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' ESTER 1 GEOLOGIC RESOURCES , INC . J.Munoz/3 Apr 1989 4,. Ilk Since the three existing monitoring wells are only screened inJ the saturated zone, monitoring well MW-4, proposed in the 30 March 1988 report-' _ �'j 5 would also be partially screened in unsaturated material when instalIed`` Proposed remediation options for hydrocarbons remaining in the subsurface were outlined. 79 Jima 1988 - Gordon Boggs. RWOCB - CVR In a response to comments from the RWQCB - CVR, WA presented a workplan for additional subsurface investigation. The workplan was to address a revised location of monitoring well MW 4, which would be placed closer to the high concentration of hydrocarbons detected at the southwest corner of the excavation, and how further excavation would effectively remove soils containing hydrocarbons in both the unsaturated and saturated zones. The revised location of well MW-4 is presented in Figure 6. The well _ would be screened in unsaturated soils, if water-bearing sediments were - located above 25 ft below grade. A concern was expressed that low- permeability clays between 6 and 7 ft below grade may contain hydrocarbons, which could be carried down to groundwater, if the well was screened above the water-bearing zone. y The protocol for additional excavation included removal of all soil containing observable hydrocarbons to a depth of 23 to 24 in the southwest corner of the pit and analysis of 20% of samples collected from every 15- ft by 15-ft section of exposed wall . -0 11 August 1988 - Julian Munoz. Safeway Betwe ,r2fi -and-28— Uy,WA--c-onducted_ 4d4itional excavation and soil sampling. One-hundred and fifty cubic yards of hydrocarbon-bearing soil were `removed half-way along the southern and western walls of the excavation to a depth of about 24 ft and stockpiled with the pea gravel . At that time, groundwater was at 23 ft in the monitoring wells. Soil samples TP-16 through TP-22 were collected from the floor and walls of the excavation and three composite pea gravel samples were also collected from the stockpile for analysis by Clayton Environmental Consultants (CEC) of Pleasanton, California. Soils collected from the excavation contained between less than 10 ppm to 3700 ppm TPH. Analytic results are presented in Table 1 . The pea gravel samples contained between 29 ppm to 180 ppm TPH. Analytic results are presented in Table 3. WA concluded that the highest concentrations of TPH occurred from about 15 ft below grade to a depth greater than previously determined and not defined by this investigation. 07611 ma9 C