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3.3 Hydrogeologic Setting 19 Groundwater in the new boreholes was initially encountered at depths ranging from 55 ! to 57 feet BGS within silty and clayey sand intervals In response to the confining or semi-confining characteristics of the overlying clayey materials, groundwater in the wells ' eventually stabilized about 3 to 5 feet higher than the groundwater table As shown on Figure 8, groundwater elevations in the wells ranged from —34 69 to ' —35 40 feet, relative to MSL Groundwater flow is northeasterly at a gradient of about 2 5 x 10-3 feet per feet (ft/ft) ACG performed a 24-hour well pumping test at this facility on June 11 and 12, 1991 ' Details of the pumping test are included in the December 19, 1991, Problem Assessment Report Well MW-1 was pumped at an average discharge flow rate of 6 7 gallons per minute For the last 4 hours of the test, drawdown in MW-1 ranged from 10 36 to 11 64 feet Wells MW-2, MW-3, MW-4, MW-6, and MW-8 were observed for drawdown to evaluate the zone of influence of the pumping well All five observation wells were affected by the pumping From the pump test data, ACG estimated the average aquifer transmissivity to be ' 6,248 gallons per day per foot of aquifer thickness (837 2 square feet per day), and the average storage coefficient to be 0 027 Lateral hydraulic conductivity of the aquifer is derived by dividing transmissivity by the saturated thickness of the aquifer Using a ' saturated thickness of 50 feet, hydraulic conductivity was calculated to be 16 74 feet per day (ft/d) ' Average linear flow velocity of the groundwater system is estimated by multiplying lateral hydraulic conductivity and gradient values, and dividing this product by effective ' porosity Using an approximate effective porosity value of 18 percent (0 18), which is not uncommon for clayey sands, the groundwater flow velocity was calculated to be 0 23 ft/d I 04/94/121382/125997/STOCKREP REP/1