New Perspectives on Pollutant Sources and Regulatory Responsibility in Urban Watersheds
Within US EPA Region 9, several TMDLs have been developed with the assignment of wasteload allocations (WLAs) to stormwater sources including runoff from commercial, institutional, residential, industrial, highways, and secondary roads. Since the development of these TMDLs, NPDES permits have incorporated these WLAs as WQBELs to require implementation of stormwater controls to reduce pollutant loads from these sources. EPA recently completed an evaluation of the relative importance of stormwater loadings from commercial, industrial, and institutional land uses in southern California watersheds to assist in assessing the effectiveness of MS4 permits in regulating these sources.
The assignment of TMDL WLAs to MS4 permits is typically coarse in terms of the analysis of the relative impact of different sources or land uses within their designated areas. For example, MS4 permits include several land use types, but the pollutant loads from these separate land uses can be unclear. Also, the assignment of WLAs to other NPDES permits can often be limited and complicated as they relate to the MS4 Permit. For instance, only industrial areas registered in Industrial General Permit are required to meet WQBELs for that permit, leaving many unregistered industrial areas to fall under the responsibility of the MS4 permits. A further complication can be the WLAs themselves, as many are developed for an entire watershed covering all NPDES permits associated with urban runoff, leaving it up to the permittees to determine their portion of the WLA for implementation. Citizen groups recently petitioned EPA to require specific NPDES permit coverage for stormwater discharges from commercial, industrial, and institutional land based on the assertion that they are important pollutant sources and that existing regulatory mechanisms are insufficient to address them. Although EPA Region 9 denied the request to require additional NPDES permits for these land uses, further study was determined necessary to characterize the pollutant loadings from urban land uses and the costs for compliance with TMDL and NPDES requirements.
Two watersheds with multiple TMDLs addressing urban runoff were selected for analyses. Modeling was performed to assess pollutant (metals, bacteria, nutrients, PAHs) loads for the CII land uses and the BMPs necessary to attain WLAs and other relevant water quality objectives. We also began to consider how well existing NPDES permits address these sources. The study produced several conclusions that can nform future TMDLs and NPDES permits. Examples include analysis of the relationship between imperviousness, flow, sediment loads, and pollutant loads; pollutant loading from various land uses; BMP costs to treat pollutant loads; and considerations for future study. These results will inform future evaluations of how land uses within MS4s should be addressed in various permitting contexts, and how modeling can complement monitoring data to evaluate pollutant sources.
We intend to engage the audience in a discussion of how existing MS4 permits address land uses that are difficult to regulate and whether issuance of land-use targeted permits should be considered. As Chief of EPA Region 9’s NPDES Permits Section, David Smith will lead a discussion regarding how stormwater sources should be evaluated and regulated, and how we can learn from recent experiences in planning BMPs at finer geographical scales. He will share EPA’s latest perspectives on how difficult-to-control urban sources might best be addressed. Steve Carter will be able to discuss how model-based source analysis can assist in targeting the most important sources within stormwater control plans. The discussion will highlight new considerations in terms of how pollutant sources can be directly and indirectly addressed through regulatory mechanisms, providing additional assurance that those sources can be effectively managed to “make a difference” in improving water qualit