Montgomery County, MD Environmental Rules: Stormwater Management (2026)

Montgomery County regulates stormwater under County Code Chapter 19, Article V and Maryland Environment Article Title 4, Subtitle 2 (Stormwater Management Act of 2007). The county is subject to a Phase I Municipal Separate Storm Sewer System (MS4) permit issued by the Maryland Department of the Environment (MDE). Under the Chesapeake Bay Total Maximum Daily Load (TMDL), Montgomery County must reduce nitrogen, phosphorus, and sediment loads in stormwater runoff. Any development project disturbing 5,000 square feet or more of land requires a stormwater management concept plan approved by the Department of Environmental Protection (DEP) before a building or grading permit is issued. Environmental Site Design (ESD) techniques must be used to the maximum extent practicable, including rain gardens, bioretention, permeable pavement, green roofs, cisterns, and conservation landscaping. The county offers a stormwater management fee credit (RainScapes rebate program) of up to $2,500 for residential property owners who install qualifying stormwater management practices. WSSC Water manages the public water and sewer infrastructure but stormwater is managed separately by DEP. Residential properties pay an annual Water Quality Protection Charge (WQPC) based on impervious area, which funds stormwater infrastructure maintenance. Redevelopment projects must meet current stormwater standards even if the original development predates modern requirements.