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� v 8 A S S O C I A T E S I N C summarized in Table 1 Laboratory data sheets and chain-of-custody documentation for soil samples are presented in Appendix B 4.2 Petroleum Hydrocarbons in Groundwater ' The grab groundwater samples collected from borings SB28, SB29, and SB30 contained elevated concentrations of TPHg, TPHd, and/or BTEX The grab groundwater samples collected from borings S1331, SB32, SB36, and SB37 contained low to non-detectable concentrations of TPHg, ' TPHd, and/or BTEX Concentrations of benzene exceeded the California Maximum Contaminant Level (MCL) in borings SB28, SB29, S1330, SB36, and SB37 Concentrations of toluene, ethylbenzene, and xylenes exceeded their respective MCLS in boring SB28 only The groundwater samples collected from borings SB28, SB29, S1330, SB31, SB32, S1335, SB36, and SB37 contained detectable concentrations of MTBE Concentrations of MTBE exceeded the drinking water action level of 13 ppb and the secondary MCL of 5 ppb in all of these borings except SB32 and/or SB35 Isoconcentration Maps showing the TPHg, TPHd, and MTBE concentrations in groundwater are shown on Figures 7, 8, and 9, respectively These figures include the analytical results of groundwater samples collected from the six on-site groundwater monitoring wells in June 1999 Analytical results of grab groundwater samples are summarized in Table 2 Historical analytical results of groundwater samples collected from the on-site groundwater monitoring wells are ' summarized in Table 3 Laboratory data sheets and chain-of-custody documentation for groundwater samples are contained in Appendix B 5.0 DISCUSSION ' Soil borings advanced along the levee, southwest of the location of the former USTs and the current AST location contained elevated concentrations of TPHg, TPHd, and MTBE As shown on Figures 4, 5, and 6, the concentrations of TPHg, TPHd, and MTBE in soil were greatest in ' borings SB28, SB29 and SB30 adjacent to the former product lines The highest concentrations were detected in the soil samples collected from 10 feet bgs Soil samples collected from 15 feet bgs contained very low to nondetectable concentrations The extent of impacted soil has been t defined and generally extends along the backside of the levee, west of the store The areal extent is approximately 200 feet in length and 65 feet in width and is limited to depths between 5 and 15 feet bgs Additionally, MTBE impacted soil extends east of boring SB28, between the store and office building, and was detected in boring SB31 As shown on Figure 7, the TPHg plume in groundwater generally extends along the backside of ' the levee, west of the store, and is approximately 225 feet long and 70 feet wide Concentrations are highest in boring SB28, adjacent to the former and current product lines The extent of TPHg in groundwater has not been fully defined to the west and south but samples from borings SB36 and SB37 contained low concentrations of TPHg (130 to 190 ppb) indicating that these borings w 1625141reportslsuminv doc 6