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Supplemental Investigation Report <br /> BP Oil Site No 11193 <br /> C A M B R I A Stockton, California <br /> October 13, 2000 <br /> TBA was reported at 17,000 gg/l and 5,800 µg/l in wells MW-2 and MW-3, respectively No <br /> 1,2-DCA,EDB or ethanol were reported in the groundwater samples collected from wells MW-2 and <br /> MW-3 (see Table 3) No DIPE,ETBE,TAME, or methanol were reported well MW-3 DIPE,ETBE, <br /> TAME and methanol were reported in well MW-2 at 1 5 gg/1, 18 gg/l, 69 µg11, and 6,300 gg/l , <br /> respectively <br /> HYDROCARBON AND MTBE MASS ESTIMATES <br /> The mass of hydrocarbons and MTBE remaining in soil and groundwater beneath the site was <br /> estimated using an assumed soil bulk density of 17 kg/1, a gasoline specific gravity of 0 80,a MTBE <br /> specific gravity of 0 74, an assumed impacted surface area of 27,200 square feet (area of site), a <br /> vertical extent of 50 feet bgs, and the geometric mean of TPHg and MTBE concentrations reported <br /> in soil samples collected during this and previous investigations and in groundwater samples collected <br /> during the July 2000 monitoring event Analytical results below method reporting limits were <br /> assumed at one half this limit Based on these conservative assumptions, approximately 91 pounds <br /> . of gasoline and 55 pounds of MTBE are estimated to remain in soil beneath the site, and <br /> approximately 4 pounds of gasoline and 11 pounds of MTBE are estimated to remain in groundwater <br /> beneath the site Calculations and assumptions are summarized in Appendix G <br /> CALTRANS WELL. ASSESSMENT <br /> As previously mentioned, a Caltrans irrigation well was identified approximately 315 feet west of the <br /> site boundary The well was located on the southeast corner of the intersection between West Hammer <br /> Lane and the Interstate 5 off-ramp The well was constructed with a conductor casing from the surface <br /> to 50 feet bgs which set into the clay unit reported from 43 to 80 feet bgs, and consisted of 10 3/a-inch <br /> diameter steel casing screened from 214 to 238 feet bgs and from 254 to 350 feet bgs (see <br /> Appendix A) <br /> 10 <br />