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Case Closure Report <br /> Former Tosco(Unocal)SS No 5421, Stockton, California <br /> July 8, 1998 <br /> • observed starting at 42 feet below grade Based on our previous research at the California <br /> Department of Water Resources for the other water well on-site (which was destroyed on <br /> January 24, 1992), this water well was probably installed prior to 1951 <br /> A water sample was collected from the second domestic well on August 21, 1992 Prior <br /> to sampling, the well was purged of four casing volumes of water by the use of a <br /> submersible pump The sample was analyzed for TPH as gasoline by EPA Method <br /> 5030/Modified 8015, and BTEX by EPA Method 8020 In addition, the sample was <br /> analyzed for EPA Method 8010 constituents The analytical results of the water sample <br /> collected from the domestic water indicated 300 ppb of TPH as gasoline, 21 ppb of <br /> xylenes, 1 3 ppb of 1,4-dichlorobenzene, and 4.8 ppb of 1,2-dichlorobenzene, with all <br /> other analyzed constituents showing non-detectable concentrations The results of the <br /> water sample analyses are presented in Appendix A Table 101) <br /> On September 24, 1992, the second abandoned water well was pressure grouted to the <br /> surface with bentonite cement grout by the use of a tremae pipe in conjunction with a <br /> grout pump On July 26 and 27, 1994, the second and final phase of the domestic well <br /> destruction was completed by fully drilling out around the existing well casing with 20 <br /> inch hollow-stem augers to the full depth of the well (approximately 78 feet deep) The <br /> borehole was then pressure grouted from the total depth drilled to the surface with 9-sack <br /> cement/sand slurry using a tremie pipe plumbed with flexible hose to a grout pump Mr <br /> Harlin Knoll of the SJCPHS was present during the well destruction operations All soil <br /> and nnsate materials generated during the well destruction operations were stored on-site <br /> pending proper disposal <br /> Phase H Soil Investigation Activities <br /> Per Unocal Corporation's procedure for potential site divestment, seven exploratory <br /> borings designated as EBI through EB7, were drilled on November 9 and 10, 1992, to <br /> document the environmental conditions at the site <br /> The seven borings were dnlled to depths of 10 to 59 feet bgs Groundwater was <br /> encountered at depths of 58 0 to 58 5 feet bgs in exploratory bonngs EB 1 through EB4 <br /> In exploratory bonngs EB5 through EB7, which were drilled to total depths of less than <br /> 58 feet bgs, groundwater was not encountered during drilling In addition, exploratory <br /> boring EB7 was drilled at an angle of 10 degrees to the vertical Soil samples were <br /> collected at a maximum spacing of 5 foot intervals, at significant changes in lithology, at <br /> obvious areas of contamination, and at or within the soil/groundwater interface, beginning <br /> at a depth of 5 feet bgs in each of the borings with the exception of EB5 and EB6, where <br /> samples were collected beginning at 4 feet bgs Drilling was stopped about 0 5 to 2 feet <br /> after intersecting the first water table Water samples were collected from borings EB1 <br /> through EB4 by the use of a clean acrylic bailer Bentonite was used to seal the bonngs <br /> within the saturated zone Grout was placed from the bentonite plug up to the surface in <br /> one continuous pour <br /> 140162 03 7 <br />