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Work Plan • ARCO Facility No.6100 Tracy,California Page 3 Task 2: Field Activities Soil Borine One 10-inch diameter soil boring will be drilled in the right-of-way of Patterson Pass Road. The boring will be drilled using an air-rotary casing-hammer drilling rig equipped to advance the boring to a depth of 200 feet, if warranted. The initial 5 feet of the boring will be advanced with a hand auger and/or posthole digger to reduce the possibility of damaging underground utilities. Given the number of samples collected during previous investigations for laboratory analyses and soil classification purposes, soil sampling will be limited to depths of 30, 50, 70, and 100 feet bgs. Beginning at 100 feet bgs, where previous sample collection has been limited, samples will be collected every 10 feet. Samples will be collected using a California-type, split spoon sampler equipped with three pre-cleaned brass tubes. The ends of the bottom-most, intact tube from each sample interval will be lined with Teflon TI sheets, capped, and sealed. Each sample will then be labeled, placed in a resealable plastic bag, and stored in an ice-chilled cooler. The samples will remain chilled until relinquished to a State- certified analytical laboratory. Strict chain-of-custody procedures will be followed from the time the samples are collected until the time the samples are relinquished to the laboratory. Soil contained in the remaining brass tubes will be screened for volatile organic compounds using field instrumentation equipped with a photoionization detector(PID). Soil samples used for logging will be classified by the field geologist in accordance with the Unified Soil Classification System. Representative portions of the samples will be retained for further examination and for verification of the field classification. Logs of the borings indicating the depth and identification of the various strata, PID readings, and pertinent information regarding the method of maintaining and advancing the borehole will be prepared. The boring will be backfilled to the surface with a bentonite-cement slurry pumped into the boring through a tremie pipe. A minimum of five soil samples collected from the boring will be submitted for chemical analysis. Among these samples, will be the sample exhibiting the highest PID response, the sample from just above groundwater(if encountered), and the sample collected from the bottom of the boring. Groundwater Monitoring Well (if warranted) If groundwater is encountered, the boring will be completed as a 4-inch diameter groundwater monitoring well. A staff geologist will observe the construction of the groundwater monitoring well. The well will be installed to a depth of approximately 10 to 15 feet below first encountered groundwater. The actual depth may be modified in the field based on subsurface conditions. The well will be constructed using 20 feet(approximately 10 feet above and 10 feet below fust encountered water) of 0.02-inch machin slotted polyvinyl casing (PVC). Centralizes will be used when installing the PVC casing to maintain the position of the casing in the borehole. A filter pack consisting of Lonestar#3 sand will be placed in the annular space between the PVC casing and the borehole wall. Sand will be added to the borehole through the steel drive casing to provide a uniform filter pack around the casing and to stabilize the borehole. The sand pack will be placed to a maximum of 4 feet above the screen, followed by a 4-foot seal consisting of bentonite pellets. Cement grout containing 5 percent bentonite will be placed above