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Transient pumping tests are more commonly used than <br /> steady-state testa. Certain assumptions have to be made in <br /> calculating T and S from the pumping-test data, such as, <br /> the aquifer is aomogeneous, isotropic. For the purposes of <br /> aquifer testing, only the transient-state method will be <br /> used. There are two methods developed to calculate or <br /> determine the various aquifer parameters: one by Theis <br /> (1935) and the other by Cooper and Jacob (1946) , both of <br /> -- which are briefly discussed below. <br /> o Theis a jjLtjQn <br /> Theis solution is a graphical procedure for <br /> evaluating T and S. The transient flow <br /> differential equation was developed by Theis as: <br /> s = Q W(u)/(4 T) <br /> where: s = drawdown of piezometric surface <br /> Q = Pumping rate <br /> W(u) = Well function <br /> and: <br /> u = r2 S/(4Tt) <br /> where: r = The distance between the pumping and <br /> observation wells <br /> Rearranging and taking logarithms of Equations 1 <br /> and 2 yields: <br /> log (s) = log (Q/4 T) + log W(u) <br /> and,. <br /> log r2/t = log (4T/S) + log (u) <br /> From the above relationships, a logarithmic plot of <br /> s versus r2/t and a log-log plot of W(u) versus u <br /> .._ will be similar. By superimposing these two plots, <br /> a match point can be determined. Using the four <br /> coordinates of the match point and Equations 2 <br /> and 3, the transmissivity (T) and storage <br /> coefficient (S) of the aquifer can then be <br /> determined. - <br /> a Cooper-Jacob Solutign <br /> The Cooper-Jacob solution is also a graphical <br /> solution for the general transient flow equation. <br /> 9 <br />