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WORK PLAN, ARCO PETROLEUM PRODUCTS COMPANY ARCO STATION 2133, STOCKTON, CALIFORNIA This work plan has been prepared for ARCO Petroleum Products Company (ARCO) for ARCO Service Station 2133, located at 2908 Benjamin Holt Drive in Stockton, California. The work plan will be submitted to ARCO, the San Joaquin County Local Health District (County) , and the California Regional Water Quality Control Board, Central Valley Region (Regional Board) . On May 24, 1984 , a broken in-tank leak detector at ARCO Station 2133 , resulted in a gasoline leak from the underground storage tank system. Estimates of the amount of gasoline lost are between 2,000 and 3,200 gallons. Gettler-Ryan, Inc. (GR) , and Emcon Associates (EMCON) excavated the underground tanks and surrounding soil, installed new tanks, tested all piping, investigated contamination at the site, and installed and operated a remedial-action and recovery system. GR and EMCON' s involvement at this site was terminated by ARCO, and in late January 1987, ARCO retained Brown and Caldwell (BC) to investigate the status of the contamination at the site and to prepare a plan to clean up the site to acceptable levels. During May 1987 , a preliminary site investigation was conducted at the station by BC. The objectives of the investigation were to determine groundwater gradient, groundwater and/or pieziometric levels, identify product in soil and/or groundwater beneath the site, evaluate the site geology, identify any product in nearby wells, and obtain information necessary for evaluating potential remedial actions at the site. Additional Groundwater Monitoring Wells Based on the results of the preliminary site investigation, BC has recommended the drilling of four off-site boreholes, with monitoring wells installed in the boreholes. The locations of the proposed wells are shown on Figure 1. The four monitoring wells should provide definition of the lateral extent of off-site hydro- carbon migration. The wells will be located north, northeast, east, and south of the site. If hydrocarbon product is found in these wells, additional wells will be drilled. The locations of the possible additional wells would be based on the groundwater gradient and the results of groundwater samples collected from the four new wells. The boreholes will be drilled using a truck-mounted drilling rig equipped with 8-inch-inside-diameter, 12-inch-outside-diameter hollow-stem augers. The boreholes will be an estimated 30 feet deep.