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

Section 33-4-102 sets the purpose of Article 33, Title 4: managing stormwater through environmental site design (ESD) "to the maximum extent practicable," using structural best management practices only when ESD cannot do the job, in order to reduce local flooding, stream channel erosion, and property damage. Section 33-4-104(a) makes the rule concrete: a person may not develop or redevelop a site without stormwater management measures that are consistent with the county's Design Manual and built under a plan the Department of Environmental Protection and Sustainability has approved.

Small projects get relief: developments that disturb 5,000 square feet or less of land, agricultural land management, and minor additions to existing single-family homes are exempt under Section 33-4-104(b), but the Director must certify any claimed exemption in writing. Everything else goes through three plan stages under Section 33-4-107, concept, development, and final, each adding detail on drainage areas, impervious area, and required storage volumes for recharge, water quality, channel protection, and overbank flood control. A stormwater management permit under Section 33-4-108 cannot issue until security is posted, an environmental agreement is executed, and the Soil Conservation District has approved the erosion and sediment control plan; permits expire two years after issuance, with one-year extensions available on written request.

Redevelopment sites carry their own math: Section 33-4-105 requires cutting existing impervious area within the limit of disturbance by at least 50%, or treating an equivalent share with ESD, unless the applicant pays into the county's Stormwater Management Fund.