Modeling dense non-aqueous phase liquid transport through saturated porous media

Abstract

DNAPLs (dense non-aqueous phase liquids), such as certain chlorinated hy drocarbons, are some of the prevalent substances contaminating the groundwater and subsurface soils. The high density and low solubility of DNAPLs make it difficult to remediate a DNAPL contaminated site. High density makes the DNAPLs migrate downward below water table and low solubility makes the remediation difficult. For effective remediation, it's important to accurately know the extent of a DNAPL at a contaminated site. This presents computational modeling of DNAPL transport through subsurface. A finite element computer code, U_DYSAC2, developed for preucting static and dynamic behavior of unsaturated soils is modified to predict the DNAPL transport through subsurface. The air-phase and related constitutive relationships governing multiphase flow in U_DYSAC2 are replaced with DNAPL and corresponding relationships. A parametric study is conducted using the modified U_DYSAC2 to see the influence of DNAPL density and viscosity and the groundwater flow on the subsurface transport of DNAPL and qualitatively reasonable results are obtained. Quantitative validation of U_DYSAC2 is conducted by comparing the predictions against a centrifuge model test and a laboratory test results. The centrifuge test involved low density high viscosity DNAPL transport and the laboratory test was done on a heterogrneous stratified soil stratum. Reasonable comparisons between the U_DYSAC2 predictions and the tests result are obtained.