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U-Haul#709-50 Blaes Environmental Preliminary Site Conceptual Madel December 15,2006 10 Results of the October 1995 quarterly monitoring and sampling event indicated that the depth to groundwater was between approximately 63 to 66 feet bgs and the groundwater flow direction was toward the southwest Analytical results indicated that hydrocarbon concentrations exceeded California action levels in groundwater samples from five of the seven on-site monitoring wells (Table 2) Results also indicated that elevated hydrocarbon concentrations were present in groundwater from the off-site monitoring well MW-7 Between November 1994 and September 1997, SOTA conducted groundwater monitoring at the site During this period,the screen intervals of the on-site monitor wells became submerged (Appendix B) In January 2000, Blaes Environmental collected soil samples from direct-push and cone-penetrometer boreholes for laboratory analysis to further define the extent of hydrocarbons in soil beneath the site In total, six boreholes were drilled during the January 2000 event (DP-1, DP-2, DP-3, DP-4, DP-5 and DP-6) This investigation involved collecting soil samples within saturated soil to approximately 126 feet bgs (or approximately 77 feet below the groundwater interface)at that time Direct-push and cone-penotrometer soil sampling technologies were determined to be the best methods for preserving soil sample integrity when sampling below groundwater Soil samples were also collected from soil borings to complement data collected from the direct-push/cone-penetrometer boreholes Soil sample locations included the central portion of the hydrocarbon plume (DP-1, DP-2 and MW-3a) and the lateral portions of the plume (DP-3, DP-4, DP-5, DP-6, MW4a, and MW-1 a) The source area of the hydrocarbon plume was deterrmned to be near borehole locations DP-1 and DP-2 Analytical results indicate that total petroleum hydrocarbons as gasoline (TPHg) concentrations in soil from DP-2 were greater than 1,000 milligrams per kilogram (mg/Kg) at depths of 10 to 74 feet bgs Soil collected at approximately 29 feet bgs contained 21,000 mg/Kg TPHg Field observations of this sample indicated that apparent free-phase hydrocarbons saturated the sample The apparent source area of hydrocarbons in soil is also defined by plotting the vertical representation of soil sample analytical results The source area on the U-Haul property appears to be the former western dispenser island The lateral extent of hydrocarbons in soil was better defined with analysis of soil samples collected from boreholes DP-3 and DP-6 Borehole DP-3 defined the northern lateral extent of hydrocarbons in soil with detectable concentrations of TPHg less than or equal to 10 mg/Kg and detectable benzene concentrations less than 0 72 mg/Kg Soil from this borehole did not contain detectable concentrations of hydrocarbons at depths of 70, 100, and 110 feet bgs Page 6