Tool and Database for Estimating Potential Longevity of Colloidal Activated Carbon Barriers for PFAS in Groundwater

ABSTRACT This study presents a planning‐level graphical tool and a regression equation model for estimating the longevity of Colloidal Activated Carbon (CAC) barriers for treating per‐ and polyfluoroalkyl substances (PFAS) in groundwater. The tool development incorporated information from field‐scale CAC barriers, including design data from 17 sites and performance monitoring results from a total of 26 sites. The tool consists of both graphical and mathematical frameworks for estimating barrier longevity based on site‐specific parameters, including barrier dimensions, groundwater Darcy velocity, CAC loading, and influent PFAS concentrations. Application of the tool to 17 field sites yields barrier longevities ranging from 4 to over 100,000 years, with median values of 870, 150, and 180 years for PFOS, PFOA, and PFHxS, respectively. The wide variation in longevities is partly due to the significant variability in PFAS mass flux entering the barriers, as shown by the five‐order‐of‐magnitude difference in PFOA mass flux, ranging from 4 × 10 −8 to 1 × 10 −3 kg m −2 year −1 . The systematic decrease in barrier longevity from PFOS to PFOA/PFHxS aligns with known sorption behavior of these compounds onto CAC media. Key uncertainties in longevity estimation include spatial and temporal variability of PFAS and CAC, hydrogeologic heterogeneity, sorption isotherm selection, competitive sorption effects, and limited long‐term performance data. The tool provides a standardized approach for preliminary barrier design using site‐specific data while emphasizing the importance of applying appropriate safety factors and implementing long‐term monitoring strategies.