Analysis of Water Saturation, NAPL Content, Degradation Half-Life, and Lower Boundary Conditions on VOC Transport Modeling: Implications for Closure of Soil Venting Systems |
| |
| Authors: | Dominic C DiGiulio Ravi Varadhan |
| |
| Institution: | Dominic C. DiGiulio (U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Subsurface Protection and Remediation Division, Ada, OK 74820) received a B.S. in environmental engineering from Temple University, an M.S. in environmental science from Drexel University in Philadelphia, and a Ph.D. in soil, water, and environmental science from the University of Arizona. He served as a Superfund remedial project manager in U.S. EPA, Region III in Philadelphia for six years. He has provided technical assistance and conducted research in soil venting and air sparging for the last 13 years.;Ravi Varadhan (School of Public Health, Johns Hopkins University, Baltimore, Maryland) served as an environmental engineer with the Dynamac Corp. in Ada, Oklahoma, for seven years. His responsibilities included providing technical assistance and technology support to various U.S. EPA regional offices. He holds a B.S. in chemical engineering and a Ph.D. in environmental engineering. |
| |
| Abstract: | Simulations using a one-dimensional, analytical, vadose zone, solute-transport screening code (VFLUX) were conducted to assess the effect of water saturation, NAPL saturation, degradation half-life, and boundary conditions at the vadose zone/ground water interface on model output. At high initial soil concentrations, model output was significantly affected by input parameters and lower boundary conditions yet still resulted in consistent decision-making to initiate or continue venting application. At lower soil concentrations, however, typical of what is observed after prolonged venting application, differences in model input and selection of lower boundary conditions resulted in inconsistent decision-making. Specifically, under conditions of low water saturation, use of a first-type, time-dependent lower boundary condition indicated that the primary direction of mass flux was from ground water to the vadose zone, suggesting little benefit from continued venting application. Use of a finite, zero-gradient lower boundary condition, though, indicated continued mass flux from the vadose zone to ground water, suggesting a continued need for venting application. In this situation, sensitivity analysis of input parameters, selection of boundary conditions, and consideration of overall objectives in vadose zone modeling become critical in regulatory decision-making. |
| |
| Keywords: | |
|
|
