An Important Stormwater Case (and It's Not the One You're Thinking of)

Cross-posted from Environmental Law Prof Blog. Last week, a federal district court in Virginia decided an urban stormwater case that may ultimately have far more significance than the Supreme Court's more widely-watched decision in Los Angeles County Flood Control District v. Natural Resources Defense Council. The case is Virginia Department of Transportation v. U.S. Environmental Protection Agency, and it involves a challenge to a proxy TMDL for Accotink Creek, a Potomac River tributary in northern Virginia. On its face, that statement may not sound particularly intriguing or important, but it is, and a little background is in order. Section 303 of the Clean Water Act requires states to identify waterways that do not meet water quality standards, and to develop "total maximum daily loads," or TMDLS, for those waterways. In essence, TMDLs are pollution budgets. They usually identify which pollutants are causing impairment, and they then specify how much of a "load" of each offending pollutant the waterway could handle without being impaired. What happens next is largely up to the states. While EPA must step in to prepare a TMDL if the state fails to do so, states have broad discretion to decide whether and how to translate the TMDL into controls on individual sources. The Accotink Creek TMDL used an innovative approach. A traditional TMDL would specify a daily load for each offending pollutant, and would express that load as a mass. For waterways impaired by urban stormwater runoff, however, that traditional approach doesn't work very well, largely because saying exactly how much mass of each pollutant a waterway can accommodate each day is often quite difficult. Watershed scientists often have a much better sense of how much stormwater runoff a waterway can accommodate without being impaired, or even how much impervious cover in a watershed will trigger impairment. Consequently, the Accotink TMDL and several recent TMDLs developed in other states have used proxy measures of pollutant loading. For Accotink Creek, the proxy was the volume of stormwater runoff, and several TMDLs in Vermont have used similar approaches. In Maine and Connecticut, the proxy of choice has been impervious cover.