Recently, industrial, commercial and municipal NPDES discharge permits have been required for dischargers in selected areas that have not previous been required to obtain such permits, under existing applicability requirements. This requirement has been in conjunction with impaired waters Total Maximum Daily Load (TMDL) studies, in which stormwater sources are a significant contributor to impairments. The basis for this extension of NPDES permit requirements has been based on the “Residual Designation Authority” given to US EPA under the Clean Water Act. The most recent examples of the use of the residual designation authority have been in Maine, Massachusetts, and Vermont.

Under the Clean Water Act “Residual Designation Authority” EPA can require permits from additional dischargers where a TMDL supports such a determination and where discharges are contributing to water quality violations. EPA’s residual designation authority is provided by Section 402(p)(2)(E) and (6) of the Clean Water Act (CWA) and promulgated by 40 CFR 122.26(a)(9)(i)(C) and (D). In Vermont and Maine, local organizations filed formal legal petitions with appropriate regulatory agencies seeking this extension on a watershed-wide basis. EPA has indicated that it intends to move forward with broader roll out to address the numerous waterways polluted as a result of stormwater runoff.

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