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APPENDIX B <br /> HANTUSH FLOW MODEL <br /> (continued) <br /> where Ei(u) = exponential-integral function (the well function W(u) <br /> u = FS <br /> 4Tt <br /> r = radius from extraction well <br /> T — air transmissivity of the extraction zone <br /> t = time <br /> S = Storativity <br /> Q = pumping rate <br /> (l� _ h) = pressure drawdown <br /> B = (Tb,/K,,r <br /> by = thickness of confining layer through which leakage occurs <br /> K, = vertical conductivity of confining layer through which leakage <br /> occurs <br /> Equation (2) is called the Hantush Solution of the radial diffusion equation for leaky <br /> aquifers with no storage in confi nng zone The exponential-integral equation Ei(u) is a <br /> dimensionless drawdown that is plotted against the dimensionless time or its reciprocal (u <br /> or 1/u) on the Hantush-type curve, for different values of f/B <br /> To analyze the pressure drawdown data from a vapor extraction test, the analyst converts <br /> the pressure drawdown data (inches of water) to feet of air The conversion factor is <br /> calculated to 833 3 inches of air per inch of water (the ratio of the density of water to the <br /> density of air). <br /> The analyst then plots the pressure drawdown (feet of air) versus the elapsed recovery time <br /> (t) on a log-log scale. A curve is fitted to the actual test data plot, and the transmissivity <br /> (T), the storativrty (S), and the r/B term related to the confining zone are obtained from <br /> a match point. <br /> The soil permeability is calculated from the estimated soil transmissivity value. The <br /> calculation is as follows <br /> k = Tu/Bdg <br /> where k = soil permeability <br /> T = soil transmussivity <br /> U = air viscosity (0.18 centipoise) <br /> b — vadose zone thickness <br /> D = air density (0.075 lb/ft3 or 0 0012 g/cm3) <br /> 0 9 gravitational acceleration (32.2 ft/secs or 981 cm/sect) <br />