Evaluation of Mass Flux to and from Ground Water Using a Vertical Flux Model (VFLUX): Application to the Soil Vacuum Extraction Closure Problem

Authors

  • Dominic C. DiGiulio,

    1. Dominic C. DiGiulio (U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Robert S. Kerr Environmental Research Center, 919 Kerr Research Dr., Ada, OK 74820) received his B.S. degree in environmental engineering at Temple University and M.S. degree in environmental science at Drexel University in Philadelphia, Pennsylvania. He served as a regional project manager (RPM) in U.S. EPA Region III in Philadelphia for six years. He has provided technical assistance to RPMs and conducted research in soil vacuum extraction and air sparging at the Robert S. Kerr Environmental Research Center for the past 11 years. Comments on this paper should be directed to him at digiulio.dominic@epamail.epa.gov.
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  • Varadhan Ravi,

    1. Dr. Varadhan Ravi has been with Dynamac Corp. in Ada, Oklahoma, for more than seven years as an environmental engineer. His responsibilities include providing technical assistance and technology support to the various EPA regional offices, through the National Risk Management and Research Laboratory, Ada, Oklahoma. He holds a bachelor's degree in chemical engineering and a doctoral degree in environmental engineering. His primary interests lie in the application of deterministic and stochastic mathematical methods to the analysis of subsurface problems.
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  • Mark L. Brusseau

    1. Dr. Mark L. Brusseau is a professor in the Departments of Soil, Water and Environmental Science, and Hydrology and Water Resources at the University of Arizona. His research is focused on developing a fundamental understanding of the factors and processes influencing the transport, fate, and remediation of chemicals in the subsurface. He is also interested in the development and evaluation of innovative methods for characterization and remediation of subsurface contamination, and the evaluation of risks posed to human health by contamination. He is or has been the principal or co-principal investigator for more than 25 research projects, with a combined budget of more than $9 million. He has received the EXXON Foundation Environmental Research Award, the National Academy of Sciences Young Investigator Award, the U.S. Department of Energy Distinguished Young Faculty Award, and has held Research Fellow appointments with the U.S. Department of Energy and the U.S. Air Force.
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Abstract

Site closure for soil vacuum extraction (SVE) application typically requires attainment or specified soil concentration standards based on the premise that mass flux from the vadose zone to ground water not result in levels exceeding maximum contaminant levels (MCLs). Unfortunately, realization of MCLs in ground water may not be attainable at many sites. This results in soil remediation efforts that may be in excess of what is necessary for future protection of ground water and soil remediation goals which often cannot be achieved within a reasonable time period. Soil venting practitioners have attempted to circumvent these problems by basing closure on some predefined percent total mass removal, or an approach to a vapor concentration asymptote. These approaches, however, are subjective and influenced by venting design. We propose an alternative strategy based on evaluation of five components: (1) site characterization, (2) design. (3) performance monitoring, (4) rule-limited vapor transport, and (5) mass flux to and from ground water. Demonstration of closure is dependent on satisfactory assessment of all five components. The focus of this paper is to support mass flux evaluation. We present a plan based on monitoring of three subsurface zones and develop an analytical one-dimensional vertical flux model we term VFLUX. VFLUX is a significant improvement over the well-known numerical one-dimensional model. VLEACH, which is often used for estimation of mass flux to ground water, because it allows for the presence of nonaqueous phase liquids (NAPLs) in soil, degradation, and a lime-dependent boundary condition at the water table inter-face. The time-dependent boundary condition is the center-piece of our mass flux approach because it dynamically links performance of ground water remediation lo SVE closure. Progress or lack of progress in ground water remediation results in either increasingly or decreasingly stringent closure requirements, respectively.

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