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1 � � SIERRA Clint Rogers Page 2 October 30, 1991 SES Project #1-146-01 (BTX) TPPH(G) and BTX were not detected in the soil samples analyzed from the boring The groundwater sample was also analyzed for TPPH(G) and BTX Nine hundred and ninety parts per billion(990 ppb)TPPH(G)were detected in the ground water sample from the well Thirty-two ppb benzene was also detected in the ground water sample from the well A quarterly ground water monitoring program was initiated at the site in July 1990 In January and March 1990, SES personnel visited the site to sample the well There was insufficient water in the monitoring well for sampling SES drilled and installed four monitoring wells, MW-2 through MW-5, at the site in July 1990' Hydrocarbons were not detected in soil samples analyzed from the borings or in ground le, water samples collected from the four wells The analytic results for soil samples are shown in Table 1 (Appendix B) Seven ppb of 1,1-dichloroethane was reported in the groundwater sample from well MW-5,located near the waste oil tank The analytic results for water samples are shown in Tables 2 and 3 (Appendix B) TOPOGRAPHIC AND GEOLOGIC SETTING The site is located on level ground Surface water drainage is to the southeast The site is located in the Eastern San Joaquin Basin(SJB) Hydrogeologic Study Area The SJB has experienced severe overdraft for the last several years Water levels have declined and poor quality ground water from the Delta has moved east toward the City of Stockton' Water quality in the Stockton area has been affected and wells have been abandoned in the western part of the area New wells have been drilled in the eastern part of the city and ground water has been 2 Sierra Environmental Services, 1990 Subsurface investigation Report prepared for Chevron, October 8 1990, �} 8 pages and 5 appendices 3 Ground Water Basins in California, 1980 California Department of Water Resources Bulletin 118-80, 72 pp