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i 4.3 Extent of Petroleum Hydrocarbon Impact to Soil Former Apache Plastics Facility Soil beneath the former Apache Plastics facility property is impacted with GRO, BTEX, TBA, and 1,2-DCA. Soil analytical results for samples collected during historical site assessment activities are presented in Figure 8 and Appendix G. The highest concentrations of petroleum hydrocarbons in soil are generally observed near the northern portion of the property, in the vicinity of the former UST and fuel dispensing area. Prior to completion of soil vapor extraction (SVE) (further discussed in section 5.1), GRO and benzene concentrations in the unsaturated zone were reported at maximum concentrations of 2,800 milligrams per kilogram (mg/Kg) and 10 mg/Kg, respectively (29 feet bgs, B-1/MW-1), 7,400 mg/Kg and 80 mg/Kg, respectively (21 feet bgs, boring VEW-1), and 11,000 mg/Kg and 130 mg/Kg, respectively (boring MP-1, 36 feet bgs). Relatively low concentrations of petroleum hydrocarbons were reported in soil samples collected from recently completed well boring MW-13 between approximately 11 and 31 feet bgs, with increased hydrocarbon concentrations observed at approximately 41 feet bgs, near the historical highest groundwater level beneath the site. Based on this observation, and the position of well MW-13 relative to the former UST complex and the area where SVE remediation was completed, SVE appears to have been effective in significantly reducing petroleum hydrocarbon concentrations in soil within the unsaturated zone. Based on the findings of post remediation site assessment activities completed since 1997, concentrations of residual petroleum hydrocarbons remain in the vicinity of the UST area between approximately 40 and 100 feet bgs. For samples collected during the recent site investigation, GRO was reported at a concentration of 4,900 mg/Kg for a sample collected from boring MW-13 at 41.5 feet bgs. Concentrations of GRO ranged from 1,300 mg/Kg to 1,900 mg/Kg for soil samples collected between 75.5 and 96.5 feet bgs at boring MW-13. Benzene was also reported in soil samples collected between 75.5 and 96.5 feet bgs at boring MW-13 (13 mg/Kg to 20 mg/Kg). GRO (250 mg/Kg) and benzene (1.7 mg/Kg) were also detected in a sample collected from boring MW-14 at 81 feet bgs. Based on the results of soil samples collected from boring CPT-1, petroleum hydrocarbon impact to soil extends to at least 138 feet bgs near the former UST area. Residual petroleum hydrocarbons in soil appear to decrease significantly below the laterally continuous lower water bearing zone strata. MTBE, TBA, 1,2-DCA, and additional fuel additives have not been detected in any soil samples collected beneath the site. Former Sunland Gasoline/Stockton City Cab Company Facility Soil beneath the former Sunland Gasoline/Stockton City Cab Company property is impacted with GRO, BTEX, MTBE, TBA, ethanol, 1,2-DCA, and EDB. Soil analytical results for samples collected during historical site assessment activities are presented in Figure 9 and Appendix H. The highest concentrations of residual petroleum hydrocarbons were generally t{.`ppache Plastics\Rcportslapache-scm-assessment report2006.doc Page 11 STP.IITUS