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AQUIFER TEST CALCULATIONS <br />' Various methods of pumping test analyses, as well as the advantages and limitations of each, are <br /> discussed in published literature (Freeze and Cherry, 1979, Driscoll, 1986) Charles Theis developed <br />' an analytical solution (1935) to the radial groundwater flow equation Since this equation cannot be <br /> solved directly, Theis developed type-curves to be aligned with actual field data (plotted at the same <br />' scale) to evaluate confined aquifers <br />' Theis' solution, for a confined leaky aquifer, written in terms of drawdown(s), is <br /> _ Q r a-°dd <br /> S 4nT J u [11 <br /> where r = distance from well <br />' t = time <br /> S = storativity <br />' T = transmissivoty <br /> and where <br /> _ r 2 <br /> u 4 Tt [2] <br />' and Q is the rate of discharge The integral in equation [1] is often referred to as the well function, <br /> W(u) Using this notation, equation [1] becomes <br /> S = 4Q W(14 <br /> [3] <br /> tThe relationship between u and W(u), when plotted, is commonly called the Theis curve When data <br /> from a pumping test (drawdown vs time) are plotted on log-log paper, the shape of the function has <br />' the same form as the Theis curve The Theis curve, if plotted at the same scale, may be overlain <br /> and aligned with the test data and the transmissivity and storativity of the tested aquifer can be <br />' determined The assumptions made by Theis include <br /> • The aquifer is confined on both the top and the bottom by impermeable beds <br />' The aquifer is level and infinite in horizontal extent <br />' 2879R034 070 <br /> GROUNDWATER <br />' TECHNOLOGY, INC <br />