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U-Haul#709-50 Preliminary Site Conceptual Model Blaes Environmental December 15,2006 . 5 0 CONCLUSIONS Based on laboratory analytical results, the vertical extent of petroleum hydrocarbons in soil in the former UST area appears to be approximately 125 feet bgs since only total xylenes concentrations were detected dust above the method detection lirrut of 0 005 mg/kg at that depth and no constituents of concern were detected in soil sample DP7-150' above method detection linuts Soil bonng DP8 appears to be located on the lateral edge of petroleum hydrocarbon impacted soil and defines the lateral extent of hydrocarbons in the western dispenser area as seen by the low level TPHg and BTEX concentrations observed in the soil samples collected from 60 and 80 feet bgs The vertical extent of hydrocarbons in the western dispenser area appears to be approximately 150 feet bgs based on the decreasing BTEX (specifically total xylenes) concentrations observed in the soil samples collected from soil boring DP8 Verbal approval to cease vertical characterization activities in the western dispenser area (DP-8) based on the mobile laboratory results was obtained in the field on March 8, 2006 from Mr Michael Infurna from the San Joaquin County Environmental Health Department • Based on laboratory analytical results from all soil assessment activities conducted at the site to date, it appears that the vertical and lateral extent of hydrocarbon impacted soil at the U-Haul site has been completed successfully The following observations are based on laboratory analytical results from the additional groundwater assessment activities conducted in March 2006 and the subsequent groundwater monitoring events (including the additional groundwater monitor wells MW-13B,MW-I3C,MW-14B, and MW-14C) • Total Petroleum Hydrocarbons—Gasoline Range The lateral extent of TPHg in groundwater in the shallow (B) zone and deep (C) zone appears to be defined by monitor wells MW-5(B&C), MW-8(B&C),MW-IO(B&C), MW-I I(B&C),MW-12(B&C),MW-13(B&C),and MW-14(B&C) • Total Petroleum Hydrocarbons — DieseI Range The Iateral extent of TPHd in groundwater in the shallow (B) zone appears to be defined by monitor wells MW-5B, MW-8B, MW-IOB, MW-11B, MW-12B, MW-13B, and MW-14B The lateral extent of the majority of the mass of TPHd in groundwater in the deep (C) zone appears to be largely defined by monitor wells MW-5C, MW-8C, MW-10C, MW-1IC, MW-12C, MW-13C, MW-14C, and soil boring DP-9, however, low concentrations of TPHd ranging from 72 to 330 ppb were detected in the above listed monitor wells with the exception of MW-13C Page 22