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observed in the southwest portion of this property, near the former UST complex and boring B-1.
<br /> Maximum concentrations of GRO (15,000 mg/Kg), benzene (32 mg/Kg), toluene (650 mg/Kg),
<br /> ethylbenzene (340 mg/Kg), xylenes (1,700 mg/Kg), MTBE (51 mg/Kg), ethanol (33 mg/Kg),
<br /> and TBA (0.62 mg/Kg) were reported within boring B-1 samples. Impacted soil samples within
<br /> the unsaturated zone were also reported for samples collected from borings B-2, B-5, MW-1, and
<br /> MW-3. Given the position of these boreholes at the subject property, impacted soil appears to
<br /> also be present in the general vicinity of the former fuel dispenser islands.
<br /> GRO (4.3 mg/Kg), BTEX (benzene at 0.231 mg/Kg), and MTBE (0.172 mg/Kg) were reported
<br /> for a sample collected from boring MW-4 at 100 feet bgs. Based on this observation, petroleum
<br /> hydrocarbon impact to soil extends to at least 100 feet bgs beneath this property.
<br /> 1,2-DCA impact to soil has been reported in soil samples collected from borings MW-1, MW-2,
<br /> MW-3, MW-5, MW-6, MW-8, MW-9, B-4, and B-5, at concentrations ranging from
<br /> 0.007 mg/Kg to 0.147 mg/Kg. 1,2-DCA was only reported in one soil sample collected above 40
<br /> feet bgs (0.011 mg/Kg, boring B-5, 30 feet bgs). 1,2-DCA impact extends to at least 89.5 feet
<br /> bgs in the vicinity of well boring MW-6.
<br /> 4.4 Extent of Petroleum Hydrocarbon Impact to Groundwater
<br /> Groundwater beneath the Former Apache Plastics Facility property, and the Former Sunland
<br /> Gasoline/Stockton City Cab Company Facility property, is impacted. A network of monitoring
<br /> wells has been installed at both sites to evaluate petroleum hydrocarbon and fuel additive
<br /> concentrations at various depths within the subsurface. Figures 10 through 21 illustrate iso-
<br /> concentration contours for GRO, benzene, MTBE, and 1,2-DCA for the shallow, mid-depth, and
<br /> deep groundwater monitoring wells, using data collected from both sites during the second
<br /> quarter 2006. The following subsections discuss the extent of impact to groundwater in the site
<br /> vicinity.
<br /> Former Apache Plastics Facility
<br /> The highest concentrations of GRO and BTEX remain-in groundwater in the general vicinity of
<br /> the former UST and fuel dispensing area. GRO and benzene concentrations in shallow
<br /> groundwater were reported at 12,000 micrograms per liter (µglL) and 1,500 µg/L, respectively
<br /> (VEW-1), and 99,000 µg/L and 1,300 µg/L, respectively (VEW-2) for samples collected in April
<br /> 2006. Relatively high concentrations of GRO and benzene also impact deeply screened wells
<br /> MW-9 (74,000 µg/L and 11,000 µg/L, respectively), MW-13 (95,000 µg/L and 11,000 pg/L,
<br /> respectively), and MW-14 (16,000 gg/L and 130 .µg/L, respectively), situated at variable depths
<br /> between approximately 94 and 115 feet bgs near the former USTs.
<br /> Petroleum hydrocarbon impact to shallow groundwater east (generally downgradient) of the
<br /> former Apache Plastics facility building appears limited. Concentrations of CTO and BTEX
<br /> compounds in samples collected from wells MW-2, MW-4, MW-6, and MW-15, have
<br /> predominately been reported below laboratory detection limits; however low concentrations of
<br /> hydrocarbons have been periodically detected at each well location.
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