Quality Assurance in Soil Gas Surveys: False Positive Acetone Identifications at a Codisposal Site

Abstract

This paper points out the importance of quality assurance in soil gas surveys through the implementation of quality control measures. A soil gas survey was undertaken at the Cortese Landfill to assess vapor migration. Soil gas samples were analyzed from 54 locations for 15 volatile organic compounds by gas chromatograph (GC) methods. Quality control measures included GC calibration, replicate, spike and blank samples and analysis of split samples by an off site analytical lab. Acetone was detected at many of the soil gas sample locations at unexplainable concentrations relative to concentrations observed in groundwater. A second GC, equipped with a different column, was used to confirm presence of acetone, but at concentrations lower than those estimated using the first column. This indicated that coeluting compounds may have caused false positive results (misidentifications) in the earlier data. This approach to verification of field analytical data quality assurance proved to be beneficial in preventing costly additional sampling and analysis.

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“…Soil gas analysis consists of collecting and analyzing headspace vapors for the presence of organic contaminants in subsurface soil samples. Soil gas methods are often used in preliminary site characterization studies and provide immediate data at a lower cost than other conventional subsurface sampling and chemical analysis techniques (Heins, et al 1992). Soil gas surveying is useful for detecting a wide range of VOCs at ppm levels under a variety of geologic and hydrologic environments.…”