Formatted Title
Investigation and Remediation of AFFF, after Fire Department Training, at an Elementary School Sport's Field
Background/Objectives
A municipal fire department trained with aqueous film forming foams (AFFF) on an elementary school’s sports field. Investigation more than 10 years later identified that the soil (500 mg/Kg), groundwater (10- to 17,000 ng/L) and surface water (40 ng/L) had been impacted with PFAS (the sum of five analytes, PFOS, PFOA, PFNA, PFHxS, and PFHpA). The bedrock groundwater concentrations were approximately 600 ng/L below the source; however, adjacent bedrock water supply wells were below the State’s drinking water action levels. The object was to define the nature and extent of the PFAS and develop a remedial approach to mitigate exposure risks.
Approach/Activities
Soil characterization included SPLP and total PFAS analysis and an assessment of TOC. The total PFAS analyses identified a targeted area where the AFFF was applied to the field. The SPLP leachability data identified that the carboxylates (PFNA, PFHpA and PFHxA) leach more than the sulfonates (PFOS and PFHxS). However, the groundwater data beneath the source indicate that the concentration of PFOS (7,800 ng/L) was approximately the same as the sum of the three carboxylates (8,200 ng/L).
To assess the discharge into the surface water, monitoring wells were installed directly at the edge of the brook and just upgradient. The upgradient well screens were installed 10 feet into the water table, whereas the well screens adjacent to the brook were 2 feet in length at the water table. The concentration of PFAS in the upgradient wells was less than the concentration at the brook. This may be related to the fate and transport of the PFAS along the capillary fringe/water table interface (2-foot screen) such that the concentration directly at the water table are greater than the average across the 10-foot screen.
Results/Lessons Learned
Because of the evolving nature of the PFAS regulations, the selected final remedy had to accommodate potential future changes in regulatory criteria. The groundwater remedy includes a hydraulic control system to prevent future PFAS from migrating into the brook and design of a PFAS treatment system with a surface water discharge. The soil remedy looked at excavation and disposal of more than 8,000 cy of soil to the groundwater; however, it was determined that it was cost prohibitive and left a future potential CERCLA liability to the municipality. Soil stabilization and an impermeable engineered control (cap) were also considered. Based upon cost considerations, the engineered control was selected, and a new baseball/soccer field will be incorporated into the design.
If the remedial approach was implemented to early, additional work and costs would have been required/incurred because of the evolving/lowering of the regulatory PFAS criteria for soil and groundwater cleanup.