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Site Investigation Report for the i
<br /> Former UST Locations at Stockton AASF
<br /> California Army National Guard '
<br /> 5,000-gallon USTs and fuel spill area.These sites lie to the northwest/west and south of the two
<br /> former 20,000-gallon USTs,respectively. '
<br /> 3.1 Previous Investigations
<br /> 3.1.1 After the three 5,000-gallon USTs were removed in 1990 by Wallace-Kuhl, five soil samples '
<br /> were collected from beneath the tanks and shipped to a laboratory for the following analyses:
<br /> TPH-G,TPH-D, and TPH as jet fuel (TPH-J).Following UST removal,additional investigations ,
<br /> were completed to further assess and characterize the magnitude of the contamination in soil beneath
<br /> the former UST locations. The investigations determined that the petroleum impacts in soil were
<br /> limited to the former UST area and warranted the installation of three groundwater monitoring wells, ,
<br /> which were installed in 1993 to assess the condition of groundwater beneath the former USTs.The
<br /> monitoring wells (MW-1 through MW-3)have been sampled six times to date. Groundwater samples
<br /> were collected and analyzed for TPH-G, TPH-D,TPH-J,TPH as oil (TPH-0),BTEX, and methyl
<br /> tertiary butyl ether(MTBE).
<br /> 3.1.2 In February 2004,two additional borings were drilled southeast/adjacent 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 TPH-G,TPH-D,TPH-J,TPH-O,BTEX, oxygenates (tertiary amyl methyl
<br /> ether [TAME],tertiary butyl alcohol [TBA], di-isopropyl ether [DIPE],ethyl tertiary butyl ether
<br /> [ETBE],and MTBE), and lead(Figure 3-1). '
<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 TPH-G,TPH-D,TPH-J,BTEX,TAME,TBA,DIPE,
<br /> ETBE,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 TPH-D and TPH-J concentrations greater than '
<br /> 100 milligrams per kilogram(mg/kg) (Tri-Regional Board Guidelines) (RWQCB, 1990). Soil
<br /> samples from two borings had TPH-D and TPH-J concentrations of 3,500 and 5,100 mg/kg,
<br /> respectively. Soil samples collected from the other three borings contained no detectable fuel '
<br /> constituent concentrations(Versar,hie., 2004;URS,2007). Sample locations were reported in the
<br /> Versar,Inc.report as"from the bottom of the excavation;"the depths or locations,however,were not
<br /> documented. Also, any subsequent investigations or remedial actions to address the contamination
<br /> reported in sample locations 1 and 4 were not documented(no analytical data table showing the '
<br /> results of these five samples was included in the Versar,Inc.report).
<br /> 3.2 URS 2008 Site Investigation 1
<br /> 3.2.1 Soil. In March 2008,URS conducted a soil and groundwater investigation in the area
<br /> surrounding the former USTs(Figure 3-2; Table 3-1).Twelve soil borings were drilled, and soil and '
<br /> groundwater samples were collected for both on-site and off-site laboratory analysis. Analysis for
<br /> lead was performed by Method SW6010B, and analyses for VOCs and BTEX compounds were
<br /> performed by Method SW8260B. All lead concentrations reported were below preliminary reme-
<br /> diation goals (PRGs) (150 mg/kg for lead).No VOC or BTEX compounds in soils were reported in
<br /> any of the 12 borings. The only compound in soils that exceeded action levels was diesel in boring
<br /> B9, located near the south side of the excavation of the two former 20,000-gallon USTs. Diesel was ,
<br /> K:\Wprocess\00251\CA ARNG\Stockton AASF SI\FINAL\$I Rpt.dac 4 June 2008 '
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