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7 <br /> Because the drawdown in well RW-1 exceeded 20% of the saturated screen interval the <br /> correction of Jacob (1946) was applied The corrected drawdown is calculated as follows <br /> S, = s - s1/2D , where <br /> s = observed drawdown <br /> D = saturated screen thickness <br /> a <br /> Only the corrected data for RW-1 are shown on Figure 3 <br /> In tests where the specific capacity of the well (gallons per foot of drawdown) is low in relation <br /> to the casing size a significant period of the test can be expected to be affected by well bore <br /> storage The time when the casing storage effects become negligible (tr) was calculated using <br /> the methods of Shafer (1978) and Driscoll (1988) The Shafer method yielded a t, of 53 <br /> minutes Using a modified version of the Papadopulas-Cooper Method (Driscoll, 1988) a t, of <br /> 21 minutes was calculated however, this approach assumes 100% well efficiency These <br /> estimates indicate data from the initial 20-50 minutes of the test cannot be interpreted in terms <br /> of radial flow within the aquifer During this portion of the test much of the pumped water was <br /> derived from the well casing Only after the water level has been lowered significantly does the <br /> aquifer begin producing Various factors contribute to the occurrence of this effect, including <br /> permeability of the formation, the degree of well development and the relationship of casing <br /> diameter, pump column diameter and pumping rate (Driscoll, 1988) <br /> Moderate hydraulic conductivity such as observed at the subject site results in the need for larger <br /> drawdown to bring water into the well. More importantly, the low pumping rate in a relatively <br /> large diameter well (6 inch) does not induce a significant volume of water flow from the aquifer <br /> during early pumping times <br /> Casing storage effects may also be observed in monitoring wells that are close to the pumping <br /> well Casing storage can be significant for monitoring wells if r/ra, is Iess than 300, where <br /> r = distance from pumping well, and <br /> ra, = radius of well casing (Walton, 1988). <br /> The two observation wells that are within 75 feet (r/r,, = 300) of RW-1 (MW-1, PZ-1) both <br /> show a very brief lower slope which steepens to a straight line trend extending beyond <br /> approximately 1-20 minutes on the semilog plots. Monitoring well MW-3 is sigruficantly further <br /> away from RW-1 (r/r, = 320) and does not show this apparent early time response like MW-1 <br /> and PZ-1 In any event, these affects do not affect the validity of later time data. <br /> As the proportion of production derived from casing storage declines after about 15-20 minutes <br /> the semilog straight line segment representative of formation flow appears Transmissivity (T) <br /> and storage coefficient (S,,) values were calculated from this data using the drawdown versus <br /> time Methods of Cooper and Jacob (1946) and Neuman (1972) The plots are shown on Figures <br />