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View of Alewife Brook

Stormwater Management

About Stormwater Management

Stormwater runoff is generated when precipitation from rain and snowmelt flows over land and does not soak into the ground. As runoff flows over impervious surfaces (paved streets, parking lots, and building rooftops), it accumulates debris, oil, pet waste, chemicals, sediment or other pollutants that could adversely affect the  quality of nearby waterways if untreated. 

Stormwater management is a combination of engineering, construction, site maintenance and public outreach efforts to address runoff quality and quantity.  Structural controls such as pipes, catch basins, and grit chambers are used to control both the quantity and rate of stormwater runoff and the quality of stormwater discharged to water bodies.  Non-structural controls such as water quality monitoring, vegetative swales, public education, and policies relative to pest management, fertilization and construction erosion control are also important. 

Illegal Dumping

Runoff enters the storm drainage systems through catch basins. Storm drains often lead directly to streams, rivers, lakes, or beaches. Cambridge storm drains discharge to the Charles River or to the Alewife Brook. Please don't dump! Residents are encouraged to report illegal dumping by calling the Department of Public Works at 617-349-4800, sending an email or reporting via Commonwealth Connect app or website. Dumping anything but unpolluted water into storm drains (catch basins) is illegal. Items that should be reported include motor oil, antifreeze, soapy water, pet waste, yard clippings, paint and construction debris.

Who is responsible for protecting waterways?

Protecting the waterways is a joint responsibility between residents, developers and contractors, businesses and industry. Click on each of the webpages below to find actions each audience can take to help keep stormwater clean.


Developers and Contractors



What is the City doing to protect waterways?

Stormwater Management Program (updated June 2023): 

The Cambridge Stormwater Management Program (SWMP) is a program of stormwater mitigation actions for the City of Cambridge based on the guidelines established under the Municipal Separate Storm Sewer System (MS4) stormwater management program by the U.S. Environmental Protection Agency’s (EPA) National Pollutant Discharge Elimination System (NPDES) Stormwater Phase II Rule. The Stormwater Management Plan will be updated in 2020 in accordance with the requirements of the 2016 MS4 Permit and Notice of Intent submitted to EPA on September 28, 2018.

The City annually reports activities completed under the Stormwater Management Program to EPA. Annual reports and associated documentation is available on the City’s website here.


What is a catch basin?

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.

What is an impervious surface?

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.

What is stormwater and why is it a problem?

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.

What kinds of pollutants are found in the storm drain system?

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.

Are sewers and storm drains the same thing?

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.

What watershed do I live in?

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.

What are the main components of the City's Stormwater Management Program?

The regulations specify that compliance with the MEP requirement can be attained by developing a SWMP that addresses the following six minimum control measures:


Control Measure


Public Education and Outreach Implement an education program that includes educational goals based on stormwater issues of significance within the City. Objective is to increase public knowledge and change behavior so that pollutants in stormwater are reduced.
Public Involvement and Participation Provide opportunities to engage the public to participate in the review and implementation of the SWMP.

Illicit Discharge Detection and Elimination (IDDE) Program (updated June 2023)

Catchment Areas and Outfalls Map

Implement an IDDE program to systematically find and eliminate sources of non-stormwater discharges to the municipal separate storm sewer system and implement procedures to prevent such discharges.
Construction Site Stormwater Runoff Control Implement a construction site program to minimize or eliminate erosion and maintain sediment on site
Stormwater Management in New Development and Redevelopment (Post Construction Stormwater Management) Implement a program to reduce the discharge of pollutants found in stormwater through the retention or treatment of stormwater on site after construction is completed.
Good House Keeping and Pollution Prevention for Permittee Owned Operations(Updated September 2023) Implement an operations and maintenance program for municipal-owned operations that has a goal of preventing or reducing pollutant runoff and protecting water quality.


    What is the City's IDDE Program?

    IDDE stands for Illicit Discharge Detection and Elimination. The goal of the City’s IDDE Program is to find non-stormwater discharges to the City’s drainage system through water quality sampling and investigations. When these illicit connections are found, the City works with property owners or completes infrastructure repairs to eliminate them. 

    Phosphorus Control Planning?

    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

    Page was posted on 3/18/2019 6:08 PM
    Page was last modified on 6/7/2024 11:49 AM
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