Challenge: To find creative solutions, using currently available data, to effectively mitigate risks from per- and polyfluoroalkyl substances (PFAS) to existing water supply operations and future investments.
Solution: The California-American Water (Cal-Am) Duarte System relies exclusively on groundwater supplies from the Main San Gabriel Basin. PFAS have been detected in several of the system wells. Despite an evolving regulatory environment and ongoing scientific understanding, Cal-Am must continue to invest in timely renewal and expansion of groundwater supply infrastructure. INTERA developed an innovative, systematic approach to evaluating PFAS risks using currently available hydrogeologic, water quality, and environmental site data. PFAS risks were assessed using a multi-step framework from a source to capture existing and potential well locations. Risk was quantified for potential sources of surface contamination, potential for leaching into the groundwater, and potential for capture by production wells. We worked closely with the Main San Gabriel Watermaster to delimit recharge areas and capture zones for the wells using groundwater modeling and particle tracking. This was combined with screening-level vadose zone modeling of PFAS transport to groundwater and review of historical water quality and environmental site data to evaluate the relative risk of contamination in each location.
Results: The results of INTERA’s analysis were used to provide practical recommendations for de-risking planned capital investments in future water production facilities. Potential new well sites were prioritized by relative risk, and recommendations for further investigation of specific well sites were provided. In addition, recommendations were provided addressing further characterization and identification of suspected sources of contamination, treatment, changes to pumping operations, and targeted monitoring to mitigate the risk and ultimate costs of addressing PFAS contamination.
