CSO LTCP strategically targeted the combined sewer system, the city also conducted investigation and rehabilitation projects in its wastewater collection system.
SSES Phase IV Interceptor Evaluation
In 2019, the city conducted the fourth phase of its SSES. This included multi-sensor inspections on approximately 31,144 LF (9,500 m) of interceptor sewers ranging in diameter from 18 in. (46 cm) to 48 in. (122 cm), including the wastewater interceptor. CCTV, laser, sonar, and hydrogen sulfide inspections were part of this work. The city also conducted 138 MH inspections, smoke tested 17,500 LF (5.3 km) of sewers, and inspected 60 buildings, costing $484,000.
Through the inspections and smoke/dye testing, the city identified five sump pumps and five catch basins connected to the sanitary sewer system. It then prioritized rehabilitation based on critical defects identified during these inspections. An estimated $14.7 million in sewer pipe, MH, and inflow rehabilitation was recommended.
Siphon/Various Sewers Heavy Cleaning and Inspection
In June 2020, the city started its siphon and sewer heavy cleaning and inspection project. The goal was to clean and inspect the city’s five siphons as well as the sewers upstream and downstream of each siphon, along with sewers previously identified as containing heavy debris. The heavy cleaning and inspections were completed in October 2020.
During the cleaning and inspection, an estimated 284 yd3 (217 m3) of debris was removed from the wastewater collection system. A condition assessment was also performed for each siphon barrel and sewer inspected. An estimated $881,000 of high-priority sewer rehabilitation was subsequently recommended. The city spent over $450,000 for the investigation and cleaning performed in this project.
Elm Street Sewer Repair
During the siphon cleaning and inspection project, significant pipe degradation was observed in two 26 by 39 in. (66 by 99 cm) brick sewers on Elm Street. The pipes were missing significant brickwork near the invert and risked collapse. The city replaced the brick sewers with 36 in. (91 cm) PVC pipe. These repairs were completed in September 2020.
CSO 007, 011, 039, 048 Separation and Rehabilitation
In August 2018, the city began investigating and designing the CSO 007, 011, 039, 048 separation and rehabilitation project, aiming to close CSO regulators 007, 039, and 048. The investigation and design phases were completed in July 2020, with construction beginning that November and finishing in July 2023. The post-construction monitoring phase was completed in the summer of 2024. Through this project, the city closed three CSO regulators that had contributed an estimated 20.8 MG (78.7 ML) of CSO discharges to the North Nashua River between 2012 and 2020. The construction separated approximately 4,800 LF (1,463 m) of combined sewers through the installation of 4,850 LF (1,478 m) of new PVC sewers and 2,700 LF (823 m) of new HDPE drains, and separated 19 combination MHs. In addition, approximately 2,100 LF (640 m) of sewers were replaced in areas already separated and 20,000 LF (6,096 m) of sewers were rehabilitated across the project area. The city had previously closed CSO 011, but it still had combined sewers remaining upstream. Fitchburg spent $725,850 on the investigation and design and $9.6 million on construction. Drains in the project area were designed to function during an estimated 2070 10-year, 24-hour storm event.
Combination Maintenance Hole Separation Program
The city’s NPDES permit requires that separation of combination MHs is required if there are signs of transference between the wastewater and stormwater collection systems. In 2019, the city began combination MH inspections and designed the separation of 150 combination MHs with known signs of transference. The city allocates funding to perform separations each year until all combination MHs are separated and is actively separating combination MHs throughout the city. Fitchburg also began integrating the combination MH separation program with combined sewer separation projects to achieve an accelerated, cost-effective, and comprehensive separation of combination MHs upstream of combined sewers. From 2016 through December 2023, the city had closed 155 of the 255 combination MHs, with 100 combination MHs remaining. The city will continue to integrate the combination MH separation program with the remaining combined sewer separation projects.
Construction of green infrastructure during the CSO 010 project, in this case a bioretention cell
CSO 010, 032, 045, 083 Separation/ Rehabilitation
In July 2021, the city began investigating and designing the CSO 010, 032, 045, 083 separation and rehabilitation project, aiming to close CSO regulators 010, 032, 045, and 083, (photo previous page). The project includes the separation of approximately 27,600 LF (8,230 m) of combined sewers through the installation of 10,850 LF (3,300 m) of new PVC sewers, 1,450 LF (442 m) of new PVC drains, and 42,350 LF (12,900 m) of new HDPE drains. In addition, approximately 48,100 LF (14,660 m) of sewers were recommended for trenchless rehabilitation to repair structural defects and reduce I/I in the project area.
Drains in the project area were designed to function during the 2070 10-year, 24-hour storm event. The city received funding for this in fiscal years 2023 and 2024 through the Massachusetts Municipal Vulnerability Preparedness (MVP) Program to design related green infrastructure improvements within the project area.
The size of the area resulted in three phases of construction for the separation and rehabilitation: CSO 010, CSO 032/045, and CSO 045/083. The CSO 010 construction project was advertised for public bid in March 2023, and construction commenced that June. Construction is estimated to be completed by the end of this year, with post-construction monitoring and sampling concluding about one year later.
The CSO 032/045 construction project was advertised for public bid in June of this year with construction expected to commence in August, and the CSO 045/083 construction project is expected to be advertised for public bid in March 2025 with construction expected to commence that June. Construction of the CSO 032/045 and CSO 045/083 projects is estimated to be completed by the end of 2026 and the end of 2027, respectively, with post-construction monitoring and sampling in each phase concluding one year after construction completion.
Capacity, Management, Operation, and Maintenance Program
By early 2024, the city had inspected about 94 percent of its sewers and 57 percent of its MHs. Since the remaining sewers requiring inspection are beyond in-house capabilities, the city began re-inspecting sewers in the collection system, with about 19 percent now having been inspected. The remaining sewers that have not been inspected will be inspected through future sewer separation and rehabilitation projects.
FUNDING
Fitchburg has invested $82 million in the wastewater collection system and wastewater treatment facility improvements to comply with the CD. The city anticipates spending an additional $92 million on infrastructure improvements to close all remaining CSO regulators by 2030 through the separation of all remaining combined sewers, and additional funding sources were considered to help finance the required improvements.
Water and Sewer Rate Study
In 2023, the city performed a water and sewer rate study to determine the required rate structure for funding infrastructure projects enforceable under the city’s CD while also considering the affordability of any necessary rate increases. Understanding and implementing the most appropriate rate structure to fund the required improvements was critical to the long-term financial sustainability and viability of the city’s water and sewer funds. Workshops were held with the city’s DPW and Water, Sewer, and Financial departments to review the financial and billing data for water and sewer services. The city also developed comprehensive water and sewer financial plans and rate structures.
State Revolving Fund Loan Program for Sewer Separation
The city expects most of the funding for the remaining infrastructure improvements will come from the MassDEP’s State Revolving Fund (SRF) Loan Program. Many of the previous infrastructure improvement projects required under the CD were also funded through this program, including the city’s ongoing CSO 010 separation and rehabilitation construction project. The city has secured SRF funding for the upcoming CSO 032/045 separation and rehabilitation construction project and also intends to fund the future CSO 045/083 project through this program.
Municipal Vulnerability Preparedness Program
The city is committed to increasing the resiliency of its stormwater system for future conditions affected by climate change. As part of MVP funding requirements, stormwater improvements that are part of the city’s sewer separation and rehabilitation projects will be designed to function during the projected 2070 10-year, 24-hour storm. MVP funding was targeted as a method of funding for stormwater improvements recommended in the CSO 010, 032, 045, 083 separation and rehabilitation project. The city received MVP funding for this project and has identified five locations for green infrastructure as part of the CSO 010 project. The city also intends to include 12 locations for green infrastructure between the CSO 032/045 and 045/083 projects.
The city is planning to apply for additional MVP funding for future sewer separation projects. This will coincide with its goal of implementing green infrastructure, wherever applicable and feasible, as identified in the CD.
Figure 2. Proposed sewer separation schedule
Capital Improvement Plan Update
In the next three years, Fitchburg will have three major combined sewer separation projects underway, each in a different stage. Four additional remaining sewer separation projects will close all the city’s remaining CSO regulators. See Figure 2 for the current sewer separation schedule. The city also plans to separate combination MHs as funding becomes available.
CONCLUSION and SUMMARY
Fitchburg’s Easterly wastewater treatment facility
The city continues to address approximately 7.4 mi (11.9 km) of combined sewer, eight CSO regulators, and 100 combination MHs remaining in its wastewater collection system. Most of its upcoming capital improvement projects will focus on CSO mitigation through sewer separation, along with additional I/I mitigation through combination MH separations and sewer rehabilitation. In addition to the elimination of CSOs from the wastewater collection system through the combined sewer separation, and I/I mitigation, the city anticipates a reduction in total and peak wastewater flows conveyed to the EWWTF during storm events. This will also provide significant improvements to water quality in the North Nashua River.
The city has invested over $82 million in the wastewater collection system and wastewater treatment facility improvements to comply with the CD. It expects to spend an additional $92 million over the next six years to continue with sewer separation and rehabilitation projects to close the remaining eight CSO regulators and meet the CD deadline of 2030.
For communities undertaking a large CSO separation or other project similar to Fitchburg’s, the following is recommended:
- Develop a plan. Combined sewer systems should be evaluated holistically in the long term, factoring CSO mitigation in with other infrastructure improvements.
- Assess vulnerable conditions. CSO communities with highly variable flow rates have different vulnerabilities than other communities and these should be considered when planning long-term improvements.
- Develop an annual investigation and operation and maintenance (O&M) program. Combined sewer systems introduce large amounts of grit and debris into the wastewater collection system, requiring a robust investigation and O&M program.
- Consider your wastewater and stormwater system’s resiliency as part of the proposed improvements.
- Take it one step at a time.
ACKNOWLEDGMENTS
The authors acknowledge Nick Erickson, PE (commissioner of public works and city engineer), Mark McNamara (deputy commissioner and acting plant superintendent of wastewater), Ken Dupont (sewer system manager), and Jeff Hillman, PE (superintendent of streets and civil engineer) from the Fitchburg DPW for their support of the ongoing sewer separation projects in the city.
REFERENCES
United States Environmental Protection Agency. Where Combined Sewer Overflow Outfalls Are Located | US EPA. Last updated on June 10, 2024, Accessed July 29, 2024.
ABOUT THE AUTHORS
- Christopher Mackin is a senior project manager at Weston & Sampson in Worcester, Massachusetts. He has over 20 years of experience in wastewater and stormwater collection systems, stormwater design, and site and civil engineering. He earned his Bachelor of Science in Civil Engineering from Worcester Polytechnic Institute (WPI).
- Frank Occhipinti is the Worcester regional manager for Weston & Sampson in Worcester, Massachusetts. He has more than 25 years of experience specializing in the planning, design, and construction of sanitary and storm sewer projects, as well as I/I analysis and sewer rehabilitation. He earned his Bachelor of Science in Civil Engineering Technology from the Wentworth Institute of Technology.
Published in NEWEA, September 2024.