PER- AND POLYFLUOROALKYL SUBSTANCE (PFAS) TRANSPORT FROM GROUNDWATER TO STREAMS NEAR A PFAS MANUFACTURING FACILITY IN NORTH CAROLINA, USA

PFAS are persistent environmental contaminants linked to multiple adverse health effects. In North Carolina, a chemical plant located in the Cape Fear River watershed has released PFAS into air and water for at least 4 decades. As a result, over 3,200 water supply wells are contaminated within a 16 km radius of the plant, and PFAS has contaminated the Cape Fear River, a drinking water source for about 250,000 people in downriver communities. The plant stopped directly discharging process wastewater to the Cape Fear River in November 2017, but ongoing discharge of contaminated groundwater into the river and its tributary streams could have long-term impacts on the river as a drinking water source.

The objectives of this study were to determine 1) how fast PFAS come out of the ground and into the streams and 2) how long it will take for PFAS to flush out of the groundwater system.Using hydrologic and PFAS concentration data, we quantified the discharge rate of PFAS from groundwater to five tributary streams of the Cape Fear River near the chemical plant.We used two different field approaches: 1) direct measurements of transport at the groundwater-stream interface (the streambeds), and 2) measurements in stream water.

Total quantified PFAS in groundwater was 20-4,773 ng/L (mean=1,863 ng/L, n=78); the range for stream water was 426-3,617 ng/L (mean=1,717 ng/L, n=22). Eight PFAS constituted 98% of total quantified PFAS; PMPA and GenX accounted for 61%. For PFAS discharge from groundwater to one stream, values estimated from stream water measurements (18 kg/yr) agreed fairly well with those from streambed measurements (22-25 kg/yr). Normalized by watershed area, this PFAS discharge was 10-10,000x larger than values reported from some rivers in Europe and India. Considering all five streams, about 32 kg/yr of total PFAS discharge from groundwater at baseflow and reach the Cape Fear River. The absence of PFAS-free groundwater and the time between first PFAS release and our sampling (39-48 yr) seem consistent with a roughly two-decade timescale for flushing of PFAS from the aquifer to streams, though more work is needed.

Discharge of contaminated groundwater to streams is a significant pathway for off-site migration of PFAS, which may lead to long-term contamination of surface waters and impact the water supply of downstream communities.