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y - n <br /> 1 <br /> r� <br /> ;Y GROUNDWATER AND WELL HYDRAULIGS 155 i3 <br /> � :i <br /> TABLE 4.4 Relation of Well Gose Coefficient <br /> to Well Condition(after Waltnn'0) I <br /> Well loss Coefficient <br /> C,tninz/ms 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 /> 4.0 Difficult to restore well to <br /> original capacity <br /> .t <br /> c <br /> bilizes.3*•40.59 The discharge is then increased tt.mugh a successive <br /> series of steps as shown by the time-drawdown data in Fig.4.31x. <br /> Incremental drawdowns ds for each step are determ*ngd from ap- <br /> proximately equal time intervals.The individual drawdown curves <br /> should be extrapolated with a slope proportional to the discharge F <br /> in order to measure the incremental drawdowns. <br /> From Eq.4.57 and letting n - 2, <br /> S.=fi+CQ (4.68) L <br /> Q <br /> Therefore,by plotting s./Q versus CQ(see Fig.4.316) and fitting a <br /> straight line through the points,the well loss coefficient C is given3 <br /> by the slope of the line and the formation loss coefficient 13 by the <br /> intercept Q = 0. <br /> is Rorabaugh35 presented a modification of this graph+c analysis to <br /> it. determine n in cases where it deviates significantly from 2. <br /> :e F <br /> ss <br /> 'lr Specific Capacity <br /> If discharge is divided by drawdown in a pumping well,the specific <br /> A capacity of the well is obtained.This is a measure of the produc- , '13 <br /> )y y tivity of a well:clearly. the larger the specific capacity the better <br /> ,e i..J. <br /> the well. Starting from the approximate nonequilibrium equation i i <br /> n I. <br /> (Eq.4.41) and including the well loss, <br /> id <br /> C _2.30Q log In5Tt _ '1 <br /> r. <br /> +CQ <br /> s 4aT r zS I I <br /> to a <br /> so that the specific capacity t. <br /> E ' - <br /> ,n [ <br /> l Q; 1 (4:70) <br /> y s {2.30/4aT)log(2.25T11r."S) +CQ` <br /> a- <br /> s <br /> i <br />