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Remediation Report - 152 East I i th Street, Tracy, California Page 6 <br /> Hydraulic Properties of Soils <br /> To evaluate the hydraulic properties of the soils beneath the site, a series of groundwater <br /> pumping tests were conducted that used well NAV 6 as the pumped well and well NAV 3 <br /> as an observation well (Ref 11) These tests indicated that the sands that occur under the <br /> site at depths between approximately 14 and 25 ft behave as a leaky, confined aquifer but <br /> there is a significant degree of hydraulic communication between the sand aquifer and the <br /> overlying silty clays The bottom of the sand aquifer is defined by a second stratum of <br /> arealy-extensive silty clays <br /> When considered as a single equivalent hydrostratigraphic unit, the strata from the water <br /> table to a depth of 25 ft beneath the ground surface has the following hydraulic <br /> properties <br /> Transmissivity = 4,300 gpd/ft <br /> Specific Yield = 0 01 <br /> When considered separately, the following hydraulic conductivities have been estimated <br /> for the sands and silty clays found in the subsurface beneath the site <br /> Silty Clays <br /> Horizontal Hydraulic Conductivity = 40 gpd/ft2 (2 0 x 10-3 cm/sec ) <br /> Sands <br /> J <br /> Horizontal Hydraulic Conductivity = 400 gpd/ft2 (2 0 x 10-2 cm/sec } <br /> REMEDIATION PLAN <br /> During planning for corrective action to remediate the subsurface beneath the 152 East <br /> 1 I th Street site it was recognized that the highest concentration of components of <br /> gasoline were off the property under East I I th Street and that it would not be practical to <br /> attempt to remediate that area either by direct excavation of contaminated soil from <br /> beneath the street or by other active remediation technologies that would require <br /> installation of pumping wells or other remediation infrastructure under the public <br /> thoroughfare <br /> Other constraints that affected the choice of remedial technologies for this site were the <br /> adverse subsurface conditions in terms of the stability of excavations and the potential for <br /> excavation or de-watering operations to induce surface settlement over an extended area, <br /> the limitations that the shallow water table and the restrictions that the public streets on <br /> the down-gradient and co-gradient boundaries of the site impose on excavations intended <br />