Achieving Bacteria Compliance in the Upper Los Angeles River Watershed Through a Human Health Risk-Based Approach

Bacteria impairments remain one of the most challenging water quality issues to address in Southern California, resulting in beach closures and unsafe conditions for recreators. The Upper Los Angeles River Watershed is pursuing an innovative method to address the Los Angeles River Bacteria Total Maximum Daily Load (TMDL) requirements. When the Bacteria TMDL was developed in 2010, a pathway towards compliance was established based on outfall monitoring data collected at the time to identify priority outfalls (consistently high E. coli loading rates) and outlier outfalls (episodically high E. coli loading rates) and a Load Reduction Strategy (LRS) to implement control measures to address. However, following years of implementation challenges and evolving understanding of human health impacts and risks related to bacteria impairments, an adapted, data-driven approach is now being used to reprioritize effort to focus on more feasible and effective strategies. Specifically, efforts are refocused on the highest risk source of illness-causing pathogens (i.e., human waste) and the highest risk areas of the watershed, where it is more likely illness-causing pathogens are present. A renewed emphasis is placed on targeted source control in management strategies. Recent studies demonstrate that human waste source control is a more cost-effective long-term approach to reducing pathogens associated with bacteria. Human waste typically contains a higher concentration of pathogens, thereby increasing the risk of gastrointestinal illness through recreational exposure. In response, the adapted approach in the Upper Los Angeles River expands on previous efforts with on-the-ground understanding of potential bacteria sources and the relation to public health risk. Human waste source control is a more cost-effective long-term approach to reducing pathogens relative to typical structural BMPs. Further, advancements in human marker tools-such as HF183-can better identify conditions under which pathogens are contributing to downstream impaired receiving waters. The Upper Los Angeles River Watershed is implementing this innovative risk-based prioritization, using advancements in source investigation tools, robust data collection and processing, and a newly developed human waste source identification and tracking toolbox to conduct human waste source investigations to reduce public health risks and help restore the beneficial uses of the iconic LA River. Robust data collection and processing was conducted across agency departments to shine a new light on potential dry weather flows and pathogen sources in the watershed and prioritization results used to delineate areas of investigation (AOIs), focusing limited management resources in areas posing the greatest risk. Human waste source investigations are being conducted in the top priority AOIs to isolate the contributing sources for targeted abatement strategies. This presentation will discuss the data-driven prioritization approach and selection of areas of investigation, the strategic risk-based monitoring being implemented, and the results and lessons learned from the human waste source investigations performed as part of the special study. The methods developed and employed in this watershed promise to materially improve bacteria management success in Southern California and beyond, available online as a template and for communicating progress through the Upper Los Angeles River: Load Reduction Strategy Adaptation Story Map (https://storymaps.arcgis.com/stories/466afe14077a436aabd8f072ed20ee2e).