Stormwater Management

A catch basin is a curbside receptacle whose function is to convey water from streets and other impervious surfaces into the storm drainage system. The design of this drainage structure includes a sump and hood that captures and temporarily stores some pollutants such as oils and sediment. Maintenance to clean out the sump removes the stored pollutants and prevents them from washing further into the storm drain system and into receiving waters such as the Charles River and Alewife Brook.

Impervious surface means those disturbed or hard surfaced areas that either prevent or restrict the natural entry of water into the soil. Rooftops, buildings, streets, parking lots, sidewalks, asphalt, concrete, other paving, driveways, gravel, patios, artificial turf and storage areas are all examples of impervious surfaces. Impervious areas effect natural infiltration, creates more runoff, increases the rate of runoff and alters runoff patterns of stormwater that drains from an area.

Stormwater is water from rain and snowmelt. As rain and snow falls to earth in forested and undeveloped areas, it is either absorbed or it slowly runs off and dissipates. Learn more about how stormwater is part of the water cycle here: Surface Runoff and the Water Cycle | U.S. Geological Survey (usgs.gov).

In a dense urban environment like Cambridge, where rooftops and paved areas not only prevent the water from being absorbed, but also help it run off at a much faster rate, problems arise. Unmitigated, the stormwater could accumulate, causing nuisance flooding and possible threats to public health and safety. Flooding is only a part of the problem. As the rain falls onto our streets and runs off, it carries with it pollutants such as pet waste, gasoline, oil, and heavy metals. Pesticides, herbicides, and fertilizers are washed from lawns and other green spaces. Sediments are eroded by wind and water from construction sites and unvegetated landscape areas. With the passage of time, these pollutants will buildup in our local waterways causing environmental damage.

Paint thinner and paint products, used motor oil and antifreeze, pesticides and fertilizers, sediments containing heavy metals, cigarette butts, trash, human and animal feces, golf balls, dirty diapers, and dead animals are but a few of the many pollutants found in the system on a regular basis. We all have the ability to help reduce stormwater pollution by taking individual actions to pick up after our pets, dispose of trash and wastes properly, and use fertilizers and insecticides sparingly and wisely.

Most of the time they are two completely separate systems. The sewer system, also known as the sanitary sewer or wastewater sewage system, conveys household, commercial and industrial wastewater through a separate plumbing system into an underground sewer pipe system. Wastewater in the sanitary sewer system is from sources such as water and waste from sinks, toilets, washers, and car washes, to name but a few. Discharges to the sanitary sewer system is conveyed and treated at the Deer Island Wastewater Treatment Plant prior to being discharged into Boston Harbor. The storm drain system on the other hand, discharges primarily untreated stormwater runoff directly into the Charles River or Alewife Brook. In Cambridge we also have combined sewer systems that carry both wastewater and stormwater in a single pipe. During small rain events all flows are treated and discharged at Deer Island, but during significant rain events the increased stormwater can cause untreated combined sewer overflows to the Charles River and Alewife Brook.

A watershed is made up of the land area that drains to a specific body of water.  Cambridge lies within two watersheds, the Charles River and Mystic River watersheds.  Everyone lives in a watershed.  Check out the Cambridge Watershed map.

Learn more about water quality in the Mystic River on the Mystic River Watershed Association’s webpage here and the Mystic River Watershed Report Cards here.

Learn more about water quality in the Charles River on the Charles River Watershed’s Association’s webpage here and the Charles River Watershed Report Cards here.

In accordance with the City’s Municipal Separate Storm Sewer System (MS4) Permit, Cambridge is developing a Phosphorus Control Plan to address stormwater runoff to the Charles River. As part of the City’s stormwater program, Cambridge is working to reduce its current phosphorus loads to the Charles River through a combination of non-structural controls, like street cleaning, and structural controls, like tree box filters and rain gardens. Phase 1 of this plan must achieve the first 25% of the City’s phosphorus load reduction requirement by June 30, 2028.

A factsheet is also available, which summarizes the impact of excess phosphorus in water bodies and key elements of the City’s plan.

Link to Phosphorus Control Plan Factsheet
Link to Phosphorus Control Plan