Municipal stormwater regulation in the United States has historically been built around a pragmatic directive from Section 402 of the Clean Water Act: Reduce the discharge of pollutants of concern to the maximum extent practicable (MEP). This is commonly understood to require use of the most effective best-management practices that are technically feasible and economically reasonable.

The MEP standard is intentionally flexible and allows communities to make progress while balancing environmental protection with practical realities such as cost, land constraints and local priorities.

Recently, another regulatory framework has increasingly been layered onto municipal stormwater permits: water-quality-based effluent limits derived from total maximum daily loads (TMDLs).

TMDLs determine how much pollution a waterbody can receive while still meeting water-quality standards. But TMDLs are not self-implementing. To make them enforceable, regulators often incorporate them into stormwater permits as water-quality-based effluent limits (WQBELs).

A Fundamental Tension

The MEP framework is adaptive and effort based. Compliance typically is evaluated by whether municipalities are implementing reasonable programs and control measures and improving stormwater management through time.

WQBELs, by contrast, were designed for point sources such as wastewater treatment plants, where discharges can be measured and tightly controlled. Compliance depends on meeting numeric limits and deadlines.

Urban stormwater systems rarely operate with that level of control. As a result, municipalities often struggle to meet WQBEL deadlines tied to TMDL allocations. When that happens, regulators typically issue compliance extensions or additional program requirements—creating a cycle of escalating costs without clear evidence that water-quality standards will ultimately be achieved.

Los Angeles offers a useful example of how communities view this challenge. Voters approved the Safe Clean Water Program, a parcel tax that funds regional projects to capture and infiltrate stormwater. The program reflects a clear community decision to invest in watershed improvement at a defined cost.

At the same time, regulators are proposing new requirements under the draft Commercial, Industrial and Institutional (CII) stormwater permit. The permit would bring roughly 600 existing commercial and industrial properties in two heavily urbanized watersheds under a new NPDES permit structure that effectively pushes responsibility for receiving-water impairments down to individual parcels. Even if these facilities fully comply, there’s little expectation that the affected waterways will achieve all designated beneficial uses.

Water Board staff estimates suggest that stormwater retrofits needed for compliance could cost hundreds of thousands of dollars per acre of impervious area, with multi-acre industrial sites potentially facing capital costs in the millions. For many facility operators, those costs may not be absorbable. Therefore, the likely result isn’t universal compliance but economic displacement with many businesses relocating to other regions or closing altogether.

This raises two fundamental questions we must be able to confidently answer “yes” to if we expect the public to support these programs. Are we directing environmental resources where they will produce the greatest benefit? And does this level of expenditure for the expected environmental benefit have the informed consent of the communities bearing the cost?

Path Forward

In heavily urbanized watersheds, opportunities for meaningful improvement often are constrained by decades of development and legacy pollution. Attempting to achieve marginal gains through expensive parcel-level retrofits may not always be the most effective strategy.

A more constructive path forward may be to expand the scale at which compliance is achieved.

Rather than requiring every property to install costly controls, regulators could allow permittees to participate in watershed-scale programs that fund projects delivering the largest water-quality improvements. Investments might support stream restoration, regional treatment facilities, sediment remediation, headwater protection or other projects that produce measurable pollutant reductions.

Such an approach wouldn’t abandon regulatory accountability. Pollutant reductions could still be quantified and tracked at the watershed level, preserving the outcome-oriented goals of WQBELs while restoring the flexibility that has long been central to the MEP framework.

Communities have already shown they are willing to invest in cleaner water. The challenge now is ensuring that regulatory systems give them the flexibility and transparency to ensure those investments deliver the greatest environmental benefit.