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Closure Report 5 Golden Grain Manteca Bean f=acility,299 Moffat Boulevard,Manteca,California July 16,1996 ' 0 1991 Analysis of the aquifer testing data also value of 03 for the aquifer(Groundwater Technology ) y q g Indicated that the lower sand unit did not respond as confined, indicating the clay layer present at approximately 25 feet bsg is not continuous Review of the boring logs showed saturated conditions were encountered continuously from just above the clay layer, throughout the clay layer, and Into the lithology below, Indicating saturated conditions through the clay The subsurface geology and hydrogeologic data for the site indicates that there is one water bearing zone within the project scope ' 22 Baseline Site Conditions The results of the assessment work were used to characterize the vertical and lateral extent of hydrocarbon Impacted soil and groundwater at the site The following sections document the baseline site conditions prior to site remediation 2.2.1 Extent of Hydrocarbon Impacted Soil Results of the assessment indicate petroleum hydrocarbons existed in two phases In the unsaturated zone soil 1) a liquid phase adsorbed to soil particles, composed of separate-phase hydrocarbons ' and dissolved-phase hydrocarbons in pore water, and 2) a vapor phase within the soil pore space As Indicated by the results of the soil gas survey conducted at the site in 1989, the lateral extent of ' the soil vapor phase plume (figure 8)was roughly concentric around the former tank with a maximum radius of 90 feet ' The lateral extent of impacted sod was defined by the analytical results of sod samples collected during the monitoring well installations A summary of the soil sample analytical results Is presented ' in table 3 Review of the analytical results Indicate Impacted soil in the unsaturated zone extended approximately 50 feet radially away from the former tank pit (figure 9) The highest concentration of hydrocarbons was reported in soil samples collected from the bonngs for monitoring wells MWA, ' MW-2, MW-3, MW-4, and MW-7 at depths of between 15 and 20 feet bsg The vertical extent of impacted soil defined during the site characterization activities is illustrated on cross-sections A-A', ' B-B', and C-C' (figures 4, 5, and 6, respectively) The lateral and vertical boundanes of the adsorbed phase and lateral boundary of the vapor-phase plume in the unsaturated zone were successfully defined during the site assessment work 42020219CR FLUOR DANIEL GTI