Leaching of PFOS and PFBS to groundwater at US Air Force bases: Could biochar offer an effective mitigation strategy?

Authors: Ashworth, Daniel; RAMOS, PIA - Gsi Environmental Inc; Schmidt, Michael; Ibekwe, Abasiofiok

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2026
Publication Date: 2/4/2026
Citation: Ashworth, D.J., Ramos, P., Schmidt, M.P., Ibekwe, A.M. 2026. Leaching of PFOS and PFBS to groundwater at US Air Force bases: Could biochar offer an effective mitigation strategy? Environmental Science and Technology. 60(6):5053-5062. https://doi.org/10.1021/acs.est.5c12996.
DOI: https://doi.org/10.1021/acs.est.5c12996

Interpretive Summary: The use of aqueous film forming foams (AFFFs) for extinguishing fires at military bases potentially leads to the contamination of soils by per- and poly-fluoroalkyl substances (PFAS). These compounds can be highly mobile and may move through soil to contaminate groundwater that may be used as a drinking or irrigation water resource. In this work, published data from US Air Force bases was analyzed to demonstrate that high levels of soil and groundwater PFAS contamination at such sites is common, particularly in fire testing and training areas, suggesting that prevention of PFAS leaching from such soils is a critical priority. Laboratory soil column experiments were then conducted to assess the use of biochars as a low-cost strategy for adsorbing two common PFAS compounds found in AFFFs, perfluorooctane sulfonic acid (PFOS) and perfluorobutane sulfonic acid (PFBS), and preventing their leaching from contaminated soil. Biochar is a carbon rich material that is made from burning waste biomass materials in the absence of oxygen; its physical and chemical properties mean that it can strongly adsorb organic molecules such as PFAS. We found that the application of carefully selected biochars to soil with high levels of PFAS contamination may be a useful and low-cost approach for preventing PFOS and PFBS (and potentially other PFAS) contamination of groundwater.

Technical Abstract: The use of aqueous film forming foams (AFFFs) at military bases potentially leads to the contamination of soils by per- and poly-fluoroalkyl substances (PFAS). These compounds can be highly mobile and leach through soil to contaminate groundwater that may be used as a drinking or irrigation water resource. In this work, a simple meta-analysis of data from US Air Force bases was conducted to demonstrate that high levels of soil and groundwater PFAS contamination at such sites is common, particularly in testing and training areas, suggesting that prevention of PFAS leaching from such soils is a critical priority. Soil column experiments were then conducted to assess the use of biochars as a low-cost strategy for adsorbing the PFAS compounds perfluorooctane sulfonic acid (PFOS) and perfluorobutane sulfonic acid (PFBS) and preventing their leaching from contaminated soil. A wood-based biochar produced at >900 °C added to the soil at 1% (m/m) was found to exhibit physio-chemical properties (high specific surface area, hydrophobicity, aromaticity, and polarity) that facilitated excellent (> 99%) retention of PFOS in a sandy loam soil. While this non-modified biochar did not yield the same high level of (short-chain) PFBS retention, post-production thermal treatment (400 °C in air) of the biochar markedly improved PFBS retention, essentially yielding non-detectable PFBS levels in the column leachate. The application of carefully selected biochars to areas with high levels of PFAS contamination at military facilities may be a useful and low-cost approach for mitigating PFOS and PFBS (and potentially other PFAS) leaching to groundwater.