ANALYTICAL SOLUTIONS FOR STEADY-STATE GAS-FLOW TO A SOIL VAPOR EXTRACTION WELL

Analytical solutions are developed for modeling steady state gas flow to a single vacuum extraction well in the unsaturated zone. The solutions are applicable to isotropic as well as anisotropic homogeneous subsurface media in which the ground surface is open to the atmosphere. Analytic expressions are given for the gas pressure field, and for the stream function distribution. Streamline travel times are computed using a simple numerical technique employing the analytical solutions. The pressure solution may be used to analyze in situ gas pumping tests to determine average horizontal and vertical gas permeabilities. The stream function solution and streamline travel times may be used to optimize the design of vapor extraction systems for volatile organic chemical removal from the unsaturated zone. Application of the solutions to several examples illustrates the strong effect of screen location and anisotropy on the induced gas flow field, and dimensionless type curves are given for a variety of gas well geometries.