Challenge: The Montebello Forebay is an area that has been used for decades for large-scale recharge of stormwater and treated wastewater to the Central Basin. Per- and polyfluoroalkyl substances (PFAS) have been detected in numerous wells in the Central Basin, some exceeding California’s strict Notification Levels (NLs) and Response Levels (RLs) for PFAS. To inform basin management, WRD needs to understand the distribution of PFAS in the subsurface.

Solution: INTERA dynamically profiled and sampled three groundwater production wells to evaluate the distribution of PFAS in the subsurface and the zonal contributions of PFAS compounds to the production wells. INTERA partnered with BESST, Inc. to utilize patented miniaturized downhole tooling to complete depth-dependent, dynamic flow and water quality profiling under normal operating conditions. PFAS sampling was conducted following EPA Method 537 Ver 1.1 protocol to minimize external contamination. The production well sampling data was compared to water quality data from multi-level monitoring wells to understand the regional and depth-specific distributions of PFAS.

Results: The analysis was used to provide recommendations to mitigate PFAS impacts on drinking water wells. It showed that relatively high levels of PFAS were found at depth, rendering well modification infeasible. The results indicated that wellhead treatment was the most robust mitigation strategy. This project highlighted the importance of profiling wells to better understand the extent of PFAS contamination at various depths and to inform decision-making for improving water quality.