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APPENDIX B <br /> HANFUSH FLOW MODEL <br /> The theory of aquifer drawdown analysis as applied to vadose zone pressure drawdown <br /> analysis is outlined below. <br /> Hantush Flow Model <br /> Hantush (Hantush, 1956) modified thee Theis equation to allow consideration for fluid <br /> leakage from above or below the zone of testing. The Hantush equation is applied to vapor <br /> extraction testing The leaking fluid is assumed to be supplied by an infinite reservoir (the <br /> earth's atmosphere, in the case of vapor extraction testing). The rate of fluid leakage is <br /> controlled by the gradient and the vertical permeability of he material through which <br /> leakage occurs. <br /> The assumptions and conditions included in the derivation by Hantush, as applied to vapor <br /> extraction analysis, are as follows <br /> 1. The flow zone is cylindrical, homogeneous, isotropic, of uniform thickness, and of <br /> uifuute areal extent. <br /> 2 The flow rate is constant <br /> i <br /> 3. The test wells are fully penetrating the flow zone, which is semi-confined. <br /> 4. Flow to the extraction well is horizontal and unsteady <br /> 5 Fluid is released instantaneously from storage, with decline in pressure level. The <br /> initial pressure is constant and uniform <br /> 6. The diameter of the extraction well is very small so that storage in the wells is <br /> negligible <br /> 7 The confining beds have infinite areal extent, uniform vertical conductivity, and <br /> uniform thickness <br /> 8 The confining beds are overlain or underlain by an infinite constant-pressure plane <br /> source <br /> 9 Flow in the confining layer is vertical <br /> The solution is then as follows <br /> . (k-h) = Q/(4 T) Ei(u, r/B) <br />