Vapor Flow to Horizontal Wells in Unsaturated Zones
- Hongbin Zhan * and
- Eungyu Park
We have solved the linearized vapor-flow equation in a transient, three dimensional form for a horizontal-well sink in an unsaturated zone. This is done by solving the vapor flow to a point sink first, then superposing the point-sink solution along a finite length of the horizontal-well axis to obtain the solution of flow to a horizontal-well sink. Vapor-pressure 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 vapor-pumping tests. The derived solution is used to calculate the specific vapor flux and the total vapor-mass 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 vertical-well 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 steady-state contour maps of mass fluxes across the uncovered surfaces are plotted. The transient total mass flux rate converges exponentially to the horizontal-well pumping rate, independent of the horizontal-well elevation. The derived analytical and numerical solutions are useful for assessing the performance of soil-vapor extraction, bioventing, enhanced bioremediation, air sparging, and for interpreting vapor-pumping tests.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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