An alternative approach for characterization of sites contaminated by volatile organic compounds (VOCs) has been employed at Sandia National Laboratories, Albuquerque, New Mexico (SNL/NM), in order to characterize a plume from a chemical waste landfill (CWL). The characterization approach is designed to maximize the use of soil gas analysis for definition of the nature and extent of contamination and for validation of the conceptual model of contaminant transport. Comparison of the soil gas data analyzed at an on-site laboratory with those data generated by an EPA-approved analytical laboratory indicates that soil gas data provide a much more representative picture of site conditions. To assist in the validation of our conceptual model of contaminant transport for the CWL, we employed an approach developed at SNL/NM that allows for assessment of nonaqueous phase liquids (NAPLs) through equilibrium testing of the soil gas data.
Ground water beneath the CWL, approximately 146 m below ground surface (BGS), has been impacted by low levels of VOCs. Laboratory data from soil samples collected through split-spoon sampling techniques revealed detectable contaminants to a maximum depth of approximately 6 m BGS. However, soil gas concentrations revealed a contaminant plume at concentrations in the range of 100 ppmv at depths greater than 60 m BGS. We demonstrate in this paper that soil gas data can provide a much more accurate picture of site conditions.