Maryland Highway Authority’s Stormwater Management Permit Must Set Precedent for Pollution Reduction

Advocates are calling on Maryland to take stronger action to reduce polluted runoff from state highways as the public comment period opens for a major stormwater management permit. Stormwater runoff is the fastest growing source of pollution in the Chesapeake Bay watershed.

Later this summer, the Maryland Department of the Environment (MDE) will issue a new Municipal Separate Storm Sewer System (MS4) permit to the Maryland Department of Transportation (MDOT)’s State Highway Administration (SHA). This permit will work to mitigate the harmful effects of oil, gas, and other pollutants that rainfall washes off highways into local waterways and the Chesapeake Bay.

The permit, which is designed to control pollution on the state's extensive highway system, will be crucial for preserving water quality. MDOT SHA manages nearly 15,000 lane miles and roughly 2,600 bridges. Maryland’s section of the Capital Beltway (I-495) and Baltimore Beltway (I-695) alone see volumes of over 220,000 vehicles per day, according to MDOT data

Given the immense surface area covered by this permit, it will mark a pivotal opportunity to effectively implement Maryland’s municipal stormwater program.

“As development in the Bay watershed grows and rainfall frequency and intensity increases from climate change, robust stormwater management will be more essential than ever,” said Allison Colden, the Chesapeake Bay Foundation’s Maryland Executive Director. “This permit has the potential to greatly enhance stormwater management, but it must include comprehensive and forward-thinking measures.”

In many cases, Maryland’s MS4 permits have fallen short for water quality improvements by relying on outdated rainfall data and prioritizing “check-the-box” practices that do little for habitat preservation and fail to sufficiently reduce pollution. SHA heavily depends on stream restoration to control pollution under its current permit, even though the practice is under fire for its questionable effectiveness. In 2023, the agency reported over 4,700 acres were treated via stream restoration, the most utilized mitigation practice by far. The second highest was outfall stabilization, or repairing erosion below storm drain pipes, at 700 acres treated.

“Some of the stormwater mitigation projects that have been proposed and are taking place in my community do more harm than good,” said Sharon Boies with Columbia-based grassroots organization, Protect Our Streams. “Stream restoration projects that receive MS4 credits too often allow environmental degradation like deforestation and, in the case of mitigation credits, allow the development of sensitive areas in additional locations as well. These shortcomings must be fixed by MDE statewide.”

Stormwater runoff is the fastest growing source of pollution in the Bay watershed, leading to erosion, habitat destruction, elevated levels of nutrient and chemical contaminants, and increased sedimentation.

The Chesapeake Bay Foundation and other environmental advocates are calling on MDE to incorporate the following critical enhancements into MDOT SHA’s new permit:

  • Ensure the permit accounts for increased storm intensity and other impacts of climate change;
  • Require a range of effective practices to mitigate stormwater pollution, such as riparian plantings, “green infrastructure” infiltration structures, and removal of unused impervious surfaces, to reduce reliance on in-stream projects;
  • Expand monitoring requirements to include temperature changes and impacts to wildlife and their habitats from polluted runoff; and
  • Track and address pollutants like polychlorinated biphenyls (PCBs) and ‘forever chemicals’ such as per- and polyfluoroalkyl substances (PFAS).

These measures are vital for protecting our waterways and communities from the damaging effects of stormwater runoff. Maryland residents can learn more about the Highway Authority’s MS4 permit and get involved here. MDE’s public comment period ends July 18.


Valerie Keefer

Maryland Communications & Media Relations Manager, CBF

[email protected]

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