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Work Plan for the
<br /> Former Two 20,000-Gallon USTs Location at Stockton AASF
<br /> California Army National Guard
<br /> 3.1.2 In February 2004,two additional borings were drilled southeastladjacent to the former
<br /> 5,000-gallon UST location. Soil and groundwater samples were collected from the two borings(B-1
<br /> and B-2)and analyzed for TPHG;TPHD;TPHJ;TPHO;BTEX;oxygenates(tertiary amyl methyl
<br /> ether[TAME],tertiary butyl alcohol[TBA)],di-isopropyl ether[RIPE],ethyl tertiary butyl ether
<br /> [ETBE],and MTBE);and lead.
<br /> 3.1.3 Another soil boring(B-28)was drilled on February 2004 to assess the impact to soil at the fuel
<br /> spill location south of the former 5,000-gallon UST location. The boring was drilled to a depth of 46
<br /> feet bgs. Four soil and one groundwater sample(grab type)were collected from the borehole,
<br /> shipped to a laboratory,and analyzed for TPHG,TPHD,TPHJ,BTEX,TAME,TBA, DIPE, ETBE,
<br /> and MTBE.
<br /> 3.1.4 Soil samples collected during the removal of the three 5,000-gallon USTs(January 1990)from
<br /> beneath the fuel tanks within the excavation had TPHD and TPHJ concentrations greater than
<br /> 100 milligrams per kilogram(mg/kg)(Tri-Regional Board Guidelines [RWQCB, 1990]). Soil
<br /> samples from locations 1 and 4 had TPHD and TPHJ concentrations of 3,500 mg/kg and 5,100
<br /> mg/kg,respectively. Soil samples collected from locations 2,3,and 5 contained no detectable fuel
<br /> constituent concentrations(Versar,Inc.,2004).
<br /> 3.2 Nature and Extent of Petroleum Impacts
<br /> 3.2.1 Soil. During February 2004,three boreholes were drilled to groundwater depth and soil
<br /> samples were collected south of the vicinity of the previous USTs(the three 5,000-gallon and two
<br /> 20,000-gallon)as follows: B-1 was located southeast of the three former 5,000-gallon UST
<br /> excavation;B-2 is located approximately 25 feet northeast of B-1;and B-28 is located southeast of
<br /> the three 5,000-gallon USTs excavation area(see Figure 3-1).Borehole B-28 was drilled to assess
<br /> the impact to soils at the previous the fuel spill location.All three borings—B-1,B-2,and B-28—
<br /> were drilled south and southeast of the two former 20,000-gallon USTs location. Soil samples from
<br /> B-1,B-2,and B-28 were analyzed for TPHG,TPHD,TPHJ,TPHO,BTEX and oxygenates,and lead
<br /> by United States Environmental Protection Agency(EPA)Methods SW8015M, SW8260,and
<br /> SW6010B,respectively. Soil sample analysis results indicate that TPHD and TPHJ were the only
<br /> petroleum constituents detected.The maximum detected concentration of 420 mg/kg at 5 feet bgs
<br /> was reported in boring B-28 for both TPHD and TPHJ,and is greater than 100 mg/kg(the recom-
<br /> mended Tri-Regional Board guideline). The shallower sample at 2 feet bgs in boring B-28 had TPHD
<br /> and TPHJ concentrations of 130 mg/kg. However,the soil sample collected at 10 feet bgs from B-28
<br /> had no detectable TPHD and TPHJ concentrations.All remaining deeper soil samples collected in
<br /> borehole location B-28 contained no detectable petroleum constituent concentrations.
<br /> 3.2.2 These detected concentrations indicate that relatively shallow soils beneath the area of the
<br /> previous spill have likely been impacted by the spill;however,deeper samples beyond 10 feet bgs
<br /> had no detection of petroleum constituent concentrations.All the collected soil samples within
<br /> boreholes B-1 and B-2 had no detectable TPH,BTEX,and oxygenate constituent concentrations for
<br /> all the analysis performed,except in one boring(B-1)at one sample depth.An MTBE concentration
<br /> of 0.9 mg/kg was detected at 10 feet bgs in B-1,and is less than the residential preliminary remedi-
<br /> ation goal(PRG)of 32 mg/kg and the industrial PRG of 70 mg/kg(EPA,2004). Lead concentrations
<br /> were detected in soil samples from boreholes B-1,B-2,and B-28 up to a maximum concentration of
<br /> 52.3 mg/kg,which is less than the California-modified PRG of 150 mg/kg(EPA, 2004). Table 3-1
<br /> lists the soil sampling results for the collected samples within boreholes B-1,B-2,and B-28. Figure
<br /> 3-2 shows the detected concentrations in soil for each constituent at each sample depth.
<br /> KAWprocess\00251\CA ARNG\Stockton AASF WP\FINAL\WP text.doc 4 June 2007
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