Hydrogeologic Drivers and Management Implications of PFAS, Nitrate, and Pharmaceuticals in Groundwater at a Karst Beneficial Reuse System

Abstract

Management of beneficial reuse sites typically focuses on controlling the fate and transport of conventional water quality parameters, particularly nitrogen. However, it is unclear if current management is also effective for controlling contaminants with distinct physiochemical properties, such as pharmaceuticals and per- and polyfluoroalkyl substances (PFAS). We investigated the spatial and temporal patterns of nitrate, PFAS, and pharmaceuticals in groundwater monitoring wells at a beneficial reuse site. These data sets were integrated with hydrogeologic variables, including groundwater elevation, rainfall, surface karst features, wastewater inputs, and irrigation intensity, to compare drivers of occurrence, fate, and transport behavior across classes of contaminants. Additionally, we evaluated the suitability of a modified version of a groundwater vulnerability model for predicting spatial patterns of PFAS and pharmaceuticals. Overall, pharmaceuticals exhibited lower detection frequencies, higher temporal variability, and spatial patterns distinct from nitrate and PFAS. Their episodic occurrence responded strongly to wastewater inputs and rarely exceeded criteria for antibiotic resistance. In contrast, PFAS and nitrate concentrations fluctuated primarily with groundwater elevation and were well-aligned with groundwater vulnerability predictions. Results suggest that reuse management should target periods of high rainfall and consumer use to reduce pharmaceutical inputs, whereas nitrate and PFAS management should be informed by groundwater conditions.