|
Mr. M.Scott Mansholt ChevronTexaco January 13,2005
<br /> Soil and Groundwater Investigation Report--Pombo Property Page 2 of 8
<br /> (December 2000)'. Historical sampling locations associated with these investigations are included on
<br /> Figure 2, historical soil analytical results are presented in Table 1 and on Figure 3. Historical grab
<br /> groundwater analytical results are presented in Table 2 and on Figure 4.
<br /> Two of the four soil borings advanced by ESC(June 1999)exhibited petroleum hydrocarbon affected
<br /> soils. Total petroleum hydrocarbons quantified as crude(TPHc),toluene,xylenes,and polynuclear
<br /> aromatic hydrocarbons(PAHs)were detected in soils from borings EB-7 and EB-9,at depths of 9.5 and
<br /> 15 feet below ground surface(bgs),respectively. There were no observed impacts in the other two
<br /> borings,therefore they were not sampled.
<br /> Based on these findings,Geomatrix advanced 15 soil borings in tate September 1999. Evidence of
<br /> petroleum impacts was observed in eight of these borings,between depths of 7 and 19 feet bgs. Soil
<br /> samples were collected from four of the eight impacted borings(GMX-2, GMX-6, GMX-7, and
<br /> GMX-13),and analyzed for TPH as diesel (TPHd);TPH as gasoline(TPHg);TPHc; methyl tertiary butyl
<br /> ether(MTBE); benzene, toluene,ethylbenzene, and xylenes(BTEX); and PAHs. TPHd, TPI-Ig,and
<br /> TPHc were detected in all four samples. The maximum detection was 18,000 milligrams per kilogram
<br /> (mg/kg)TPHc at 8.5 feet bgs at GMX-2. Benzene, toluene, and MTBE were not detected;however,
<br /> ethylbenzene,xylenes,and PAHs were detected in low concentrations in two of the four samples.
<br /> Confirmation samples taken above the water table(from 11 to 12.5 feet bgs)from seven borings outside
<br /> the area of visibly affected soils(GMX-1, GMX-3, GMX-4,GMX-8, GMX-15,GMX-17,and GMX-19)
<br /> had no detections of BTEX,MTBE,or PAHs. Concentrations of TPHg, TPHc,and TPHd were either
<br /> non-detect or below 100 mg/kg in all samples. A grab groundwater sample from beneath affected soil
<br /> was collected in one boring(GMX-6)and analyzed for BTEX,MTBE,and PAHs. Two PAHs were
<br /> detected,both at less than 1 microgram per liter(µg/L). The Department of Toxic Substances Control
<br /> (DTSC)approved the findings of the 1999 screening risk evaluation,which concluded that residual
<br /> 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 lateral extent of
<br /> petroleum-affected soils and to further assess groundwater conditions. Seven soil borings were advanced
<br /> around the site. Soil and grab groundwater samples were collected based on visible evidence of
<br /> petroleum impacts. At a minimum, a soil sample was collected from near the top of the water table and a z
<br /> grab groundwater sample was collected.
<br /> Soil samples were analyzed for TPHc,PAHs,and BTEX. Depths of soil sampling ranged from 8 to 12.5
<br /> feet bgs. The detections of petroleum-related compounds were limited to two borings,GMX-26 and
<br /> GMX-32. TPHc was detected in both of these borings,at 120 mg/kg at 8 feet bgs and 1700 mg/kg at 9
<br /> feet bgs,respectively. In addition,pyrene and chrysene were identified in GMX-32,at 0.057 mg/kg and
<br /> 0.079 mg/kg,respectively.
<br /> Grab groundwater samples from four borings(GMX-25,GMX-30,GMX-31, and GMX-33)were
<br /> analyzed for TPHg,TPI-Id,PAHs,and BTEX. These locations were all between 10 and 100 feet down
<br /> gradient of affected soils. TPHg,benzene,ethylbenzene,and PAHs were not detected. Xylenes and
<br /> toluene were detected at concentrations less than 2µg/.L in GMX-30 and GMX-31. TPHd was detected in
<br /> all samples analyzed without the silica-gel preparation,at concentrations from 86 b.g/L to 560 gg/L,but
<br /> not detected in any sample with the silica-gel preparation.
<br /> The Geomatrix investigation completed in December 2000 concluded that the lateral extent of affected
<br /> soil on the eastern,western,and southern portions of the property has been delineated. However,
<br /> additional investigation of the affected soils and groundwater north of GMX-32 was recommended by
<br /> Geomatrix. The revised Health Risk Assessment was approved by the DTSC in July 2002.
<br /> 'Geomatrix Consultants.Inc.,December 2000,"Report ol'Additional soil and Groundwater 61veslioation,Pombo Property,(San Joaquin County
<br /> APN 232-170-07),1755 West 1 Iih Street,Tracy,California",December 21,2000.
<br />
|