BWSC owns and operates a system for the collection and transport of stormwater in the City of Boston. The stormwater system collects stormwater runoff (rain and snowmelt) and discharges it into receiving waters around the city.
Approximately 80% of Boston is served by separate storm drains. The remainder of Boston is served by combined sewers, sanitary sewers only or is open space with no sewers or storm drains.
Discharges to BWSC’s separate storm drainage system are regulated under U.S Environmental Protection Agency’s (EPA) National Pollutant Discharge Elimination System (NPDES) Stormwater Permit Regulations. BWSC’s NPDES Stormwater Permit MAS010001 became effective on October 29, 1999.
Stormwater infrastructure is used throughout the city to capture runoff from rain or snow events via the 35,934 catch basins in city streets and sidewalks. Stormwater runoff is transported through almost 600 miles of the drain pipe and carried to one of the 207 stormwater outfalls where it discharges into one of several Boston water bodies.
The storm drain pipe infrastructure in Boston is made from polyvinyl chloride (PVC), reinforced concrete pipe (RCP), ductile iron, high density polyethylene, or corrugated plastic pipe. There are also still brick and clay storm drains within the city, though they are no longer constructed today. This infrastructure services most of the city's stormwater drainage needs. In recent years, new types of infrastructure have been used to manage stormwater; often referred to as green infrastructure.
BWSC controls most of the storm drains in Boston; however, some storm drains and outfalls are privately owned or are owned by agencies such as the Massachusetts Department of Transportation, the Massachusetts Turnpike Authority, Massport and the Department of Conservation and Recreation.
Under its NPDES Stormwater Permit, BWSC is required to develop and implement stormwater pollution prevention and management programs that are designed to reduce the discharge of pollutants to the municipal storm drainage system to the maximum extent practicable.
In addition, BWSC is required to report annually to the EPA and the Massachusetts Department of Environmental Protection (MassDEP) regarding the status of its pollution prevention and stormwater management programs. The annual reports provide summaries of stormwater management activities undertaken by BWSC including, descriptions of the outfall screening, monitoring, and illegal connection remediation programs. Also included are BWSC’s annual expenditures for stormwater programs and assessments of structural controls. See the Stormwater Reports link below for the annual reports.
Illicit Sewer Connections
The primary purpose of BWSC's Citywide Illicit Discharge Detection and Elimination Program is to identify building sewer connections discharging to storm drains. Such connections referred to as “illicit discharges” by BWSC, allow untreated sewage to discharge to storm drains, and from there to local waterways and wetlands.
The program includes field inspections and sampling of storm drain outfalls as a means of identifying sub-catchment areas suspected of having illicit discharges. In sub-catchment areas identified as contaminated, storm drain manholes are inspected and sewer connections from buildings are dye tested to identify illicit discharges. Storm drains and sewers are televised as needed to identify possible illicit discharges and defects that allow intermixing of storm drainage and sewage.
If a dye test of a building is necessary, owners and occupants of buildings are notified by mail. If an illicit discharge from a building is identified, BWSC will make arrangements to redirect the sewer connection to the sanitary sewer. In most cases, the correction can be made in the street. After the correction is made BWSC will need to perform another dye test of the building to confirm that it is properly connected to the sewer system.