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Canepa's Car Wash <br /> 6230 Pacific Avenue, Stockton, California January 31, 1995 <br /> Groundwater Pump Test Page. 5 <br /> All observation wells showed effects of recharge water reaching the aquifer at <br /> approximately 50 minutes into the recovery period (Appendix A) The return to the <br /> static water level requires a recovery period considerably longer than the pumping <br /> period, except in the case where recharge to the aquifer occurs during the pumping <br /> and recovery periods The result of the recharge is to bring about full recovery of the <br /> water level to the original static level during a relatively short recovery period This is <br />' shown on the data plots when the straight line does not intersect the zero drawdown <br /> point as the ratio of O'becomes unity <br />' Due to this influence, the values of transmissibility are not valid for the recovery <br /> portion of the test <br />' 4.3 Distance-Drawdown <br /> A Distance-Drawdown plot was constructed from the observation wen data at 700 <br />' minutes (Appendix D) Calculated T was the same as for N W-1 during the <br /> drawdown test, 1,490 gpd/ft The Storage Coefficient from the distance-drawdown <br /> plot calculated at 0 0111 Projection of the straight line to zero drawdown gives an <br /> Ro value (distance from the pumping well where there is no drawdown) of 140 feet <br /> This is the radius of the cone of depression At the other end of the straight line plot, <br /> where it intersects the radius of the pumping well (in feet) is the theoretical drawdown <br />' of 4 05 feet The actual drawdown of 7 74 feet is the result of partial penetration of <br /> the aquifer by the well screen and encountering impermeable boundaries within the <br /> volume of the cone of depression <br /> From a Distance-Drawdown graph, T=528 Q/ds and S =0 3 Tt/ro2 <br />' where <br /> Q=pumping rate, in gpm <br /> ds= slope of the distance-drawdown graph expressed as the change in <br />' drawdown, in feet, between any two values of distance on the log <br /> scale whose ratio is 10 <br /> t=time since pump started, in days <br /> ro=intercept at zero drawdown of extended straight-line, in feet <br /> 4.4 Permeability <br /> Permeability for this water table aquifer was calculated using the formula <br /> P= 1055 Q log rz "r, = 126 gpd/sq ft <br /> (hz — <br />