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T <br /> d � <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD <br /> CENTRAL VALLEY REGION <br /> ORDER N0. 90-XX ''ll __ 1� <br /> CLEANUP AND ABATEMENT ORDER yov4. `V L►u v� <br /> FOR MAR 0 7 1990 <br /> EXXON COMPANY, U.S.A. -NwiRONUENTA.LHEA1 <br /> SAN JOAQUIN COUNTY <br /> The California Regional Water Quality Control Board, Central Valley Region <br /> (hereinafter Board) , finds that: <br /> I . Exxon Company, USA (Exxon) formerly operated a gasoline service station <br /> at 4444 North Pershing Avenue in Stockton, San Joaquin County. The site <br /> location is shown on attachment "A" which is made a part of this order. <br /> 2. Underground storage tanks were removed from the site on 24 July 1986. <br /> Petroleum hydrocarbons were found in soil beneath the tanks. <br /> 3. On 23 September 1986 approximately 300 cubic yards of contaminated soil <br /> were excavated from the former tank area. Ground water was encountered <br /> in the excavation at a depth of 21 feet below ground surface. A sample <br /> of this ground water contained 130,000 parts per billion (ppb) total <br /> petroleum hydrocarbons (TPH) , 40,000 ppb benzene, 43,000 ppb toluene, <br /> and 9,900 ppb xylene. <br /> 4. Three ground water monitoring wells (MW-1 , MW-2, nd MW-3) were <br /> installed at the site during January 1987. The Results from the first <br /> round of sampling showed that TPH were not detected in the upgradient <br /> well (MW-1 ), while the two downgradient wells contained up to 32,000 ppb <br /> TPN. <br /> 5. Since the initial ground water investigation, seven additional ground <br /> water monitoring wells have been installed on and off-site. However, <br /> the extent of ground water contamination has not yet been defined. The <br /> farthest downgradient well (MW--10) , located approximately 130 feet <br /> downgradient from the former tank area, contained 9,400 ppb TPN, 5,800 <br /> ppb benzene, 290 ppb toluene, 700 ppb ethylbenzene, and 340 ppb xylenes <br /> during the 17 August 1989 round of ground water sampling. <br /> 6. Exxon has submitted a proposal for a ground water extraction system to <br /> address the on-site ground water contamination. However, the proposal <br /> did not include any additional investigation to define the extent of <br /> contamination. <br /> 7. In a letter dated 10 October 1989 the San Joaquin County Department of <br /> Public Health Services, with Regional Board concurrence, requested that <br /> Exxon submit a work plan for defining the extent of ground water <br /> contamination. \\ <br /> J <br />