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ntlahl & <br />The Theis nonequili6rium equation far the <br />drawdown distribution about a point sink <br />(well) is: <br />Drawdown = (114.6 Q)W(u) <br />T <br />oe -LL <br />Where W(u) _~ U C~U <br />u <br />U = (1.87) (r)'-'(S) <br />(T) (t) <br />8 = pumping rate (gpm) <br />T = aquifer transmissivity (gpd/ft) = Kd <br />S = aquifer storage coefficient (a decimal) <br />r = radial distance between point sink and <br />observation point <ft) <br />t = time since pumping began (days) <br />d = thickness of aquifer (ft) <br />In the pump test of Well # 18401, all the <br />values arEa given except the aquifer transmis- <br />sivity T, and the aquifer storage coefficient <br />S. By acijustinq S and T to match the pump <br />test results} the aquifer parameters can 6e <br />estimated, These values are then used to <br />evaluate the ground water impact due to the <br />proposed mining operation. <br />The storage coefficient of a glacial till <br />deposit u<~ually is about 20 to 25'/.. The <br />transmissivity can vary greatly from .000001 <br />to 10 gpd/ft~. (See "Ground Water" 6y Freeze <br />and Cherry, page 29). Using a value of .23 <br />for 5 and adjusting T to find the correct <br />drawdown, yields the following results: <br />Q = 10 gpm, r = 1.5 ft, t = 1 = .04167 days, d = 15 ft) <br />24 <br />Drawdown for various aquifer coefficients (ft) <br />"f = 150 T = inn T = 50 T = 40 <br />S - 0.20 I1.9 13.9 15.9 15.9 <br />S = 0.22 11.3 13.0 14.5 14.3 <br />5 = 0.25 10.4 11.9 12.7 1c2.2 <br />The most :likely value for S is .22 and T is <br />50. <br />6 <br />& Environmental <br />