Stormwater BMP Surveys

Searching out the best places to install structural stormwater BMPs.

The Problem

Snowmelt carries stormwater pollution into a catch basin.

Snowmelt carries stormwater pollution into a catch basin.

Whenever it rains, or when snow melts, the associated water washes across the landscape, accumulating pollutants and creating “stormwater.” Pollutant-infused stormwater is one of the biggest challenges facing watersheds and water quality, today.

Oil, grease, sediment, salt, bacteria, pesticides and animal waste may all contaminate stormwater, depending on the surfaces with which the water came into contact.

When not infiltrating the ground, stormwater washes across hardened (“impervious”) surfaces, eventually entering a catch basin attached to a network of piping, and is discharged to a water body.

With few exceptions, most Neponset Watershed stormwater enters the river untreated – a major contributor to Neponset River’s failure to meet fishable/swimmable water quality standards during wet weather.

Treating stormwater before it is discharged into the river and its tributaries is key to helping the Neponset and its tributaries meet water quality standards. The hard part is finding places where this treatment can occur. Over the past few years, the Watershed Association has been working with towns to find the best places to install structural stormwater Best Management Practices (“BMPs”). These BMPs help to treat stormwater and clean it before it discharges to the river.

What Are BMPs, and Why Do We Need Them?

Best Management Practices either can be structural or nonstructural, and as simple as cleaning up after your dog or as complicated as building a man-made wetland system. Each has its place and has some degree of effectiveness at helping to reduce stormwater pollution.

The Watershed Association largely has chosen to identify areas to implement structural BMPs because they typically can treat much larger portions of the watershed, and thus larger volumes of stormwater.

Since the Neponset River most often violates water quality standards with regard to bacteria, our projects focus on BMPs that best treat bacterial pollution. Fortunately, the practices that are best for bacteria are also some of the best overall BMPs and treat a wide variety of pollutants equally well.

BMPs that best treat bacteria do so largely through filtration and/or infiltration. Water enters the BMP and undergoes a pre-treatment step that manages sediment, to help to ensure that the rest of the BMP doesn’t get clogged over time. The water either then filters through a soil-based medium or is allowed to infiltrate the ground. Different types of plants can be added to BMPs to absorb excess nutrients, like phosphorus and nitrogen.

Although there are BMPs of varied styles and configurations, the basic premise behind treatment is relatively the same.

In terms of effectiveness, BMPs that infiltrate are preferred, since they not only clean the water, but allow it to recharge groundwater supplies, keeping river flows more consistent.

To infiltrate stormwater, porous soils are needed. Unfortunately,  locations containing adequate space to build a BMP don’t always contain such soils. In those cases, alternative structures that filter stormwater, rather than infiltrate it, can be used.

Stormwater BMP behind the new Walpole Public Library.

Stormwater BMP behind the new Walpole Public Library.

Examples of BMPs

  • Bioretention cells
  • Raingardens
  • Filter strips
  • Pocket wetlands
  • Infiltration basins
  • Treebox filters
  • Dry wells

Where We Are Looking

The focus of these partnerships between the Watershed Association and watershed towns has been two-part: 1) To identify areas in each town in which structural BMPs could be installed, and 2) To make recommendations of the types of BMPs that would be most effective at each location.

The Watershed Association has been working with a number of watershed towns to locate the best locations to install stormwater BMP retrofits. As of writing, we have completed work in Sharon, Stoughton, Walpole, Canton and Dedham. Work continues in the Town of Milton, to be completed this summer.

In each town, the Watershed Association has worked with the DPW, Engineering, and Conservation Commission staff to make recommendations for BMPs. We placed an emphasis on publicly-owned locations as potential BMP locations. We considered town-owned, Department of Transportation, Department of Conservation and Recreation, and Federal lands as top prospects. We then whittled-down our recommendations to the 10 best locations at which BMPs would not only be most effective but also that had the fewest barriers to implementation and could treat the largest amount of stormwater. Project partners completed further investigations in the field to yield the top three or four locations in each town, and a consulting engineering firm produced preliminary BMP designs.

Top Locations in Surveyed Towns



Top three locations are located along Billings St., at the end of Brook Rd., and along Hixson Farm Rd.:


Top three locations are the parking lot behind the Police and Fire Stations, at the Fisher Elementary School, and also at the Johnson Middle School:


Top three locations are at the Hanson Elementary School, the Gibson Elementary School, along Morton St., and also near Mark’s Field off of Blackstone St.:


Top four locations are at the Hansen School, Galvin Middle School, the parking lot at Ponkapoag Golf Course, and Canton High School:


Top three locations are at the intersection of Colburn St. and Whitehall St., along Avery St., and at the intersection of Sawmill Ln. and Emmett Ave.:

Learn More

Find out more about the BMP Surveys completed in Sharon, Stoughton, Walpole, Canton and Dedham. View the final reports, below.

Each report details survey locations and methodology. The reports also provide a more comprehensive explanation of the results in each town. For example, for the top three or four locations in each town, find information on the size of the proposed BMP as well as its potential pollutant removal efficiency. You also can find cost estimates both for implementation of the BMP practice as well as long-term maintenance costs.

Sharon, Stoughton and Walpole Final Report

Canton Final Report

Dedham Final Report

Next Steps

Now that we have located these great locations and recommended BMPs, it’s time to make things happen! The Watershed Association has been working with the towns that have initial surveys, to locate funding for BMP installation.

The Watershed Association also continues to pursue ways to partner with watershed towns that have not been surveyed.

If you would like to see your town surveyed for BMP sites, we encourage you to write or call the Town’s Engineering Department, Department of Public Works, and/or the Conservation Commission. Let them know about the BMP work of the Watershed Association and that you would like to see it duplicated in your town.

For more information about these surveys and their results, please contact Chris Hirsch, Environmental Scientist, or 781-575-0354 x302.

Special thanks to ESRI for donation of ArcGIS and ArcPad software that was used during this project.