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Numeric Action Levels: The New Driver for Stormwater Programs in Southern California

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During the renewal of the fourth term municipal stormwater permit for southern Orange County, the San Diego Regional Water Quality Control Board (Regional Board) incorporated, for the first time, dry weather and stormwater numeric action levels in the permit. As stated within the permit findings, the dry weather numeric action levels (NALs) are to be used as a part of the Illicit Discharge Detection and Elimination (IDDE) program element to detect and eliminate non-storm water and illicit discharges to the municipal storm drain system. Since the Orange County Permittees already had an IDDE program with action levels that had been developed and in full effect for several years, the incorporation of the new NALs required the Permittees to effectively overhaul their IDDE program and develop new investigative guidance in order to comply with the NALs and associated source identification requirements set forth within the Permit. For the past year the Permittees have used the guidance to investigate NAL exceedances, identify the sources, and prioritize the investigations.

Document Type: Research Article


Publication date: January 1, 2012

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