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i I Addendum to Work Plan October 9, 1992 A & M Market, Acampo, California QEC 92-120-1W.ADD I from below the tanks, at concentrations of 600 parts p'er million (ppm) and 1,300 ppm (samples S-14-T2W, S-14-T1W, respectively). TPHg was detected in one soil stockpile sample at a concentration of 33 ppm (sample S-0619-1). BTEX was detected in some samples at concentrations indicated in Table 1. EDB and EDC were not detected in any of the samples. Lead was detected in concentrations ranging from 6 to 14 parts per million. As an appropriate response to the initial findings Quorum proposed an excavation program to remove hydrocarbon-bearing soil from the tank ;'cavity until either hydrocarbon concentrations in soil remaining in place were acceptable to the SJCLHD or until the safe , operating limit of the equipment had been reached. On September 28, 1992, a geologist from Quorum was at the site to supervise SEMC in excavating additional soil from the gasoline tank cavity. Mr. Michael Collins of the SJCLHD was on site during excavation. SEMC used an excavator to remove soil below the west ends of former tanks T-1 and T-3 to an approximate. depth of 22-feet, which was the safe operating limit of the excavator. Soil brought to tl`e surface in the excavator bucket from each location produced hydrocarbon vapors in concentrations greater than 1,000 ppm, as measured using a photoionization detector (PID). 1, Because of this, it was judged impractical in the field to remediate hydrocarbon-bearing'soil through continued excavation. SEMC then requested that Quorum drill soil borings `around the tank cavity to begin delineating the vertical and lateral extent of hydrocarbons in soil'in order to better evaluate remedial options. ' Proposed Additional Work �i As part of our drilling program we will perform the following tasks: . • Contact Underground Services Alert at least 48 hours prior to drilling to identify public utility lines at the site; • Observe the drilling of four soil borings (B-1 through B-4) at the locations indicated on Plate 2. Soil borings B-1 through B-4 will be drilled next to the tank cavity on'the north, west, and south sides. If hydrocarbons are detected in these soil borings, up to three additional?borings (B-5 through B-7) maybe drilled approximately fifteen to twenty feet,away from the tank cavity.. During drilling we will monitor soil for levels,I of hydrocarbon vapors using a photoionization detector (PID): Soil borings will be terminated when two consecutive soil samples show no indication of hydrocarbons or at the ground- - 2 E I - :L