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Estimating the Impact of Vadose Zone Sources on Groundwater to Support Performance Assessment of Soil Vapor Extraction
Citation:
Oostrom, M., M. J. Truex, A. K. Rice, C. D. Johnson, K. C. Carroll, D. J. Becker, AND M. A. Simon. Estimating the Impact of Vadose Zone Sources on Groundwater to Support Performance Assessment of Soil Vapor Extraction. Groundwater Monitoring & Remediation. Wiley-Blackwell Publishing, Hoboken, NJ, 34(2):71-84, (2014).
Impact/Purpose:
To inform the public.
Description:
Soil vapor extraction (SVE) is a prevalent remediation approach for volatile contaminants in the vadose zone. To support selection of an appropriate endpoint for the SVE remedy, an evaluation is needed to determine whether vadose zone contamination has been diminished sufficiently to protect groundwater. When vapor-phase diffusive transport is an important component of the overall contaminant fate and transport from a vadose zone source, the contaminant concentration expected in groundwater is controlled by a limited set of parameters, including site specific dimensions, vadose zone properties, and source characteristics. A conceptual model demonstrating this approach is described in a companion paper (Oostrom et al. 2012; this issue). Based on that model, a framework was developed for estimating the contaminant concentration in groundwater resulting from a contaminant source in the vadose zone. The framework uses pre-modeled three-dimensional contaminant transport simulations results for a matrix of parameter value combinations covering a range of potential site conditions. An interpolation and scaling process are then applied to estimate contaminant concentrations at compliance (monitoring) wells for site-specific conditions. The framework has been incorporated into a user-friendly Microsoft® Excel®-based spreadsheet tool, which is made available to the public. The spreadsheet allows practitioners to avoid using a three-dimensional multiphase model and may also allow them to effectively assess parameter uncertainly by completing a sensitivity analysis. In many cases, the framework spreadsheet may be appropriate to consider the effect of a diminishing vadose zone source over time.
