What’s an MS4 Permit?

The Municipal Separate Storm Sewer System (MS4) Permit program is established under the Clean Water Act and is designed to prevent pollution from entering our water. Under the current Chesapeake Bay Agreement, MS4 permits in Maryland are intended to support our state goals to stick to the pollution diet, or Total Maximum Daily Loads, necessary for the health of the Chesapeake Bay. The State Highway Administration (SHA) is the one state-level entity regulated under an MS4 permit. Maryland Department of the Environment issues updated MS4 permits every 5 years. The first such permit was issued to SHA in 2005. You can find more information here.

While the intent of the MS4 permit program has been to reduce the pollutant loads from stormwater, we as a state have failed to achieve pollution reductions in stormwater. In fact, from 2009 to 2019 both nitrogen and sediment contamination into the Chesapeake Bay increased from developed land, according to an Environmental Integrity Project report.