C.1.2.3 Landfill DU Characterization

As part of the site investigation, USCG took the opportunity to evaluate the potential advantage and limitations of incremental sampling methodology (ISM) approaches over traditional, discrete sampling approaches. More than 600 discrete samples were collected from within the landfill footprint. Splits of the discrete samples were combined and used to prepare ISM samples for targeted areas and depth intervals.

A 10-foot spaced sampling grid was initially established across the entire landfill footprint (see Figure C.1-4). Three depth intervals were targeted for characterization: 0–4 inches (152 samples), 28–36 inches (128 samples), and 36–60 inches (128 samples). A split sample or increment was randomly collected from each discrete sample. Increments for targeted areas and depth intervals were combined into a single ISM sample for that interval. Triplicate ISM samples were prepared for the 36–60 inch interval, for a total of five ISM samples for the DU as a whole.

Ten-foot and five-foot sampling grids used in 2008 ISM study.

Figure C.1-4. Ten-foot and five-foot sampling grids used in 2008 ISM study.
Source: USCG 2009, Figure 3-1.

Each ISM sample was air-dried and passed through a 2 mm (#10) sieve to remove larger particles. An aliquot was prepared by collecting and combining thirty 1 g increments of soil from a sample. The aliquot was tested for PCBs using a RaPID Assay Immunoassay field kit. Splits of discrete samples submitted to a laboratory for gas chromatograph analysis indicated good correlation with the immunoassay field kit data.