Region 1: EPA New England
Reducing Combined Sewer Overflows to Charles River
During the first 12 years of the Clean Charles River Initiative, the top priority of the project has been to reduce bacteria levels in the river, based on Massachusetts bacterial water quality standard for swimming and boating.
Elevated bacteria levels are caused primarily by untreated sewage entering the river. There are a number of causes: old and broken sewage pipes, illicit connections to sewer storm water pipes, and "combined sewer overflows" (CSO).
CSOs are sewer systems that were designed to carry sewage and storm water in the same pipe to a sewage treatment plant. After heavy rainfall or snowmelt events, the wastewater volume is often more than the sewer system or treatment plant can handle. For this reason, combined sewer systems were designed to overflow after rain events and result in excess wastewater being discharged directly into rivers, lakes and coastal areas. The wastewater the CSOs carry not only contains storm water but also untreated human waste, industrial waste, toxic materials and floating debris.
For many years EPA targeted enforcement efforts on CSO discharges entering the Charles River that resulted from heavy rainfall or snowmelt events, causing surges of wastewater to enter sewer systems that are not equipped to handle the excess quantity, resulting in sewage being directly discharged into nearby waterways.
In March, 2006 EPA reached a landmark settlement with the Massachusetts Water Resources Authority (MWRA) requiring the MWRA to implement a long-term control plan to reduce CSOs throughout their sewer system, yielding sharp reductions in storm overflows to the Charles River.
The settlement with MWRA will bring CSO discharges to the Charles River down to approximately eight million gallons per year, from a 1988 level of 1.7 billion gallons. In addition to the major benefit to the Charles River, the drastic reduction of CSOs will help Boston to have among the cleanest river and beach environments of any major urban area in the nation.
Under the settlement, MWRA committed to take a number of actions at the Cottage Farm primary treatment facility. These include:
- Utilizing an abandoned 54-inch pipe beneath the Charles River to relieve pressure on the treatment facility during heavy storm events;
- Conveying additional flow to the Ward Street Headworks;
- Optimizing operations at the Cottage Farm facility (including the interconnection of sewer lines at the facility) to better balance flow; and
- Additional sewer separation in Brookline and Boston (including the Bullfinch Triangle area).
Triangle area). The MWRA will also perform an engineering evaluation of further system enhancements, including:
- Use of real-time controls at a number of overflow regulators;
- Modification of existing interconnections to better balance flow in a number of main sewer interceptors; and
- Evaluation of the construction of new interconnections between two main sewer interceptors in the vicinity of the Charles River.
These controls will result in a dramatic reduction of discharges from the Cottage Farm facility – including only two discharges per year, and no untreated discharges. Overall, the system improvements will eliminate more than two-thirds of the annual volume of wastewater overflows to the Charles that would have been allowed previously.