Using a Risk Based Approach to address Bacteria Challenge and Attain TMDL Compliance
Managing water quality in California has long been challenging due to complex water quality problems, varied sources of pollutants and conditions, and pressures from regulatory agencies and environmental groups. Regulatory drivers, such as total maximum daily loads (TMDLs), focus on specific pollutants and include defined schedules for compliance, often developed prior to identifying necessary implementation actions. In San Diego, the Revised TMDL for Indicator Bacteria – Project I (bacteria TMDL) has been challenging to implement since its inception in 2010. Responsible parties have been charged with reducing fecal indicator bacteria (FIB) in the urban environment to protect recreational beneficial uses in local creeks and beaches. Sources appear to be ubiquitous and TMDL deadlines are looming. The interim date for dry weather compliance was April 4, 2020 and the final compliance date is April 4, 2021. While improvements have been realized, they often are not enough to attain compliance; therefore, responsible parties are moving to risk-based approaches to address sources of bacteria more effectively.
Since adoption of the TMDL, responsible parties have been implementing broad programs to address FIB. During this time, responsible parties have seen some improvements in water quality during, particularly at beaches in the region. In fact, data has been collected at several beaches to support delisting. In these areas, compliance with dry weather TMDL targets should be attained. However, in other areas, reductions in FIB have been more allusive and source investigations less fruitful. In these areas, compliance with dry weather targets is less certain.
Over the course of implementation, much has been learned about the fate and transport of FIB in the environment, sources, and solutions. In addition, several key studies have been performed in the region to support implementation and refine the science. Knowing that a more focused approach is needed to attain compliance, and supported by strong scientific evidence, some responsible parties are moving towards risk-based approaches focused on potential human sources of bacteria. Although discussions are ongoing to determine the exact compliance mechanism, many responsible parties are developing approaches to address potential sources of human waste in their watersheds, understanding that these sources have the greatest potential to impact human health.
While sources of human waste are numerous, the focus narrows the universe of potential sources and allows responsible parties to prioritize resources where they will have the greatest impacts. With potential sources ranging from sanitary sewer overflows and wastewater collections systems to RVs dumping waste into the storm drains, responsible agencies are building new relationships and improving existing programs, all supported by more refined monitoring efforts, to target these challenges. Their efforts will be further supported by new studies in the San Diego River Watershed that will better characterize sources of human waste and potential to affect beneficial uses.
This technical presentation will focus on three key areas that can be applied to agencies across the state facing challenges addressing bacteria. First, the presentation will illustrate how detailed desk top analyses can be combined with existing water quality data to support source identification and prioritization. Second, the presentation will show how source investigations and elimination can be combined with enhanced monitoring programs to support compliance. Third, the presentation will address adaptive management, including how new data and information will be considered to refine and improve the program and how this approach may support attainment of wet weather bacteria TMDL compliance deadlines (i.e., 2028, 2031) and potentially shellfish harvesting beneficial uses in the future.