Overview of Combined Sewer Overflow
Following heavy rainstorms, such as those we’ve had in July and September 2023, water running off of roads and lawns makes its way either into a storm drain, where it is conveyed through pipes to a waterbody, or will go to a treatment plant before being discharged into a river. This water is know as “stormwater,” which refers to the water that runs off of the land into the drainage system or surface waters during precipitation events, instead of soaking into the ground.
In many older cities, the pipes that transport stormwater and the pipes that transport sewage from your house are one and the same. When populations were much smaller and water treatment was nonexistent, it was most efficient to have just one pipe for everything, which would ultimately discharge (untreated) into the river. Thankfully, following the passage of the Clean Water Act, these pipes were diverted to treatment plants, where sewage, and sometimes stormwater, are treated before discharging the liquids (also known as effluent) back into the river.
However, as populations in cities and towns expanded, so has the demand on this combined stormwater and sewer infrastructure. Today, in areas where sewage and stormwater pipes are combined, intense rainfall or snowmelt can be too great of a volume for the pipes to convey and for the treatment plants to process. As a result, the mixture of stormwater and sewage “bypass” treatment and are discharged directly into the river. This discharge is called a Combined Sewer Overflow, or CSO.
The Massachusetts and Connecticut portion of the Connecticut River is impacted by five remaining CSO communities, all of which have been working to reduce CSO discharges for decades. However, the cost of this work is enormous, which presents significant challenges, especially in cities and towns where increasing water and sewer rates (which is how much of this work is paid for) creates issues of affordability for residents.
With the increase in intensity and frequency of floods, as we experienced in July and September 2023, it is critical that we support the work of cities and towns to reduce and eliminate CSOs. Below is a brief description of the ongoing work of each CSO community as well as resources for further reading. The Connecticut River Clean-up Committee, hosted by the Pioneer Valley Planning Commission, has been pivotal in securing funding for CSO abatement in the three largest CSO communities in Massachusetts.
Each of us can support the work of wastewater departments and commissions by reducing our own water use at home. When affordable, water efficient appliances lessen the burden on wastewater systems. If you have a lawn or hard surfaces at your home, consider installing ‘green infrastructure’ to help reduce the amount of stormwater entering the system.
MassDEP Map of CSOs
CSO Data Portal
The Clean Water Project
CT DEEP CSO Bypass map
Bringing Green Infrastructure to Your Community
The Metropolitan District (MDC) provides water to the greater Hartford area. They maintain a total of 38 active combined sewer overflow locations within their system that discharge in the Park River and the Connecticut River.
MDC has been working with the EPA and the Connecticut Department of Energy and Environmental Protection since the 1990’s to reduce overflows. From 2006 to 2022, they achieved a 50% reduction in yearly overflows, 488 million gallons in total.
In 2006, MDC entered into a consent order to implement actions that would eliminate all combined sewer overflows by 2029. However, in 2018 they released a Long-Term Control Plan update in which they requested an extension of nearly 30 years, to 2058 to finish the project.
Rather than granting a 30 year extension, CT DEEP approved a short term project list with a new consent order in 2022. Instead of the original goal of eliminating all combined sewer overflows by 2029, this new project list will achieve a reduction of 97 million gallons by 2029.
Projects that the MDC are required to complete include:
- Reducing CSOs in the North Branch Park River by 50% by 2027
- Completing the South Hartford Conveyance and Storage Tunnel by 2029 which will control South Branch Park River CSO’s and eliminate CSO’s going into Wethersfield Cove
- Eliminating 13 CSO/SSO regulators
2022 CT DEEP Consent Order with MDC
2018 Long Term Control Plan
The Clean Water Project
CT DEEP CSO Bypass map
The Springfield Water and Sewer Commission manages wastewater not only for the City of Springfield, but also for Agawam, East Longmeadow, Longmeadow, Ludlow, West Springfield and Wilbraham. For these seven towns, wastewater is conveyed to the Springfield Regional Wastewater Treatment Facility on Bondi’s Island in Agawam, where it is treated. Springfield has nearly 150 miles of combined sewer and stormwater pipes. During heavy precipitation events, the combination of stormwater and sewage is too great for the treatment facility to manage, and sewage is discharged, untreated into the Connecticut and Chicopee Rivers.
Since the late 1990s, the Commission has been working, under a series of Administrative Order from the EPA, to reduce CSOs. This effort has resulted in a 30% reduction in CSO volume since 1994 and in 2014, the Commission finalized a plan that outlines goals for further reducing CSO discharges. This plan, called the Integrated Wastewater Plan (IWP), outlines CSO reduction goals and steps, as well as steps to maintain and modernize existing wastewater infrastructure, such as the wastewater treatment facility. A primary goal of the IWP is to reduce CSO volume by 87% by 2031 using a 6-phase approach and prioritizing highest-volume, most cost-effective CSO projects.
Today the Commission manages 23 CSOs and is in Phase 2 of the IWP. A major project of Phase Two is the York Street Pump Station and Connecticut River Crossing Project. The project includes the construction of a new pump station as well as three new river-crossing pipes which will convey wastewater to Bondi’s Island for treatment. All told, this project will increase pumping capacity to reduce CSOs by 100 million gallons in a typical year and is slated to be completed in the summer of 2023.
From July – December of 2021 212 million gallons of untreated sewage were released into the Connecticut and Chicopee Rivers from the Springfield facilities. The completion of the York Street Project will mean a 51% reduction in CSO volume and is a major step in protecting the Connecticut River.
SWSC CSO and Stormwater Website
2014 Integrated Wastewater Plan
The City of Holyoke manages 12 active CSO outfalls from July – December of 2022 these outfalls discharged a total of 124 million gallons. The City has many miles of combined sewer lines, with 61% of the collection system combining stormwater and sanitary sewer lines.
In 2000, the City of Holyoke completed a Long Term Control Plan (LTCP), which has been superseded by the more up to date LTCP, finalized in 2019. Since 2000, the City has worked to separate sewer lines from stormwater conveyance, reduced inflow to the sewer system, made modifications to a number of CSO outfalls and constructed a treatment facility to address some CSO flows. All told, these projects have reduced annual CSOs by 316 million gallons, or roughly 66% since 2000.
Though there has been considerable progress made to reduce CSOs in Holyoke, there remains a significant amount of work over the coming years to work towards reduction and elimination of CSOs. In 2023 Holyoke and the Environmental Protection Agency entered into a consent decree which requires the City of Holyoke to implement the projects in the 2019 LTCP according to a schedule that concludes in 2037. The consent decree also includes requirements for the City to monitor stormwater and continue CSO monitoring.
The 2019 LTCP, which was updated in 2022, prioritizes abatement of three CSO outfalls. These outfalls were selected because they represent the lowest cost per gallon of CSO removed and would eliminate 3 out of of 4 highest volume CSOs with an overall anticipated 85% reduction in annual CSO volume.
2023 Consent Decree
2019 LTCP Summary
Public Notification Website
Similarly to Springfield, the City of Chicopee follows an integrated plan, called the Integrated Management Plan (IMP), which seeks to balance CSO abatement with upgrading critical wastewater infrastructure. The City manages roughly 200 miles of stormwater and sewerpipes, 70% of which were originally combined and has 15 CSO outfalls. From July – December 2022, the City discharged 64 million gallons and averages around 100 million gallons annually.
In 2006, EPA issued a Consent Decree to the City of Chicopee which mandated a schedule for implementing the LTCP at the time. Since 2006, CSO volume has been reduced from over 480 million gallons per year, representing a 75% decrease in CSO volume.
Looking ahead, the City of Chicopee is working to reduce annual CSO volumes by 85% by 2025 and by 99% when the IMP schedule is completed in 2050. Included in the IMP are both capital projects to address aging infrastructure and sewer backups, as well as CSO reduction projects. These projects are prioritized according to their level of “failure risk,” which helps to identify projects that will have the greatest benefit for human health and the environment while meeting regulatory requirements set out by the EPA.
2018 Integrated Management Plan
Public Notification Website
Montague is the smallest of the CSO communities, both in population and also in CSO discharge; in 2022, Montague’s two CSO outfalls released about 0.5 million gallons of sewage. In 2020, the town was issued an Administrative Order from the EPA to minimize its CSOs and meet additional limitations on discharges and to reduce harmful levels of bacteria in the Connecticut River. The Town of Montague created a new LTCP through a 2021 progress update, which is set to be finalized in the summer of 2023.
Since 2005, four of the six LTCP recommendations have been implemented and at this point, over 90% of the Town’s sewer system has been separated. Between 2005 and 2010 (when construction was completed on several projects), the Town of Montague reduced the number of discharged from 62 events per year to 14 overflow events per year. This constituted a reduction from 7 million gallons discharged per year, to 0.48 million gallons in 2011 and now averages roughly half of a million gallons of discharge per year.
Looking ahead, the 2021 LTCP update includes recommendations for completion by 2026 to reduce CSO discharged by 96%. These recommendations include GIS work to locate stormwater assets, hydraulic modeling to determine flow restrictions of the system and evaluate alternatives and field investigations to address identify sources inflow and infiltration into the system, which contribute to overflows.
Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) Update
Montague CSO Notification Page