In situ soil remediation using vapor extraction wells, development and testing of a three-dimensional finite-difference model

Soil vapor extraction technology is becoming increasingly popular in soil remediation in removing volatile and semivolatile organic compounds from the vadose zone. The rate and extent of removal of volatile organic compounds from the vadose zone by active or passive vapor extraction systems are known to be affected by a number of factors, including soil permeability, soil moisture content, applied suction, air flow rate, temperature, vapor pressure, and external boundary conditions. Some techniques used to describe the dynamics of gas flow are based on simplifying assumptions which limit their application in "real world" situations. This paper describes the development and testing of a three-dimensional gas flow model "GAS3D" for the design of soil venting systems. The model takes into account the effect of partial penetration and partial screening of vapor extraction wells as well as the nonhomogeneity and anisotropy of the soil. The simulated pressure around a vapor extraction well by the developed GAS3D model was verified and validated by comparing the results of the finite-difference solution to the actual field measurements and the results of an analytical solution under homogeneous and isotropic conditions. The model was used in a case study to demonstrate the utility of the developed model under heterogeneous and anisotropic conditions for designing a vapor extraction system.