You are here:
ANALYSIS OF WATER AND NAPL SATURATION, DEGRADATION HALF-LIFE, AND LOWER BOUNDARY CONDITIONS ON VOC TRANSPORT MODELING: IMPLICATIONS FOR SOIL VENTING CLOSURE
Citation:
DiGiulio*, D C. AND R. Varadhan. ANALYSIS OF WATER AND NAPL SATURATION, DEGRADATION HALF-LIFE, AND LOWER BOUNDARY CONDITIONS ON VOC TRANSPORT MODELING: IMPLICATIONS FOR SOIL VENTING CLOSURE. GROUNDWATER MONITORING AND REMEDIATION 21(4):83-95, (2001).
Description:
Simulations using a one-dimensional, analytical, vadose zone, solute transport screening code (VFLUX) are conducted to assess the effect of water saturation, NAPL saturation, degradation half-life, and first-type, time-dependent and second-type, zero-gradient boundary conditions at the unsaturated zone - capillary fringe interface on model output. At high initial soil concentrations, model output is significantly affected by input parameters and lower boundary conditions yet still results in consistent decision making to initiate or continue venting application. At low soil concentrations, however, typical of what is observed after prolonged venting application, differences in model input and selection of lower boundary conditions result in inconsistent decision making on whether to continue or cease venting application. Specifically, under conditions of low water saturation, use of the first-type, time-dependent lower boundary condition indicates that the primary direction of mass flux is from the capillary fringe to unsaturated soils suggesting little benefit from continued venting application. Use of the zero-gradient low boundary condition however indicates continued mass flux from unsaturated soils to the capillary fringe and suggesting a continued need for venting application. In this situation, sensitivity analysis of input parameters, assessment of boundary conditions, and consideration of overall objectives in unsaturated zone modeling become critical in regulatory decision making.