Airports as Major AFFF Discharge Sites
Commercial airports are among the highest-volume AFFF users outside of military installations. Federal Aviation Administration requirements mandate AFFF stockpiling and rapid deployment capability at certificated airports, and periodic testing of delivery systems has historically required foam discharge to the environment. Aircraft rescue and fire-fighting (ARFF) training programs at airports generated recurring small-volume AFFF discharges that accumulated in soils around fire-training areas, ramp runoff collection ponds, and stormwater retention infrastructure. Airports near population centers have become significant point sources of PFAS contamination to adjacent groundwater and surface water.
The AFFF chemistry at commercial airports reflects the same fluorotelomer-dominated formulations used across the civil aviation industry. This means that airport-associated PFAS contamination tends to be particularly rich in fluorotelomer sulfonates (4:2 FTSA, 6:2 FTSA, 8:2 FTSA) and fluorotelomer alcohols (FTOHs) — compounds classified as PFAS precursors because they oxidize to PFCAs in the environment. The presence of these precursors in airport runoff and groundwater creates a treatment challenge that differs fundamentally from sites where legacy PFOS and PFOA are the primary contaminants.
The Precursor Problem: Compounds That GAC Ignores
PFAS precursors — FTSAs, FTOHs, perfluoroalkyl sulfonamides (FOSA), and fluorotelomer-based phosphate esters — are not currently regulated under the EPA NPDWR, and most PFAS monitoring programs do not include them in standard analytical panels. They are therefore invisible to treatment systems designed and monitored for regulated PFAS compound removal. Yet these precursors are biologically significant: oxidative transformation in the environment, in drinking water distribution systems, and in the human body converts FTSAs and FTOHs into PFCAs that are regulated compounds.
GAC has limited adsorption affinity for many precursor compounds. FTOHs are relatively volatile and may partition to the gas phase rather than adsorbing to the carbon surface. Ionic FTSAs have some adsorption affinity but are generally less strongly adsorbed than PFOS or PFOA due to their structural differences. The practical consequence for airport-adjacent communities is that a GAC-based treatment system certified for PFOS and PFOA removal may have little effect on the precursor PFAS that constitute a large fraction of total fluorochemical exposure at these sites.
Precursor Oxidation in Distribution Systems
Chlorination of drinking water — a universal disinfection practice in municipal systems — can oxidize PFAS precursor compounds to PFCAs in the distribution system. This means that source water entering a treatment plant with low measured concentrations of regulated PFCAs but high precursor loading can generate regulated PFAS within the distribution system downstream of the treatment step. A treatment system that measures inlet and outlet concentrations of regulated PFAS will appear to perform well while the precursor-to-PFCA conversion continues to occur in finished water.
Total oxidizable precursor (TOP) assay is an analytical method that quantifies the pool of PFAS precursors in a water sample by converting them to measurable PFCAs through strong chemical oxidation. Using TOP assay data alongside conventional PFAS measurements provides a more complete picture of total fluorochemical exposure. For airports and other AFFF-impacted sites, the difference between measured PFAS and TOP-assay PFAS can be substantial, revealing a precursor loading that standard treatment may not address.
Broad-Spectrum Media for Precursor-Rich Source Waters
PFAS-selective adsorbent media that provides effective removal of both regulated PFAS compounds and their precursors represents the most complete treatment approach for airport-impacted source water. The adsorption mechanism in advanced PFAS-selective media — which targets the fluorinated carbon tail present in all PFAS and PFAS precursor structures — provides a structural basis for precursor removal that is less dependent on the specific ionic character of each target compound.
Pilot data from airport-adjacent treatment sites that have used TOP assay monitoring to track both regulated PFAS and precursor removal show that PFAS-selective media achieves measurably higher total fluorochemical reduction than GAC alone. This broader removal reduces the concentration of precursors available for in-distribution conversion to regulated PFCAs, providing an additional public health benefit that conventional PFAS monitoring alone would not capture.