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INTRODUCTION This work plan presents the proposed scope of work for groundwater assessment at Pacific Gas and Electric Company's (PG&E's) McDonald Island Gas Storage Facility, San Joaquin County, California. A site vicinity map is shown on Figure 1, and a site plan is included as Figure 2. The proposed scope of work will be conducted in accordance with the guidelines and requirements of the SJCPHS and the Regional Water Quality Control Board,Central Valley Region(RWQCB) and will include the following tasks: • Obtain a drilling permit from the SJCPHS. • Drill soil borings using a hand auger or direct-push drill rig to collect soil and grab groundwater samples for laboratory analysis. • Analyze soil and groundwater samples for specified hydrocarbon constituents. • Evaluate the data and prepare a report that will include the discussion of findings and recommendations for subsequent investigation,if any. BACKGROUND During soil excavation activities for the installation of a replacement valve at PG&E's compressor station,hydrocarbon odors were noted by construction workers. The valve was replaced,but the excavation was left open pending the results of soil sampling and assessment activities. On August 22,2001, five soil borings, SB-1 through SB-5,were drilled to depths of nine feet. Soil samples were collected from the borings at depths of three, six, and nine feet with the exception of Boring SB-6,which was drilled at the bottom of the excavation beginning at approximately six feet below grade. During drilling, groundwater was encountered at approximately 10 feet below grade in Boring SB-6. Additionally, eight soil samples, SW-1 through SW-8,were collected from the sidewalls of the excavation and eight soil samples, SP-1 through SP-8,were collected from stockpiled from the excavation. All soil samples were analyzed for total petroleum hydrocarbons in the gasoline,kerosene, diesel,and motor oil ranges as well as for benzene, toluene, ethylbenzene, and total xylenes. The soil sample with the highest concentration of petroleum hydrocarbons and the soil sample with no detectable hydrocarbon concentrations were also analyzed for CAM 17 metals. Analysis of the soil samples collected from the borings detected up to 18 milligrams per kilogram (mg/kg) total petroleum hydrocarbons as diesel (TPH-D) and 830 mg/kg total petroleum hydrocarbons as motor oil (TPH-MO). Concentrations detected in the sidewall samples were up to 53 mg/kg total petroleum hydrocarbons as gasoline (TPH-G), 67 mg/kg TPH-D, and 440 mg/kg TPH-MO. With approval of the San Joaquin County Public Health Services (SJCPHS), stockpiled soil was used to backfill the excavation. JDIU U 1