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collected between 74 and 127 feet bgs in borings B-1/MW-9 and CPT-1. Benzene (13 µg/kg) <br /> was detected in the soil sample collected from 138 feet bgs at boring CPT-1. The vertical extent <br /> of petroleum hydrocarbon impact to soil is not completely characterized in the vicinity of the <br /> former UST. <br /> Petroleum hydrocarbons or fuel oxygenates were not detected in any of the soil samples collected <br /> above 93 feet bgs at any of the CPT borings advanced outside of the former UST complex area. GQ_r°o 4�w� <br /> This observation is a function of the sampling intervals in the borings and the analytical data <br /> available, and does not indicate that no impact exists above 93 feet bgs. TPHG and benzene <br /> were detected in soil samples collected between 93 and 113 feet bgs at boring CPT-10, at 93 feet f1 <br /> bgs in boring CPT-11, and at 95 feet bgs in boring CPT-8. TPHG (1.2 mg/kg) was detected in <br /> the soil sample collected from 122 feet bgs at boring CPT-2. The lateral extent of petroleum <br /> hydrocarbon impact to soil appears to have been adequately assessed. TPHG, benzene, TBA, <br /> and 1,2-DCA concentrations in soil are included on cross-sections A-A' and B-B' <br /> (Figures 3 and 4, respectively). <br /> It appears that vertical migration of petroleum hydrocarbons in soil happened at a time when <br /> groundwater elevations were between 65 and 95 feet bgs. Significant hydrocarbon <br /> concentrations were detected in borings near the former UST to at least 66 feet bgs. During the <br /> period the Apache UST was in use, groundwater in the site vicinity was known to have been as <br /> low at 105 feet bgs. These deep water depths likely allowed significant vertical migration of <br /> hydrocarbons. A subsequent rise in water levels has submerged the impacted soil. <br /> Former Sunland Gasoline Facility <br /> Significant levels of impact have been detected beneath the former USTs to at least 50 feet bgs, <br /> and this impacted soil has been submerged by rising groundwater levels. Given the high <br /> concentrations identified at the Sunland site, the presence of a transmissive (i.e. sandy)graturn at <br /> approximately 50 feet bgs beneath bQtlLthe ormer Sunland and former Apache USTs, and the <br /> predominant southerly flow in the upper portion of the water-bearing zone, it appears that <br /> hydrocarbon impact emanating from the former Sunland site might have co-mingled with the <br /> hydrocarbon impact from the former Apache UST. <br /> Petroleum hydrocarbons were detected in soil samples collected between 15 and 80 feet bgs in <br /> boring B-1, and between 5 and 30 feet bgs in boring B-2. The highest concentration of TPHG <br /> (15,000 mg/Kg) was detected in the soil sample collected from boring B-1 at 15 feet bgs, the <br /> highest concentration of benzene (32 mg/Kg) was detected in the soil sample collected from <br /> boring B-1 at 40 feet bgs, and the highest concentration of MTBE (51 mg/Kg) was detected in <br /> the soil sample collected from boring B-1 at 25 feet bgs. Soil and analytical results from the <br /> investigation conducted at the former Sunland Gasoline Station are included in Appendix C. <br /> Based on the information provided in the March 2000 WHF report, the highest petroleum <br /> hydrocarbon concentrations appear to be present in the vicinity of the former UST complex. <br /> p:\p,pache Plasdcs\Reports\Apache SCM.doc Page 8 Stratus <br />