Distribution of PFOS in Groundwater from AFFF Storage, Handling, and Use

Discharge of aqueous film forming foam (AFFF), containing perfluorooctane sulfonate (PFOS), differs from typical mechanisms of contaminant release (inadvertent leaks and spills). Mechanisms include, 1) low volume spills of foam concentrate during storage or transfer; 2) one-off, high-volume, broadcast application of foam solution for firefighting; 3) periodic, moderate to high volume, broadcast application of foam solution for apparatus testing or training. AFFF is applied by mixing foam concentrate and water to make foam solution that is aerated when sprayed, producing finished foam. Thousands of gallons of foam solution may be applied for a fire or training event. Foam solution drains from the finished foam as an aqueous film with low surface tension that floats on fuel, facilitating soil infiltration and potential interaction with subsurface LNAPL.

PFOS concentrations >1,000 µg/L in shallow groundwater were measured beneath fire training and AFFF bulk storage areas compared to concentrations <50 µg/L beneath satellite AFFF storage, fire, and apparatus testing locations. Concentrations <20 µg/L were measured in groundwater beneath distal areas of runoff infiltration. PFOS soil concentrations also correspond to surface use: 16 mg/kg (bulk storage), 5.59 mg/kg (fire training), 1.57 mg/kg (satellite storage), 0.258 mg/kg (runoff channel). Shallow soil and groundwater concentrations are correlated by location (R² = 0.89), indicating PFOS in groundwater is largely a function of initial direct infiltration over broad areas versus prolonged migration in groundwater from a discrete source. Shallow soil concentrations represent a residual fingerprint of past infiltration to groundwater. More than a decade after AFFF was used at one facility, the migration distance of PFOS in groundwater remains much less than both the width of the soil fingerprint and the distal extent of groundwater impacts due to channelized runoff and infiltration.