Gaithersburg, MD Environmental Rules: Stormwater Management (2026)

Article III of Chapter 8 requires stormwater management for every new or redeveloped site, using environmental site design (ESD) to the maximum extent practicable (MEP) to keep post-development runoff as close as possible to predevelopment conditions (§ 8-17). The city incorporates the Maryland Stormwater Design Manual, 2000 Edition with ESD, plus county and state storm-drain design standards, by reference (§ 8-18). No person may develop land for residential, commercial, industrial, or institutional use without approved stormwater management measures, whether or not the project reduces impervious area (§ 8-19).

Exemptions are narrow: agricultural land management, additions to an existing single-family detached home, and any development or redevelopment that disturbs 5,000 square feet or less, unless it is part of a phased or larger project (§ 8-20). Even exempt projects lose the exemption once cumulative disturbed area, added over five years by the same responsible party, tops 5,000 square feet. The city manager or designee may grant quantitative or qualitative waivers only where ESD has been implemented to the MEP, and redevelopment projects must cut impervious area within the limit of disturbance by at least 50 percent, or provide ESD water-quality treatment for at least 50 percent of existing impervious area (§§ 8-21, 8-22). Variances from the stormwater management criteria in § 8-24 require a written request showing unnecessary hardship (§ 8-23).

A site or building permit will not issue without approved final erosion-and-sediment-control and stormwater plans, required easements, and a recorded maintenance agreement (§ 8-26). Before that permit issues, the city also requires a performance bond no smaller than the estimated construction cost of the stormwater system (§ 8-27) and, where the work could endanger people or adjoining property, a $2,000,000 liability insurance certificate (§ 8-28). The developer must give the city 48 hours' notice before starting work, and a city-certified erosion-and-sediment-control inspector conducts regular inspections through completion (§ 8-29). Private facilities need a recorded maintenance agreement and are reinspected in year one and at least every three years after (§ 8-30).