Capillary Fringe Effects on Volatile Organic Compound Transport from the Vadose Zone into Groundwater
EMSL Project ID
47929
Abstract
Soil vapor extraction (SVE) is the prevalent remediation approach for volatile organic contaminants in the vadose zone in the US, including at Department of Energy contaminated sites. A general, user-friendly Microsoft Excel-based computational tool (SVEET; Soil Vapor Extraction Endstate Tool) was recently developed to estimate the impact of volatile organic contaminant (VOC) sources in the vadose zone on groundwater concentrations for sites where vapor-phase transport dominates. The tool provides an evaluation to determine whether vadose zone contamination has been diminished sufficiently, and is specifically designed to help field practitioners and site managers to determine an appropriate endpoint for SVE applications. The new tool is based on interpolation of results from a series of pre-modeled scenarios using the STOMP multiphase simulator. The large number of three-dimensional numerical simulations was conducted to evaluate the impact of several controlling factors on transport of VOCs into groundwater. The tested factors were source concentration, Henry's Law constant, well screen length, recharge, groundwater velocity, vadose zone thickness, as well as source dimensions and location.A project peer review panel concluded that, in general, the new estimation tool was based on sound scientific principles and that the multiphase scenario simulations were conducted properly. However, the reviewers expressed concern about the way mass transport across the capillary fringe (i.e., the zone above the water table under negative pressure holding water at full saturation) was conceptualized in the numerical model. Although the used assumption, i.e., minimization of the vertical dimension of the capillary fringe and maximizing contaminant transport into the groundwater, is convenient for a direct comparison of the various considered scenarios, it may not be consistent with field conditions and may lead to inaccurate predictions.
The panel therefore strongly recommended conducting detailed and quantitative intermediate scale experiments to investigate the role of the capillary fringe in transporting dissolved VOCs from the unsaturated zone into the moving groundwater. In this Science Theme proposal, intermediate-scale flow cell experiments are described that directly address the panel's recommendation. The experiments use EMSL's unique VOC resistant flow cells, a dual-energy gamma radiation system, and advanced data acquisition equipment.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2013-10-01
End Date
2014-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Yang S, M Oostrom, MJ Truex, G Li, and L Zhong. 2016. "Injectable Silica–Permanganate Gel as a Slow-Release MnO4? Source for Groundwater Remediation: Rheological Properties and Release Dynamics." Environmental Science Processes & Impacts 18(2):256-264. doi:10.1039/C5EM00559K