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Blaes Environmental Managerneirf Gic 002-70950-03 U-Hai]#709-50 Work Plan 1118/01 2 4 WELLS AT THE SITE Due to requests made by the SJC, Blaes Environmental conducted additional site characterization activities in January 2000 Additional site characterization activities included, in part, the installation of eight new monitor wells screened across two depth intervals to accommodate the higher groundwater levels With the additional monitor wells, wells at the site are now screened across three depth intervals These depth intervals include "lower" (C) well casings screened at depths ranging from approximately 60 to 100 feet bgs, "middle" (B) well casings screened at depths ranging from approximately 45 to 77 feet bgs, and "upper" (A) well casings screened at depths ranging from approximately 23 to 62 feet bgs These screened intervals accommodate fluctuations in groundwater depth that have ranged from approximately 45 to 90 feet bgs since 1993 (SOTA, 1997) Existing monitor well construction information is summarized in Table 1 2 5 ADDITIONAL SOIL INVESTIGATION In January 2000, Blaes Environmental collected soil samples from direct-push and cone-penotrometer boreholes for laboratory analysis to further define the extent of hydrocarbons in soil beneath the site In total, six boreholes were drilled at the site (DP-1 through DP-6) (Figure 3) 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, DP4,DP-5, DP-6,MW-4a, and MW-la) The source area of the hydrocarbon plume was determined to be near borehole locations DP-I 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 (Table 2) 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 (Figure 4) The source area appears to be the former western dispenser island 5