Perfluoroalkyl and polyfluoroalkyl substances (PFAS) in groundwater at a reclaimed water recharge facility

Reclaimed water is becoming an increasingly important source of water in arid regions worldwide. In the City of Tucson, Arizona, reclaimed water comprises approximately 10% of the annual water supply. It is used to recharge the local aquifer, create surface flow in the Santa Cruz River, and irrigate parks, golf courses, and recreational fields. In December 2018, concentrations of perfluoroalkyl and polyfluoroalkyl substances (PFAS) an order of magnitude higher than the EPA lifetime health advisory of 70 ppt were discovered in the city's reclaimed water system. The PFAS were also detected in the Sweetwater Recharge Facility (SRF), adjacent to the Santa Cruz River, where reclaimed water is stored in the alluvial aquifer. PFAS have gained national attention as contaminants of emerging concern because of their widespread occurrence, toxicological impact to humans, and persistence in the environment. However, relatively little is known about their fate and transport in managed aquifer recharge systems. Results from this study show that PFAS in the SRF likely originated from the city's retired wastewater treatment facility, while lower PFAS concentrations are observed in the treated wastewater provided by the city's new treatment facility. Moreover, the combined PFOS and PFOA concentrations appear to be correlated to rising and falling groundwater levels, indicating that PFAS are likely trapped in the vadose zone and transported to the alluvial aquifer during managed aquifer recharge events.