Identification and Control of Bacteria Sources: Lessons Learned from the Los Angeles River Watershed

Compliance with indicator bacteria (e.g., E. coli) standards poses an immense challenge to stormwater agencies in urbanized watersheds. Bacteria standards are designed to protect users of recreational waters (e.g., swimmers). As such, in order to resolve sources of bacteria, highlight potential human health risks, and prioritize actions to reduce bacteria discharges, it is recommended to monitor watersheds with a toolkit beyond indicator bacteria (USEPA, 2005). A premier application of an advanced bacteria toolkit was the Los Angeles River Bacteria Source Identification Study (BSI Study), which was funded by the City of Los Angeles Bureau of Sanitation and overseen by the Cleaner Rivers through Effective Stakeholder-led TMDLs (CREST) stakeholder group. There were many lessons learned during the BSI Study, which can be summarized by six primary “themes”:An indicator is not an indicatorIf human indicators are really high, then so is E. coli, but that's about itTrickles are importantCausing exceedances depends on the viewpointDefining “worst” or “most problematic” is not straightforwardMonitoring data is much more useful as a statistical modelThe BSI Study provided stakeholders with a wealth of scientific information that can be used to better understand bacteria and virus fate and transport in the LA River watershed. In fact, the BSI Study represents the state of the science with respect to assessing bacteria sources, and is perhaps the most advanced study of bacteria and viruses in urban runoff conducted to date. The extensive monitoring and data analyses conducted during the BSI Study could be used as a model for stakeholders motivated to identify the early action items for TMDL implementation that have the highest probability of improving water quality and reducing human health risks.