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Mr. M. Scott Mansholt—CTfWron Environmental Management Corporation'" Page 2
<br /> Pombo Property—Soil and Groundwater Investigation Work Plan July 31,2003
<br /> total petroleum hydrocarbons as diesel (TPHd), and as gasoline (TPHg), TPHc, methyl
<br /> tertiary butyl ether(MTBE), benzene, toluene, ethylbenzene, and xylenes (BTEX), and
<br /> PNAs. TPHd, TPHg, and TPHc were detected in all four samples. The maximum
<br /> detection was 18,000 milligrams per kilogram (mg/kg) TPHc at 8.5 ft bgs at GMX-2.
<br /> Benzene, toluene, and MTBE were not detected; however, ethylbenzene, xylenes, and
<br /> PNAs were detected in low concentrations in two of the four samples. Confirmation
<br /> samples taken above the water table (from 11 to 12.5 ft bgs) from seven borings outside
<br /> the area of visibly affected soils GMX-1, GMX-3, GMX-4, GMX-4, GMX-8, GMX-15,
<br /> GMX-17, and GMX-19) had no detections of BTEX, MTBE, or PNAs. Concentrations
<br /> of TPHg, TPHc, and TPHd were either non-detect or below 100 mg/kg in all samples. A
<br /> grab groundwater sample from beneath affected soil was collected in one boring (GMX-
<br /> 6) and analyzed for BTEX, MTBE, and PAHs. Two PNAs were detected, both at less
<br /> than 1 microgram per liter(µg/L). The Department of Toxic Substances Control (DTSC)
<br /> approved the findings of the 1999 screening risk evaluation, which concluded that
<br /> residual petroleum constituents in soil do not pose unacceptable health risks.
<br /> Geomatrix conducted two off-site investigations in May and October 2000 to assess the
<br /> lateral extent of petroleum-affected soils, and to further assess groundwater conditions.
<br /> Seven soil borings were advanced around the site. Soil and groundwater grab samples
<br /> were collected based on visible evidence of petroleum impacts. At a minimum, a soil
<br /> sample was collected from near the top of the water table and a grab groundwater sample
<br /> was collected.
<br /> Soil samples were analyzed for TPHc, PNAs, and BTEX. Depths of soil sampling
<br /> ranged from 8.0 to 12.5 ft bgs. The detections of petroleum-related compounds were
<br /> limited to two borings, GMX-26 and GMX-32. TPHc was detected in both of these
<br /> borings, at 120 mg/kg at 8 ft bgs and 1700 mg/kg at 9 ft bgs, respectively. In addition,
<br /> pyrene and chrysene were identified in GMX-32, at 0.057 and 0.079 mg/kg, respectively.
<br /> Grab groundwater samples from four borings (GMX-25, GMX-30, GMX-31, and GMX-
<br /> 33) were analyzed for TPHg, TPHd, PNAs, and BTEX. These locations were all between
<br /> 10 and 100 ft downgradient of affected soils. TPHg, benzene, ethylbenzene, and PNAs
<br /> were not detected. Xylenes and toluene were detected at concentrations less than 2 mg/L
<br /> in GMX-30 and GMX-31. TPHd was detected in all samples analyzed without the silica
<br /> gel preparation, at concentrations from 86 to 560 µg/L, but not detected in any sample
<br /> with the cleanup method.
<br /> The study completed in December 2000 concluded that the lateral extent of affected soil
<br /> on the eastern, western, and southern portions of the property has been delineated.
<br /> However, additional investigation of the affected soils and groundwater north of GMX-
<br /> 32 was recommended by Geomatrix Consultants. The revised Health Risk Assessment
<br /> was approved by the DTSC in July 2002.
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