Montgomery County, MD Environmental Rules: Stormwater Management (2026)
Key Facts
- Trigger
- 5,000 sq ft disturbance
- Standard
- ESD to maximum extent practicable
- Authority
- MoCo DEP + MDE MS4 permit
- Rebate
- RainScapes up to $2,500
- Bay TMDL
- N, P, sediment reduction required
Summary
Projects disturbing 5,000+ sq ft require a stormwater plan from MoCo DEP under Code Chapter 19. ESD techniques mandatory. Chesapeake Bay TMDL compliance required.
Polluted runoff (commonly called stormwater runoff) carries pollution and trash as it flows into our streams, lakes, ponds and rivers, making them unhealthy. Stormwater Management is the process where we slow, store, or allow stormwater to soak into the ground to help reduce the amount of pollution entering our waterways. Montgomery County uses above and below ground structures (we call them stormwater management facilities) to remove pollutants from the stormwater before the water gets to streams. The Stormwater Maintenance and Inspection Program is responsible for inspecting and ensuring the maintenance of all public and private stormwater management facilities within Montgomery County (excluding the municipalities of the City of Rockville, Gaithersburg, and Takoma Park). This includes ponds, levees, bioretention, underground facilities and Environmental Site Design (ESD) practices throughout the county. The program manages the structural and nonstructural maintenance of these facilities/practices on county owned property or that have been transferred to county maintenance using inspection and maintenance contractors. This also includes the Dam Safety Program. The program is paid for by the Water Quality Protection Charge (WQPC). The WQPC is a part of Montgomery County property tax bills and it raises funds to improve the water quality of our streams and reduce the impacts of stormwater runoff.
Full Breakdown
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.
Violations & Fines
Failure to obtain stormwater management approval before grading or construction results in stop-work orders and fines up to $10,000 per day under MDE enforcement. DEP may require retroactive stormwater management installation. Sediment discharge to waterways triggers additional MDE penalties.
Frequently Asked Questions
When is a stormwater management plan required in Montgomery County?
Can I get a rebate for managing stormwater on my property?
Sources & Official References
Other rules in Montgomery County
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