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' 1 1 ]t 1 til (f1 Ui, 1 (, R k tiO �1R ( k ti , IN ( ' J Munoz/3 Apr 1989 4 ' Since the three existing monitoring wells are only screened in the saturated zone, monitoring well MW-4, proposed to the 30 March 1988 report would also be partially screened in unsaturated material when installed ' Proposed remediation options for hydrocarbons remaining in the subsurface were outlined 29 June 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 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 ' 11 August 1988 - Julian Munoz, 5afewav Between 26 and 28 July, WA conducted additional 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 t 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 ' 07(iI 1 me c)