COMBINED SEWER OVERFLOWS
WHAT IS A COMBINED SEWER OVERFLOW (CSO)?
Combined Sewer Overflows (CSOs) are overflows of untreated sewage and stormwater into local waterbodies.
WHY DOES THIS HAPPEN?
Combined sewer systems collect rainwater runoff, domestic sewage, and industrial wastewater in a single pipe system. Typically, combined sewer systems transport all of their wastewater to a sewage treatment plant, such as Deer Island. However, during periods of heavy rainfall or snowmelt, the wastewater volume in a combined sewer system can exceed the capacity of the sewer system or treatment plant. For this reason, combined sewer systems are designed to overflow occasionally and discharge excess wastewater directly to nearby streams, rivers, or other water bodies.
CSOs AND THE MYSTIC RIVER WATERSHED
CSO's are a major pollution concern for the Mystic River Watershed. CSO's contain not only stormwater but also untreated human and industrial waste, toxic materials, and debris. Pollutants associated with such overflows pose a risk to public health, impact water uses (swimming/boating/fishing), and stress the aquatic environment.
Based upon water quality data collected on the Mystic and its tributaries since 2000, the Mystic River Watershed Association recommends that whenever it rains people should revise their water-based recreation plans such as boating, fishing, or swimming on the Mystic. In general “wet weather” conditions are a high level predictor for poor water quality in the Mystic River Watershed from various pollutant sources. These poor water quality conditions can occur whenever it rains regardless of a CSO event due to stormwater runoff and local plumbing problems (illicit connections). Bacterial contaminants typically last for 48 hours.
Where does this happen? Click here for a Massachusetts Water Resources Authority (MWRA) map of CSO outfalls and control projects. Currently, the City of Cambridge reports CSOs to Alewife Brook most frequently within the Mystic River Watershed.
WHAT IS BEING DONE?
Find out how the Massachusetts Water Resources Authority (MWRA) is addressing CSOs here. Look on your city's website to find out what is being done by your city. MyRWA's Policy Committee advocates for improvements to the sewer and stormwater system to minimize CSO occurances.
You can also review the April 15, 2010 Alewife Brook Combined Sewer Overflows Progress Update. This is a joint public notice produced by Massachusetts Water Resources Authority (MWRA) and the Cities of Cambridge and Somerville.
Get informed! Please email us at: email@example.com if you would like to be notified about future CSO alerts. Contact your local municipality by clicking the link here for any concerns you may have.
It should also be noted that the MA Department of Public Health has issued a fish consumption advisory for several rivers and ponds in the Mystic River Watershed against consuming fish caught in these waters. For more information, contact MDPH Bureau of Environmental Health at 617-624-5757.
CSO activation in Alewife Brook occurred on the following dates in 2013: See the CSO alerts on the City of Cambridge news website here.
USEFUL LINKS & PRESS
- Mass.gov web page
- Environmental Protection Agency's (EPA) CSO webpage
- Massachusetts Water Resources Authority (MWRA) web page on CSOs