Somerville, MA Environmental Rules: Stormwater Management (2026)

Somerville is regulated under the EPA MS4 General Permit for small municipal separate storm sewer systems. The City's Stormwater Ordinance and design standards, administered by DPW Engineering and the Conservation Commission, require that any project disturbing 1 acre or more obtain an EPA Construction General Permit (NPDES) and file a Stormwater Pollution Prevention Plan (SWPPP). Locally, smaller projects adding 500 square feet or more of new or replaced impervious area must submit a site-specific stormwater management plan demonstrating no net increase in peak runoff, typically using infiltration basins, rain gardens, or underground detention. Illicit discharges (paint, soap, concrete washout) to the storm drain are prohibited and carry fines up to $5,000 per day. The Mystic River watershed is particularly sensitive and triggers additional nutrient controls.