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N <br /> r <br /> ;y GROUNDWATER ANo WELL HYDRAULICS 155 <br /> XTABLE 4A Relation of Well Loss Coefficient <br /> to;Nell Condition(after Walton70) I <br /> Well Loss Coefficient <br /> C.mini/ma Well Condition <br /> 0.5 Properly designed and developed <br /> 0.5 to 1.0 Mild deterioration or clogging <br /> 1.0 to 4.0 Severe deterioration or clogging <br /> _r >4.0 Difficult to restore well to <br /> original capacity <br /> G <br /> bilizes.34•40.59 The discharge is then increased through a successive <br /> series of steps as shown by the time-drawdown data in Fig. 4.31x. <br /> Incremental drawdowns as for each step are determined from ap- <br /> proximately equal time intervals.The individual drawdown curves <br /> should be extrapolated with a slope proportional to the discharge i <br /> Yd. in order to measure the incremental drawdowns. y , <br /> From Eq.4.87 and letting n = 2, <br /> - =B +CQ (4.68) L <br /> Q ' <br /> Therefore,by plotting sw/Q versus CQ(see Fig.4.31b) and fitting a <br /> straight line through the points, the well loss coefficient C is given <br /> by the slope of the line and the formation loss coefficient B by the <br /> _ intercept <br /> :.! <br /> tt RorabaughS3 presented e. modification of this graphic analysis to <br /> determine n in cases where it deviates significantly from 2. <br /> ,e <br /> ss e; <br /> 4r Specific Capacity <br /> If discharge is divided by drawdown in a pumping well,the specific E'' <br /> 3£ a <br /> y capacity of the well is obtained.This is a measure of the produc- <br /> tivity of a well; clearly, the larger the specific capacity, the better <br /> :e Starting from the approximate nonequilibrium equation <br /> - the wall. S g <br /> 'n (Eq. 4.41) and including the well loss, <br /> 1d <br /> C - _2.30Q 2.25Tt i' <br /> C S,_ 4n C log re«S +CQ^ (4.89) f °: ; <br /> 1 <br /> so that the specific capacity = f <br /> en <br /> lyQ _ 1 (4.70) <br /> s (2.30/4nT)!43g(2.25T1/r =S) +CQ"-' <br /> a_ m <br />