Adapting the Upper LA River Bacteria Load Reduction Strategy

The original Load Reduction Strategy (LRS) approach was pursued by the Upper Los Angeles River (ULAR) Watershed Management Group (WMG) as an alternative compliance pathway to address dry weather Los Angeles River Bacteria Total Maximum Daily Load (TMDL) requirements. Based on outfall monitoring data collected at the time, priority outfalls (consistently high E. coli loading rates) and outlier outfalls (episodically high E. coli loading rates) to be addressed were identified. As the ULAR WMG has moved forward with implementation, LRS efforts have broadly been focused on the development of dry weather structural controls. Initial designs were successful but in some cases feasibility issues arose, which were not considered in the initial prioritization. In addition to the implementation challenges, it is widely known that structural stormwater control measures may not be the most long-term, cost-effective solutions in reducing pathogens. Recent studies demonstrate human source control is a more cost-effective approach. Therefore, the ULAR WMG is adapting their LRS to expand on previous efforts with on-the-ground understanding of potential bacteria sources and the relation to public health risk. To do so, a more comprehensive prioritization was conducted based on water quality data, evaluating potential bacteria/pathogen sources, and considering additional information such as hydraulic connectivity to receiving waters to effectively guide cost-effective implementation actions. Planned efforts will be adapted, incorporating a greater emphasis on targeted source control, leading to a more successful program that better focuses on reducing human health risks in recreational waterbodies. The LRS adaptation update is timely given recent advancements in the development of human markers and other diagnostic tools to conduct source identification monitoring, which has been initiated in high priority areas. The overall approach leverages recent developments of an innovative risk-based pathogen health risk prioritization approach for Orange County that provides a model for this effort, similar work that is being conducted in the San Diego region, and the need to move expeditiously to reduce public health risks and demonstrate compliance with the LRS requirements.