C.1.2.4 Landfill DU ISM Results

Reported concentrations of PCBs in the 0–4 inch, 28–36 inch, and 36–60 inch interval ISM samples were 0.35, 2.5, and 40 mg/kg, respectively (see Figure C.1-5). Reported concentrations of PCBs in the two replicate samples collected from the lowermost interval were 36 and 34 mg/kg. Triplicate data suggested a minimal degree of combined field and laboratory error in the samples. This is not surprising, given the large number of increments (i.e., 128–152) collected from each interval.

Summary of ISM investigation results.

Figure C.1-5. Summary of ISM investigation results.
Source
: USCG 2009, Figure 4-1.

PCB data for each of the three targeted intervals indicated contamination above the USEPA Regional Screening Level of 0.22 mg/kg (USEPA 2008); the lower two intervals also exceeded the HDOH soil action level of 1.1 mg/kg (HDOH 2008a). Both of these screening levels are based on continuous, long-term human occupation of an area and are not necessarily applicable to current conditions on the remote, uninhabited atoll. Potential erosion of the former landfill area and dispersal of PCBs into adjacent aquatic habitats is considered to be the primary hazard posed by the contaminated soil. Reported concentrations of PCBs exceeded the marine sediment probably effects level of 0.709 mg/kg (CCME 2001, as referenced in Buchman 2008).