Prioritization of Bacterial Indicator TMDL Compliance Activities in the Middle Santa Ana River Watershed in Southern California

Several waterbodies in the Middle Santa Ana River (MSAR) watershed are on the 303(d) list of impaired waters due to high concentration of bacterial indicators. The MSAR Bacterial Indicator Total Maximum Daily Load (TMDL), adopted by the Santa Ana Regional Water Quality Control Board, became effective May 16, 2007 when it was approved by the Environmental Protection Agency Region 9. The TMDL required preparation of an Urban Source Evaluation Plan (USEP) to identify specific activities, operations, and processes in urban areas that contribute bacterial indicators to impaired MSAR waterbodies. The approved USEP included investigation of bacterial indicators fecal coliform and E. coli and the use of bacteria source tracking (BST) methods for human, dog and bovine bacteria. Fecal indicator bacteria (FIB) concentrations frequently exceeded water quality objectives at the sampling locations. Bacterial indicator concentrations differed substantially between sites. FIB concentrations were higher during wet-weather than dry weather, as well as during the summer as compared with the winter seasons. BST analysis detected bacterial contamination originating from human sources at some sites. The detection frequency of human Bacteroides spp./Bacteroidales markers indicated that some tributaries to impaired waterbodies could pose a greater risk of exposure to harmful bacteria to potential downstream recreational uses than others. The study found that fecal coliform and E. coli concentrations were approximately 50 percent greater in samples where a human source was detected. The watershed stakeholders, including the MS4 stormwater permittees and Santa Ana Regional Water Quality Control Board, are using the 2007–2008 data results to prioritize the next steps for mitigating controllable urban sources of bacterial indicators.