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76 GROUNDWATER PUMPING TESTS 1.0 095-) 0.8 <J 0.6 1.1- fi 0 -0 0.4 .. 0 L 0 0.2 0.0 10 100 1000 4 Step Drawdown Test Analysis Distance (F t) Figure 3.9. Distance-drawdown graph for Example Problem 3.8. One of the components of drawdown in a production well is well loss due to the turbulent flow of water through the well face and inside the casing to the pump bowls. Well loss is estimated using data collected during a step drawdown test which consists of operating the pump in the production . well during three successive periods usually 1 hour in dura- tion at constant fractions of full capacity. Water levels in the production well are measured at frequent intervals as is the discharge rate. infiltration rate is 26,460 gpdlacre based on Equation 3.44 and the lakebed induced infiltration rate per foot of head loss beneath the lakebed is 529,200 gpdlacrelft based on Equation 3.45. The lakebed induced infiltration rate per foot of head loss would be 763,033 gpdlacre/ft if the temper- ature of the surface water were 790F (see Equation 3.46). Calculations made with Equations 1.1 and 1.3 indicate that well storage impacts were negligible with r, = 0.1 ft after 1 minute of pumping and delayed gravity yield impacts were negligible with PV/PH = 1/10 before the end of the test. The distance-drawdown graph is presented in Figure 3.9. ANALYTICAL MODEL The analytical well loss model assumes well loss is proportional to the square of the production well discharge rate and the production well is stable. Well loss may be represented approximately. by the following equation (Jacob, 1946, pp. 1047-1070): Sw = CQ' (4.1) where Sw = drawdown component due to wen loss, in ft C = well loss coefficient, in sec'!ftS Q = production well discharge rate, in cfs (1 cfs = 449 gpm) The well loss coefficient may be estimated with the fol. lowing equation (Jacob, 1946, pp. 1047-1070): n