Historical aerials and previous reports showed indicated that between approximately 1953 and 1987 there were fire training areas in the vicinity of Darwin Road along the southwestern portion of the DCRA. These trainings utilized Aqueous Film Forming Foam (AFFF), which was primarily formulated with perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in addition to numerous accessory PFAS, as a fire suppressant. The objective of the SI was to determine the magnitude and extent of PFAS impacts to the soil and groundwater at the Site from previous fire training activities.

The SI consisted of the completion of 23 direct-push soil borings, and the installation of four groundwater-table monitoring wells and one deeper piezometer. Soil samples for laboratory analysis were collected from two discrete depth intervals above the water table at each soil boring location; one between 0 and 4 feet below grade (ft bg) and one generally between 10- and 13-ft bg. In addition, two rounds of groundwater samples were collected approximately 3 months apart from the monitoring wells and piezometer.

All soil borings completed during the SI had reported concentrations of PFAS above laboratory method detection limits (MDLs); with PFOA being reported above the Wisconsin Department of Natural Resources (WDNR) non-industrial direct contact Residual Contaminant Level (RCL) at one location. PFAS were reported above laboratory MDLs in the groundwater samples collected from all four water-table monitoring wells and the piezometer. PFOA, perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), and PFOS were detected in select groundwater samples collected above their respective Enforcement Standards (ESs) which are recommended by the Wisconsin Department of Health Services (DHS) to the WDNR.  

Spider plots were created for accessory PFAS to determine if there was any correlation between the occurrence of PFAS detected in soil and groundwater samples collected from the same location at shallow depths. Overall, the site does not show normal conventions for contaminant distribution in the subsurface soil, suggesting different possible sources and/or the different constituent make-up of fire-fighting foam over the years (1953-1987). Another possible explanation for this unconventional contaminant distribution is earth moving activities (e.g. re-grading, importing, and mixing of fill materials).  Based on results of the 2023 SI, the extent and magnitude has not been fully defined at the site.

Project Highlights

• Shannon & Wilson utilized historic aerial photography to pin-point areas of concern, increasing field efficiency and decreasing overall cost.
• Shannon & Wilson applied  spider plots to elucidate potential PFAS fate and transport between the local soil and groundwater, which helped illustrate  the extent and magnitude of PFAS at the site.