Reactive Core Matting ( <scp>RCM</scp> ) to Passively Treat <scp>PFAS</scp> ‐Impacted Groundwater Discharging to a Small Stream

Abstract Groundwater near a former fire training area (FTA) discharges to a nearby small perennial stream and is impacted by per‐ and polyfluoroalkyl substances (PFAS), including (generally listed in order from highest to lowest concentrations): perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexanesulfonic acid (PFHxS), perfluorohexanoic acid (PFHxA), perfluorobutanesulfonic acid (PFBS), and perfluorobutanoic acid (PFBA). Upstream of the FTA, total PFAS (i.e., the sum of PFAS measured by United States Environmental Protection Agency [USEPA] Method 537.1, or Σ 24 PFAS) concentrations in the stream are about 10,000 ng/L resulting from various other PFAS sources, however, after passing by a 400‐feet long reach adjacent to the FTA, in‐stream Σ 24 PFAS concentration increase by an average of about 15,000 ng/L as a result of the discharge of impacted groundwater (the average Σ 24 PFAS mass discharge from groundwater is estimated at about 5.0 g/d. Reactive core matting (RCM) consisting of adsorptive media (FLUORO‐SORB ® 200) woven between two layers of permeable geo‐fabric was installed along a targeted reach of the stream to passively remove PFAS from discharging groundwater. Nine quarterly performance monitoring events, which included measurements of streamflow, and porewater and surface water concentrations, were conducted over a 2.4‐year performance period. The RCM was highly successful in reducing Σ 24 PFAS mass discharging from groundwater to the stream, removing an estimated 8.2 kg of Σ 24 PFAS, which represents nearly all PFAS mass discharging from groundwater. The stream treatment values (calculated from the increase in concentration over the reach after RCM installation compared to baseline) were relatively high and consistent, all averaging over 80%. However, some PFAS (notably PFBA, PFBS, PFHxA, and PFHxS) show a slight decline in stream treatment values for the last two monitoring events, possibly indicating treatment efficiency may have begun to decline for these specific PFAS. This work highlights both the practical implementability and efficacy of this technology, and therefore, RCMs are recommended for consideration at other similar PFAS‐impacted sites.