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Working To Restore Nature <br /> 5.2.4 Data Evaluation <br /> The data from the constant rate test were used to estimate formation transmissivity by two <br /> ' methods 1) the Jacob time-drawdown method and 2) the relationship between specific capacity <br /> and transmissivity. <br /> Jacob Method: <br /> The drawdown in the pumping well was plotted against the log of time in order to estimate <br /> transmissivity according to the formula. <br /> T = 264Q les <br /> where- <br /> T = transmissivity in gpd/ft <br /> Q = pumping rate in gpm <br /> es = change in drawdown with each order of magnitude change in time (one log cycle) <br /> The first stabilized or straight line segment of the plotted curve was evaluated and entered into <br /> ' the above equation. The stabilized portion of the curve was selected based on a calculation to <br /> determine the critical time "t," at which the casing storage component of drawdown is no longer <br /> ' significant. During the initial portion of a test, much of the pumped water is derived from the <br /> well casing Only after the water level has been lowered significantly does an aquifer begin <br /> producing. As the proportion of production derived from casing storage declines, the semi-log <br /> straight line segment representative of the formation can be expected to appear. The formula <br /> for this calculation was determined by Schafer (1978) and takes this form: <br /> 0 .6 (d'-dp) <br /> tom= QIS <br /> where: <br /> to = time in minutes when casing storage becomes negligible <br /> ' do = inside diameter of well casing in inches <br /> dF = outside diameter of pump discharge pipe in inches <br /> Q/s = specific capacity in gpm/ft at time � <br /> 1500 SMEPOMWAP-0794 DRF 8 <br /> 1 <br />