Experts, Officials Clash Over Maryland’s Latest Stormwater Permit

A long-awaited stormwater permit for the Maryland State Highway Administration has become the latest flashpoint in dueling narratives over climate accountability and environmental justice in the state. 

The Maryland Department of the Environment (MDE) issues new permits for stormwater discharges “into, through, or from the municipal separate storm sewer system,” or MS4, every five years as required by the Clean Water Act’s National Pollutant Discharge Elimination System framework. The last permit expired in October 2023, but remained operative under federal and state law until a new permit was finalized.

The most recent permit, released Aug. 22, includes new requirements to curb polluted runoff from the state’s expansive road network that ends up in local creeks and streams, and eventually in the Chesapeake Bay.

Environmental advocates, while acknowledging that some public suggestions made it into the final draft, insist it still doesn’t go far enough in addressing climate-driven runoff from the state’s highways, lacks enforceable standards and offers few protections for overburdened, flood-prone communities. 

Representatives for the MDE say they did not want to further delay permit issuance while updating stormwater regulations based on future climate conditions, which the advocates argue is critical for adaptive stormwater management.    

Experts say the MS4 permit is a key regulatory tool under the Clean Water Act that governs how municipalities and state agencies manage stormwater discharges from separate sewer systems. 

These systems collect stormwater runoff from streets and highways and carry it into local water bodies without treatment. The goal of MS4 permits is to require jurisdictions to implement pollution-reduction practices, monitor their effectiveness and meet specific water quality benchmarks. 

Maryland’s MS4 program includes more than a dozen jurisdictions. The permit covers nearly 15,000 lane miles and roughly 2,600 bridges that fall under the SHA’s purview. 

Runoff pollution, shorthand for rain sweeping oil, metals, and other contaminants off paved surfaces, is the fastest-growing threat to the Bay, while pollution from agriculture and wastewater has lately declined, according to NASA’s Earth Observatory. More intense storms, rapid urbanization and expanding paved surface area are driving a surge in toxic runoff.

Communities across Maryland are already grappling with the consequences. Research suggests that warmer and wetter conditions are subjecting Maryland to more extreme weather events, including storms and flooding. Maryland received 7.81 inches of rainfall in May 2025—the most received in May in the past 131 years—according to the National Oceanic and Atmospheric Administration. 

Historically underserved neighborhoods are typically bearing the brunt of these infrastructure challenges. Climate-vulnerable cities like Baltimore are particularly affected by extreme weather. A 2018 study linked frequent sewage leaks in Baltimore’s Gwynns Falls neighborhood to stronger storms and greater rainfall, which had exacerbated pollution from stormwater runoff over the years and put more pressure on sewage pipes.

“This absolutely is [a rollback]. We are supposed to be constantly getting stronger permits, and here we have a manifestly weaker permit.”

— Evan Isaacson, Chesapeake Legal Alliance

Representatives from the Chesapeake Bay Foundation, Chesapeake Legal Alliance and the Maryland League of Conservation Voters say the new stormwater permit fails to incorporate updated rainfall data and undervalues low-cost, high-impact practices like tree planting and green infrastructure.

“We’ve been really pushing them to get that [stormwater] guidance updated and have it reflect the most recent stormwater volume data,” said Matt Stegman, an attorney with the Chesapeake Bay Foundation, referring to the state’s manual that outlines how stormwater volumes should be calculated and managed for MS4 permits. MDE periodically updates this document, which sets the standard for designing and implementing stormwater management projects. 

“It’s our belief that they have all the information available to them. What we don’t want to happen is continuing to have stormwater projects in the queue that are not sufficient because they’re relying on outdated data.”

One of the central points of contention is the permit’s restoration target. The new MS4 framework lowers the goal for treating runoff pollution by requiring action on 15 percent of hard, impervious surfaces such as roads, parking lots and rooftops—down from 20 percent in the previous iteration. 

“This absolutely is [a rollback]. We are supposed to be constantly getting stronger permits, and here we have a manifestly weaker permit,” said Evan Isaacson, senior attorney for Chesapeake Legal Alliance. “So yes, it is fundamentally inconsistent with the spirit and letter of the Clean Water Act.

“What’s confusing to me is they could have avoided this opposition by issuing 20 percent without even increasing the cost. It could have been done,” he added.

In a written response, the MDE acknowledged that the stormwater design manual is due for an update but defended moving forward with the permit. “We did not want to delay permit issuance that advances water quality and climate resiliency goals now,” the agency said, calling the permit part of “a broader package of clean water and climate initiatives” the Moore administration is pursuing. 

The MDE added that the change to impervious surface treatment requirements reflected an expansion in permit coverage and funding realities. “The requirement reflects a 15 percent restoration target—up from 11 percent in the draft permit—which is nearly a 40 percent increase in new acres restored,” the agency said. “This permit builds on past progress, sets ambitious but achievable goals, and establishes annual benchmarks to ensure steady momentum.”

The agency called the permit “the largest-ever SHA investment in stormwater restoration,” committing $216 million to restoration and “leveraging both state and federal dollars for the first time.”

The SHA, in its emailed comments, echoed the MDE’s view, noting the new target still equates to 4,092 acres of restoration. “Considering the need to manage and maintain previously completed restoration projects and the costs associated with those efforts, a 15 percent requirement is still an aggressive goal,” the state agency said. The SHA plans to meet this target through a combination of Best Management Practices (BMPs), including forest planting, meadow establishment, swales and using “smart ponds” as retrofits.

The previous permit’s 20 percent restoration goal instructed SHA to transform 4,621 acres of paved area for climate resilience, which it restored by the end date of the previous permit term. The agency said that “to date it has revamped a total of 6,480 equivalent impervious acres.”

It is also required to evaluate and report on stormwater project opportunities in overburdened communities. The agency pledged to submit two planning reports to the MDE: one evaluating previously completed projects and another projecting future implementation. The MDE said this requirement was “a first for an MS4 permit in Maryland and sets a precedent for stronger environmental justice accountability.”

Still, some critics remain unconvinced of the open-ended approach. “Let’s be smarter and more targeted about it, and put them in the communities that need them the most. Baltimore is a climate-battled place,” said Isaacson. “Baltimore residents feel more vulnerable to climate change than almost anybody else.”

Advocates also pointed to missed opportunities for stronger monitoring of thermal pollution and emerging pollutants such as PFAS, also known as forever chemicals. “Those flood waters in urban areas carry tens of thousands of different chemicals, a toxic soup that’s just sloshing through people’s communities and finding their way into people’s homes, their yards, their carpets,” said Isaacson.

In response, the MDE said PFAS risks are being addressed through other regulatory mechanisms better suited to drinking water and biosolids. “Runoff from highways is a far less significant source of PFAS,” the agency said, adding that thermal impacts are being addressed through revisions to water quality standards and temperature-related Total Maximum Daily Loads (TMDLs).

The SHA also defended its approach, pointing to its continued funding of the Chesapeake Bay Trust’s Pooled Monitoring Program. “Funding provided by SHA during this permit term will further expand the capacity of the Program,” it said.

Comparative analysis with other jurisdictions further complicates the picture. Advocacy groups submitted examples of other stormwater permits to the MDE to make the case for stronger numerical thresholds and enforcement to be included in the permit. 

Permits issued in western Washington and San Diego, for example, contained clearer performance benchmarks, enforceable numeric targets and structured monitoring frameworks. Maryland’s new permit only includes general guidance with no dedicated section on climate adaptation or rainfall-adjusted design standards. Its permit relied on discretionary language, according to the advocates’ comparison, and could use a better feedback mechanism for evaluating performance or integrating updated climate data.

Accountability and transparency provisions were found to be weaker in Maryland’s permit, according to the analysis. San Diego mandated outfall discharge monitoring and formal performance tracking, and western Washington required annual documentation and dedicated stormwater monitoring, which were not included in Maryland’s version. 

Environmentalists say the incremental gains reflected in Maryland’s permit are no longer sufficient. “We don’t want to say it’s not an improvement over the permit that it’s replacing. Our concern is just that it’s an incremental step forward, and we’re in a situation where incremental steps aren’t what’s needed,” said Stegman.

Isaacson put it more bluntly: “It’s a missed opportunity,” he said.