Methodology for Analyzing Soil Vacuum Data at VOC-Contaminated Sites

Proper design of a soil vapor extraction (SVE) treatment system at a site contaminated with volatile organic compounds (VOCs) hinges on the effective characterization of vapor flow through the subsurface. The collection and analysis of soil vacuum data during vapor extraction provides the basis for this characterization. Although the collection of soil vacuum data is routinely performed across the industry at VOC-contaminated sites, a systematic and quantitative method of analyzing vacuum data typically is not employed. Thus a comprehensive analysis is presented for the characterization of vapor flow through the subsurface. This methodology includes: (1) the interpretation of vacuum data using statistical analysis to infer site stratigraphy and soil permeability; (2) diagnosis of vapor flow “short circuits”; and (3) flow path mapping. The statistical analysis includes the determination of the 95% confidence intervals of the collected SVE data. The confidence intervals are used to determine if deviations of individual data points from the linear trend are statistically significant. Once a region of homogeneity is delineated through the statistical analysis, flow net construction is performed. Case studies are presented to demonstrate how vacuum data is used to characterize subsurface vapor flow and to discuss the SVE design implications of these characterizations.