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December 16, 1992 Working To Restore Nature <br /> Unocal Service Station No 6981, Stockton, California <br /> Assessment of Soil <br /> Soil-Vapor Survey <br /> Following the tank replacement and excavation of soil, RESNA performed a soil-vapor <br /> survey at the site in December 1988 Results of the survey indicated that low levels of <br /> gasoline hydrocarbons were present in a soil vapor probe hole near the southwest corner <br /> of the site, however, the test provided no conclusive data on hydrocarbons below 13 feet <br /> below grade (Applied GeoSystems, February 19, 1991) <br /> 1 <br /> Soil Borings <br /> To evaluate and delineate residual hydrocarbons in soil and dissolved hydrocarbons in <br /> R <br /> ground-water, fourteen soil borings were drilled onsite and five soil borings were drilled <br /> offsite (Applied GeoSystems, February 19, 1991, and RESNA,June 30, 1992) Plate 2 shows <br /> the locations of the soil borings <br /> 1 <br /> A geologist from RESNA collected soil samples from each boring for laboratory analysis of <br /> hydrocarbons and other selected compounds and to characterize the geology beneath the <br /> I site Sediments were logged using the Unified Soil Classification Svstem (Appendix B) The <br /> geologist also analyzed the soil samples with a field photoionization detector to characterize <br /> the relative levels of hydrocarbons in the samples The sediments encountered and the <br /> photoionization detector readings are presented on the Logs of Borings (Appendix B) The <br /> I details of the borings such as boring depth, diameter of the boring, and drilling method are <br /> shown on Table 1 <br /> I <br /> 38032 10 J <br />