The sewers in Pawtucket and Central Falls are combined sewers. This means they convey not only sanitary sewage from homes and businesses, but also stormwater that runs off streets and buildings. In times of heavy rain, the sewers can become overwhelmed by the stormwater causing the pipes to overflow into the Seekonk River. This combined sewer overflow (CSO) compromises the water quality in the rivers and upper Narragansett Bay. CSOs are illegal under the Federal Clean Water Act and NBC is under a federal mandate to minimize CSOs.
For years, sections of the waterways and the nearby beaches, had been closed to the public because of water quality. Fishing, particularly shellfishing, in the Bay had been limited for many years, especially in times following heavy rainfall.