SITE INFORMATION AND CORRESPONDENCE CASE 1

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STATE OF CALIFORNIA-Environmental Pro n Agency CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD PETE WILSON,Governor CENTRAL VALLEY REGION ( 3443 Routier Road, Suite A I Sacramento,CA 95827-3098 PHONE: (916)255-3000 FAX:(916)255-3015 17 August 1993 John Rutherford Desert Petroleum P.O. Box 1601 Oxnard CA 93032 CONCURRENCE WITH REQUEST FOR CLOSURE, DESERT PETROLEUM, 950 EAST ELEVENTH STREET, TRACY, SAN JOAQUIN COUNTY On 12 April 1993, the San Joaquin County Public Health Services wrote to the Regional Boardi _requesting closure for this site. Staff review of the file shows that, according to the 25 July 18 Soil and Ground Water Investigation Report, the site area is built upon deposits of brown clayey silts, which is intermixed with, and above, deposits of silty sand, sand, sandy gravels, and some clay layers. Ground water at the site is usually found at about 12 feet below ground surface (BGS), with the ground water gradient fluctuating between northwest and northeast. In April 1988, four underground storage tanks, three gasoline (10,000, 7,500, and 5,000 gallons) and one waste oil, were removed from the site. Over excavation of the pits was done to non-detect for BTEX and TPH (which was about 14 feet BGS for the fuel tanks pit and 9 feet BGS for the waste oil tank pit), but some total lead (12.8-16.7 ppm) was detected in the walls of the waste oil tank pit. Contaminated soil was taken to the Tracy Landfill. New double-walled fiberglass tanks were installed in the fuel tanks pit on 1 June 1988 and both pits filled with clean material. On 5 and 6 April 1988, three soil borings were drilled around the excavation pits to 29 feet BGS. Two soil samples were taken from each boring, at about 15 and 29 feet BGS. The samples were non-detect for BTEX, TPH, ethylene dibromide, and organic lead. These soil borings were converted to ground water monitoring wells. Table 1 on the following page summarizes the history of ground water monitoring from these wells (monitoring well 1 is downgradient of the pits). According to the 25 March 1993 Site Closure Report, on 11 March 1993 two additional soil borings were drilled to further determine the extent of soil and ground water contamination. Soil boring SB- 1, located immediately west of the gasoline tanks excavation pit, was drilled to 12 feet BGS. A soil sample from this boring taken at 10.5 feet BGS was non-detect for BTEX (detection limit 5 ppb) and TPH-G (detection limit 1 ppm). Soil boring MW-4, which was north of the excavation pits and drilled to 15 feet BGS, also was non-detect for BTEX and TPH-G in the soil at 10.5 feet BGS. Soil boring MW-4 was also converted to a monitoring well, and the results of sampling are shown on Table 1.