Vapor flow to horizontal wells in unsaturated zones
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abstract
We have solved the linearized vaporflow equation in a transient, three dimensional form for a horizontalwell sink in an unsaturated zone. This is done by solving the vapor flow to a point sink first, then superposing the pointsink solution along a finite length of the horizontalwell axis to obtain the solution of flow to a horizontalwell sink. Vaporpressure distributions near a horizontal well are provided for both covered and uncovered ground surface cases. A computer program VF3D (available from our website) is used to calculate the vapor pressure and to generate the type curves of vaporpumping tests. The derived solution is used to calculate the specific vapor flux and the total vapormass flux across the uncovered ground surface. The type curves at early time for a covered surface case are influenced by the locations of the monitoring wells and vertical anisotropy of the unsaturated zone. These type curves converge to the verticalwell Theis curve at late time. The type curves for an uncovered surface case are significantly different from the Theis curve during the entire pumping time, and are similar to the type curves of leaky aquifers. The steadystate contour maps of mass fluxes across the uncovered surfaces are plotted. The transient total mass flux rate converges exponentially to the horizontalwell pumping rate, independent of the horizontalwell elevation. The derived analytical and numerical solutions are useful for assessing the performance of soilvapor extraction, bioventing, enhanced bioremediation, air sparging, and for interpreting vaporpumping tests.
