Stormwater Regulations

As average rainfall rates increase and larger storms become more frequent, we can expect stormwater flooding to become an even greater challenge. The Clean Water Act regulates Municipal Separate Storm Sewer Systems (MS4s). The regulations are designed to address point source pollution from stormwater systems, yet the permit requirements can reduce flooding in addition to pollution by requiring greater infiltration of stormwater on project sites.

As of July 1, 2021, all MAPC communities needed to adopt local stormwater ordinances or bylaws for their areas subject to MS4 regulation. Post-construction runoff control will be required for projects of one acre in size or larger. Infiltrating a volume of runoff equivalent to one inch x the impervious surface area for new construction and .8 of an inch x the impervious surface area for reconstruction projects will meet the EPA requirement for removal of suspended solids and phosphorous. Some communities are achieving greater resilience by requiring additional infiltration and/or by lowering the threshold for application of the requirements.

State regulation of stormwater is addressed through the Wetlands Protection Act. Current wetlands regulations rely on rainfall data from 1961 to size stormwater infrastructure. MS4 requirements do not address rainfall rates. Many communities already use updated rainfall rates in their local wetlands regulations (see Wetlands Regulations for more information). Some have also updated rainfall rates in their stormwater regulations.

This page provides short summaries of key features of regulations based on desktop review. Links to the regulations are provided below. Conduct careful review when considering adopting new language. The resources included do not constitute legal advice. Municipalities should consult legal counsel when adopting new bylaws, ordinances, and policies.

Did we miss something? Do you have regulations or policies that should be added to this website? Do you need assistance? For additions, corrections, or questions please contact [email protected].

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Strategies to Strengthen Stormwater Regulations

Increase Infiltration Requirements Apply Stormwater Regulations to Less than One Acre Apply Updated Rainfall Requirements

Increase Infiltration Requirements

Dedham (246) requires that all projects infiltrate 2 inches x the impervious surface area.
The Boston Water and Sewer Commission requires projects greater than 100,000 square feet to infiltrate 1.25 inches x the impervious surface.
Cambridge (3.1) requires that projects infiltrate the difference between the post-project discharge for the 25-year 24-hour rainfall event and the 2-year 24-hour rainfall event pre-project discharge.

Apply Stormwater Regulations to Less than One Acre

The Dedham (246) bylaw applies to disturbances larger than 500 square feet. The bylaw also requires green infrastructure unless impracticable and includes tree planting as a stormwater management practice.
The Needham (7) bylaw applies to all new construction and any additions greater than 25% of the existing building footprint.
The Arlington (15) bylaw applies to increases in impervious surfaces that exceed 350 square feet.
The Winchester bylaw applies to activities that require a building permit and increase impervious surfaces by 500 square feet.
The Natick bylaw applies to disturbances of 3,000 square feet.
The Acton (X) bylaw applies to creation or disturbance of impervious surfaces greater than 5,000 sq/ft.
Marlborough (271) and Westwood (III) apply their stormwater regulations to disturbances of 5,000 sq/ft.
Wayland (193) applies their stormwater bylaw to disturbances of 5,000 sq/ft or 10% of lot area, whichever is less.
Burlington (6.0) applies their stormwater bylaw to disturbances of 10,000 sq/ft or greater.
Holliston requires a permit for disturbance of 10,000 sq/ft or 25% of the lot, whichever is less; paving of 500 sq/ft of commercial and industrial driveways, parking lots and other impervious non-roadway surfaces.
Ashland requires a permit for projects subject to Site Plan Review, disturbances of 10,000 sq/ft or more or increase impervious surface of 50% of a lot, and redevelopment of commercial, industrial, institutional, or multifamily residential parcels.

Apply Updated Rainfall Requirements