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i <br /> Julian Munoz <br /> WE'!SS ASS0CL4 TtS <br /> March 30, 1438 <br /> o The average annual rainfall is Stockton is lit.! inches per year, and <br /> thn tank piL excavation will be capped with an impermeable cover. <br /> Therefore, the potential for leaching of hydrocarbons to ground water <br /> is low. <br /> o No deep vertical conduits such as faults, unprotected wells or utility <br /> trenches have been identified near the site. <br /> o The soil beneath the slab is low-permeability clay, which should tend <br /> to sorb the hydrocarbons and inhibit their migration. <br /> o No hydrocarbons have been detected i.n three existing ground water <br /> monitoring. wells installed adjacent to the excavation. <br /> o Approximately three feet of unsaturated soil occurs between the bottom <br /> of the slab and the top of the saturated zone at about 18 ft below <br /> grade. Removal of the slab to access this soil would be very cost <br /> and is not justified by *he quantity of hydrocarbon that would be <br /> removed with the soil. <br /> r <br /> PROPOSAL FOR FINAL EXCAVAHOR CLOSURE <br /> For final closure of the excavation we propose to: <br /> 1) To comply with the request of Dave Carls of the SJL11D, we propose <br />� . installing an additional ground water monitoring well between wells <br /> WW-2 and M14-3, near the northwest corner of the excavation (Figure <br /> 1), This well will be screened in the upper few feet of saturated <br /> soil. and into the unsaturated zone. <br /> _ 2) Develop the new well. and collect ground water samples from it ana <br /> from the existing wells for analysis for TPH by GC/FID --and or <br /> benzene, toluene and xylenes (BTX) by gas chromatography with photo <br /> ionization detection (GC/PID). <br />