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Work Plan for Additional Site Assessment ARCO Facility No.5469 Stockton,California Page 4 The wells will be installed to a depth of approximately 17 feet below first encountered groundwater, which is expected to occur at approximately 38 feet bgs based on the fourth quarter 2000 sampling event. The well screen will consist of 25 feet of 0.02-inch factory slotted PVC, installed from approximately 30 to 55 feet bgs. A filter pack of#3 sand will be placed in the annular space around the well screen from the bottom of the screen to a r � r maximum to two feet above the top of the screen. Two feet of bentonite will be placed on top of the filter pack to provide a sanitary seal for the well. The borehole will be backfilled with neat cement up to surface grade. A traffic rated vault box will be placed over the well and a water-tight locking cap will be placed on the top of the well. This well completion is similar to the existing groundwater monitoring wells. The actual well construction may be modified in the field,based on conditions encountered at the time of the investigation. The initial 5 feet of each boring will be advanced with a hand auger and/or posthole digger to reduce the possibility of damaging underground utilities. Soil samples will be collected at 5-foot intervals during the advancement of the borings using a California-type, split-spoon sampler equipped with three precleaned brass tubes. The ends of the bottom-most, intact tube from each sample interval will be lined with TeflonTm 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). Delta will record PID readings, soil types, and other pertinent geologic data on the borehole log. A minimum of three soil samples from each boring will be submitted for chemical analysis; the sample exhibiting the highest PID response, the sample from just above first-encountered groundwater, and the sample from the bottom of the boring. Additional samples may be collected at the discretion of the registered geologist overseeing the project. Development of the monitoring wells will consist of surging with a surge block and pumping. Development will continue, to the extent practical, until the development water runs clean and pH and conductivity measurements stabilize. After well development and stabilization of the water levels, water levels and the quantity of well volumes removed from the well will be recorded. The elevation of the top of each well casing will be surveyed to the nearest 0.01 vertical feet under the direction of a California licensed surveyor. CAARCO154691Work Plan15469wrkpin.doc Delta 3/19/2001