Laserfiche WebLink
modified solution to the instantaneous slug test accounts for the <br />• opposing theories of an aquifer's response to slug and pumping <br />stresses. The slug test assumes that there is no aquifer discharge <br />until after the well is "slugged". The standard pumping test <br />(Theis assumptions) solutions assume that aquifer discharge only <br />occurs during the pumping phase of a test and there is no casing <br />storage. The modified slug type curves account for the two <br />opposing scenarios, thereby allowing the pumping. test recovery data <br />to be analyzed in a similar manner to an instantaneous slug test. <br />The solution is arrived at by superimposing the data curve on top <br />of the modified type curves. Appendix F contains the modified type <br />curves in tabular and graphical form. <br />McWhorter (1982) also provides an alternate method for analyzing <br />recovery data. In those cases where the volume of water pumped <br />from the aquifer is 70 percent or more of the total volume of water <br />pumped, the standard recovery theory can be modified to account for <br />the effects of continued aquifer discharge or afterflow. The <br />• afterflow can be determined using the following relationship: <br />Q1 = rc2(So S1)/(tl-to) (2) <br />where: <br />Q1 = Aquifer discharge at time increment tl <br />to = Time pumping ceases <br />tl = Time increment since pumping ceased <br />So = Drawdown at time to <br />S1 = Drawdown at time increment tl <br />rc =Radius of casing over which the water level <br />fluctuates <br />Equation 2 can be generalized to become: <br />ti - ti_1 <br /> <br />81 <br />