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I <br />' Feasibility Study Report <br /> • 1140 W Hammer Lane, Stockton, CA <br /> the drilling of four additional bonngs (DB-1, DB-la, DB-2, DB-3) in the vicinity of the former USTs in <br />' June and July 1998 and one boring north of well MW5 (SB-1X) in July 2000 The locations of bonngs <br /> advanced by Ground Zero are shown on Figure 6 Analytical results are presented in Tables 6 and 7, <br />' respectively <br /> I5.0 SITE CHARACTERIZATION <br /> 5.1 Site Geology <br /> Subsurface soils beneath the site consists predominately of clays from surface grade to approximately <br />' 12 to 20 feet bgs, clayey sand to well graded sand from approximately 12120 feet to 30 feet bgs, clay <br /> and silt from approximately 30 feet to 50 feet bgs, clayey sand to well graded sand with some stilt and <br />' clay from approximately 50 feet to 70 feet bgs, and clay and silt from approximately 70 feet to 99 feet <br /> bgs, the maximum depth explored A poorly graded sand was encountered from approximately 95-99 <br /> feet bgs in boring DB-l a, the only boring at the site advanced deeper than 70 feet bgs <br />�. 52 Site Hydrology <br /> Groundwater beneath the site was encountered at approximately 49 feet bgs during the initial <br /> subsurface investigation in September 1987 The water table subsequently fell to as low as 59 feet <br /> below grade in September 1992 The water table on February 9, 2001 was approximately 30 5-32 5 <br /> feet bgs, which is near the apparent historic high of 29 5-31 5 feet bgs (May 2000) Groundwater <br /> beneath the site generally flows to the southeast with an average gradient ranging from approximately <br />' 20 to 37 feet per mile The groundwater gradient calculated from data collected on February 9, 2001 <br /> is depicted on Figure 7 <br /> 1 <br /> 5.3 Residual Hydrocarbons in Soil <br /> Analytical results of soil samples collected during subsurface investigations to date indicated gasoline <br /> hydrocarbon impacted soil was initially present in the vicinity of the former underground fuel storage <br /> tanks and fuel dispensers from approximately five feet below grade to the water table (at least 55 feet <br /> below grade) Subsequent excavation activities removed impacted soils to a depth of approximately 35 <br /> 1 to 40 feet below grade, the maximum practical depth for excavation Laboratory analyses of <br /> confirmation soil samples collected from the excavation indicated that soil contaminants were removed <br /> G IDaWGROUNDZEIKNOWLFS HANi1RLP0Rrs\rean&ihtyR.por1 doc <br />' 6 <br />