Development of a Decision Support Tool for Vadose Zone Remediation of Volatile Contaminants

Jennifer Segura | NAVFAC EXWC

ER-201731

Objective

The objective of this project is 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. The project aims to expand, test, and demonstrate 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.

ER-201731_graphic

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Technology Description

The project will expand upon the existing technology encapsulated in the SVEET software (Truex et al., 20131; Oostrom et al., 2014). Previous U.S. Department of Energy (DOE) efforts resulted in a guidance document on soil vapor extraction (SVE) optimization, transition, and closure (Truex et al., 2013), which included the SVEET software. SVEET, in its current form, is an easy-to-use spreadsheet tool that facilitates estimating the impact of a vadose zone contaminant source on groundwater contaminant concentrations. SVEET needs only a small number of user inputs, which are often already available as part of existing site data, but which can be cost-effectively obtained, if needed. SVEET is, however, currently limited in the range of site conditions it can address, and does not address vapor intrusion (VI).

SVEET provides defensible information to support decisions about the need for remediation or the endpoints of remediation. SVEET software results are derived from about a thousand rigorous simulations of three-dimensional, multi-phase contaminant transport under natural conditions conducted using the Subsurface Transport over Multiple Phase (STOMP) code on the DOE’s high-performance computing resources. These simulations include recharge-driven processes, vapor-phase processes, and mixing into the groundwater, all demonstrated to be important for estimating contaminant transport. This capability is not available in other common tools such as Vadose Zone Leaching (VLEACH). Thus, SVEET provides a more defensible estimate of contaminant transport as a basis for supporting remedy decisions. As a component of a previous ESTCP project ( ER-201125), a tool related to SVEET was published (Vapor Intrusion Estimation Tool for Unsaturated-Zone Contaminant Sources [VIETUS]) that enabled assessment of VI for a limited set of conditions.

SVEET currently has limitations for DoD application because it was developed for DOE-relevant site conditions. This project focuses on expanding the breadth of allowable site conditions to broaden applicability at DoD sites. Updates, entailing 5000-7000 new simulations, will include expanding the range of inputs for vadose zone thickness, source configuration, moisture conditions, and contaminant options, as well as extending the output to include estimates of shallow soil vapor concentrations for VI analyses (integrating the core elements of the VIETUS software). Field demonstration for tool testing and to facilitate tool transfer also will be conducted. 

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Benefits

The tool 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. (Anticipated Project Completion - 2020)

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Points of Contact

Principal Investigator

Jennifer Segura

NAVFAC EXWC

Phone: 202-685-9336

Program Manager

Environmental Restoration

SERDP and ESTCP

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