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Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA, Page 43 <br /> i <br /> traveled from that time until the present to evaluate the mean hydraulic conductivity of <br /> lk'v n. the formations through which it has migrated. <br /> Recalling that: <br /> r: v=i K/n (Equation 2) <br /> or, by rearrangement, <br /> K= n v/i (Equation 3) <br /> -� where: <br /> v=the groundwater velocity <br /> i =the groundwater gradient <br /> and <br /> n=the effective porosity of the permeated media <br /> l' Then, for the following data set, which is based on the field observations made at the <br /> 7500 West Eleventh Street site and the assumptions stated above, <br /> Distance= 735 ft <br /> Time of Migration= 9.5 years (i.e., from October 1992 through March 2002) <br /> Porosity= 0.3 <br /> _l Groundwater Gradient = 0.003 ft./ft. (as measured on April 11, 2002 between Wells <br /> MW-3 and MW-11) <br /> .J <br /> And, after performing the necessary unit conversion calculations, Equation 3 yields: <br /> K= 1.5 x 10-2 cm/sec. <br /> The computed value of 1.5 x 10-2 cm/sec for the hydraulic conductivity is a very <br /> rj satisfactory result because it is consistent with the typical hydraulic conductivity of the <br /> loose sands in the permeable strata beneath the subsurface of the site. It also compares <br /> very favorably with the hydraulic conductivity of 2.0 x 10-2 cm/sec derived from pump <br /> tests previously conducted by SJC at 152 East Eleventh Street in similar sandy aquifers at <br /> shallow depth in the same alluvial fan (The San Joaquin Company Inc. 1994). The result <br /> also validates the interpretation of the lateral extent of the primary plume of affected <br /> groundwater emanating from the 7500 West Eleventh Street site that is presented on <br /> Figure 13. <br /> �i SJC <br /> .J <br />