Analysis of Soil Vapor Extraction Data to Evaluate Mass‐Transfer Constraints and Estimate Source‐Zone Mass Flux

Abstract

Methods are developed to use data collected during cyclic operation of soil vapor extraction (SVE) systems to help characterize the magnitudes and timescales of mass flux associated with vadose zone contaminant sources. Operational data collected at the Department of Energy’s Hanford site are used to illustrate the use of such data. An analysis was conducted of carbon tetrachloride vapor concentrations collected during and between SVE operations. The objective of the analysis was to evaluate changes in concentrations measured during periods of operation and non-operation of SVE, with a focus on quantifying temporal dynamics of the vadose zone contaminant mass flux, and associated source strength. Three mass-flux terms, representing mass flux during the initial period of a SVE cycle, during the asymptotic period of a cycle, and during the rebound period, were calculated and compared. It was shown that it is possible to use the data to estimate time frames for effective operation of an SVE system if a sufficient set of historical cyclic operational data exists. This information could then be used to help evaluate changes in SVE operations, including system closure. The mass-flux data would also be useful for risk assessments of the impact of vadose-zone sources on groundwater contamination or vapor intrusion.

Non-aqueous phase liquid-contaminated soil remediation by ex situ dielectric barrier discharge plasma

“…Aqueous solutions may be injected for the purposes of flushing or to promote the in situ degradation of contaminants (Barcelona and Xie 2001;Devlin et al 2004). Most of the soil remediation technologies have a limited NAPL removal efficiency due to the retention of pollutants in low-permeability zones (e.g., soil vapor extraction) (Brusseau et al 2010;Carroll et al 2012) applicable to source zones composed of volatile organic contaminants (e.g., air sparging, supersaturated water injection) (Nelson et al 2009;Adams et al 2011). Only incineration, smoldering combustion, bio-treatment and chemical oxidation may transform contaminants to less toxic or non-hazardous species (Gierczak et al 2006;Switzer et al 2009;Ko et al 2012;Cai et al 2012).…”

Field-scale solute transport parameters derived from tracer tests in large undisturbed soil columns

“…Remediation of shallow and deep vadose zones contaminated by organic and inorganic substances often depends on the success of delivery of surface-applied or injected amendments into the vadose zone. Field-scale solute transport modelling is indispensable for evaluating the feasibility of such clean-up methods (Brusseau et al 2010;Zhang et al 2012). However, field-scale solute transport is significantly influenced by the heterogeneous nature of flow and transport properties across the field (Jacques et al 1998;Seuntjens et al 2002;Mallants et al 2011;Stauffer and Lu 2012).…”

Treatability Test Report: Characterization of Vadose Zone Carbon Tetrachloride Source Strength Using Tomographic Methods at the 216-Z-9 Site

“…The first element involved collecting data during the period of standard SVE system operation from March through August 2011 to quantify the SVE performance parameters as described by Brusseau et al (2010). These data were used to append the data set quantifying SVE system performance over the previous 15 years where the SVE system has been operated in a cyclic mode.…”

“…The DOE Office of Groundwater and Soil Remediation (EM-32) program has developed approaches for characterizing volatile contaminants, such as CT, in the vadose zone and evaluating their impact on groundwater (Truex et al 2009;Oostrom et al 2010;Brusseau et al 2010;Carroll et al 2012). These approaches and related ongoing EM-32 development efforts are the technical basis for evaluation of treatability test results.…”

“…For example, the Z-9 Trench SVE operation from 1993 to 1996 was highly effective, and removed several thousand kilograms of CT before the concentrations and mass removal rate substantially decreased. From 1997 through the present, cyclic operation has been applied to allow vapor concentration rebounding due to diffusive-mass transfer from low-permeability source zones (Rohay 2007;Brusseau et al 2010). …”