A volatile organic compound (VOC) contamination source in the vadose zone presents a potential threat to underlying groundwater and/or to nearby structures through vapor intrusion. Soil vapor extraction (SVE) is a commonly applied remediation technology to address VOC contamination in the unsaturated zone. SVE performance assessment guidance provides a structured approach to evaluate whether the SVE system should be terminated, optimized, supplemented, or transitioned to an alternative remedial approach. The ability to quantify impacts of the remaining source area on groundwater and soil gas are critical to a performance assessment in support of such remedial decisions. The objective of this project was to provide the Department of Defense (DoD) with a widely applicable tool for determining the initial or continued need for vadose zone volatile organic compound (VOC) remediation to be protective of groundwater and to prevent vapor intrusion problems. Under this project, the Soil Vapor Extraction Endstate Tool (SVEET), a user-friendly spreadsheet that provides concentration estimates to support decisions on starting, closing, or altering vadose zone remediation, was expanded, tested, and demonstrated.
The Soil Vapor Extraction Endstate Tool version 2 (SVEET2) is an updated version of the SVEET spreadsheet software for estimating contaminant concentrations in groundwater and soil gas that are caused by a vadose zone contaminant source. SVEET2 has a rigorous basis from numerical model simulations for a generalized conceptual model that cover a set of parameters and contaminants that are relevant to a wider variety of sites than SVEET version 1.0. The software update includes results from over 5500 numerical simulations to provide these expanded options for site applicability. SVEET2 itself is not a numerical model; rather, it interpolates between premodeled scenario numerical simulation results and scales those results for parameters with linear relationship.
SVEET2 allows for a wider range of sites to be represented (compared to SVEET v. 1.0), including more than 93% of surveyed DoD sites. A demonstration of the SVEET2 software was performed for the purpose of model verification and obtaining user feedback about software applicability. While it is challenging to find suitable sites for rigorous ground-truthing, several sites were suitable for use in the demonstration.
The ground-truthing had a mixture of results, with 77% of test cases with results that were on par with observed field data or were conservative estimates with respect to decision making (i.e., would be protective relevant to cleanup goals), and the remaining 23% of test cases less than, but within a factor of 2-3, of the observed field data. Overall, the software was found to be user friendly and applicable for many of the tested field sites. Technology transfer activities (though constrained by the COVID pandemic) were included in the project to publicize the software capabilities and provide users with insight on software use.
The outcome of this project is a tool that uses readily available site information and that will allow DoD users to easily assess the initial or continued need for vadose zone remediation with respect to being protective of groundwater and preventing vapor intrusion problems. Such assessment supports remediation decisions and can significantly reduce DoD's cost to complete remediation. The tool is applicable to any vadose zone contamination, even if another source to groundwater exists (e.g., sites where DNAPL has migrated into groundwater). The SVEET tool will allow evaluation of vadose zone remedies independently of groundwater, even though the need may exist for separate groundwater remediation. The ability to quickly estimate the impact of vadose zone VOC sources on groundwater and potential vapor intrusion will allow DoD users to determine the need for vadose zone remediation and the endpoint for remediation. DoD users will better be able to 1) focus limited remediation funds on sites where treatment will provide a benefit and 2) more rapidly close sites where remediation is no longer required.
Johnson, C.D., K.A. Muller, M.J. Truex, G. Tartakovsky, D.J. Becker, C.M. Harms, and J. Popovic. 2021. A Rapid Decision Support Tool for Estimating Impacts of a Vadose Zone Volatile Organic Compound Source on Groundwater and Soil Gas. Groundwater Monitoring & Remediation, http://doi.org/10.1111/gwmr.12468