Laserfiche WebLink
r = Radius of casing over which the water level fluctuates <br />c <br />This equation can be generalized to become: <br />Oi ~rcz (Si 1 - Si) <br />(ti-ti 1) <br />where: <br />0. = Aquifer discharge at any time increment and the other variables are as defined <br />i <br />above, only for time increment i. <br />Assuming the aquifer discharge becomes zero at time to then the drawdown at time = tl can <br />be determined by: <br />S1 = Oo In tl <br />471't1 t1-to <br />from which the transmissi vi ty (Tl) can be calculated using the measured drawdown (Sl) at <br />• time tl. Because the aquifer discharge at tl is not zero and significant of terf low has <br />been neglected, the transmissi vi ty at tl will be a poor approximation of the actual <br />transmi ssi vi ty. <br />The effects of of terflow on the calculated tra nsmissivity can be reduced by performing a <br />series of successive approximations on the transmissivity until the actual transmissivity <br />is obtained. The generalized form of this equation is: <br />n-1 <br />T = 1 t +~ 0 In t - t. <br />n (0 In n _ n i-1 ) <br />4T1"s o t -t ~ ~ t - t. <br />n n o n ~ <br />where: <br />n =Number of approximations <br />i = Tra nsmissivity at the nth approximation <br />n <br />t =Time at approximation n <br />n <br />0 =Discharge rate during pumping phase <br />0 <br />pi = Aquifer discharge at time increment tl <br />s = Drawdown at time n <br />n <br />• Transmissivity and hydraulic conductivity values throughout and immediately adjacent to <br />7-27 Revised 04/11/88 <br />