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Sod 61-42601;Wpprt Issued: FEB 3 1997 Report 402.331-87.4 PACIFIC GAS AND ELECTRIC COMPANY DEPARTMENT OF ENGINEERING RESEARCH 3400 Crow Carryon Road San Ramon, California 94583 LABORATORY TEST REPORT SUBJECT: TRACY SERVICE CENTER SUBSURFACE TANK LEAKAGE INVESTIGATION Introduction DRAFT On November 14, 1986, PG&E's Department of Engineering Research (Civil Unit), at the request of Mike Bennett (regional environmental coordinator) of the San Joaquin Valley Regional Office, conducted a limited "in house" subsurface tank leakage investigation at the Tracy Service Center. The Service Center is located at 502 East Grant Line Road, Tracy (figure 1). Within the Service Center, the area of concern is a fuel storage tank situated in the northwestern corner of the property. The tank and pump facility is now inoperative and the fuel tank has been evacuated except for six inches of residual liquid. The fuel tank is of single wall steel construction with a storage capacity of 1500 gallons. While in service (the date of installation is unknown), the tank had stored both leaded and unleaded gasoline. The general arrangement of the tanks, pumps, and filler pipes is shown on the Site Plan, (figure 2). Recent (November 1986) excavations of the fuel tank backfill (in preparation for removal) disclosed the 'odor of hydrocarbons in the backfill soil. The purpose of this investigation was to ascertain the vertical extent and concentrations of hydrocarbons, if any, in the tank backfill and determine if any escaped hydrocarbons had intercepted the water table. Site Geography and Geology The Tracy Service Center is situated within the northwestern part of the San Joaquin Valley between the San Joaquin River and the Coast Ranges. This region is semi-arid to arid and includes flat, rolling, and mountainous terrain. The Service Center is situated on Recent deposits of river and fan alluvium (CDMG, 1966; Hotchkiss and Balding, 1971). These sediments were primarily deposited during the flood stages of major streams in the area. This alluvial material consists of unconsolidated clay, silt, sand and gravel. Hydraulically, the alluvium in the vicinity of Tracy varies from permeable to moderately permeable. Ground water within 10 feet of the land surface occurs under a large part of the Tracy area. This shallow water table lies entirely within the flood plain and fan alluvium deposits (Hotchkiss and Balding, 1971). Distribution: DGAday SChaewsky DATE P 1967 - MRLafferty TESTED BY RAMccurdy APPR O V E D LEMcMillan FILE NO. 4Q2-331 I,Swansan 1582A/mrp7 (6739)