Climate Resilient Land Use: Stormwater Regulations

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Climate Resilient Land Use: Stormwater Regulations

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 Senior Environmental Planner Anne Herbst at aherbst@mapc.org.

Strategies to Strengthen Stormwater Regulations

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
Apply Updated Rainfall Requirements