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6-02-1998 1 22Pt 1 FROH P 3 u , MEMORANDUM CahEPA CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD • .,,�„� CENTRAL VALLEY REGION v 3443 Routic.Road,Suitc A,sacrnmcrtto,CA 95827-3003 (916)255.3000 - CALNET$ 494-3440 - FAX(916)255-30[S 1M Wfla016Gowrner TO: Gordon L Boggs FROM: Patricia A Anderson DATE 26 May 1998 SIGNATURE SUBJECT: RENEW FOR NO FURTHER ACTIO.NREQUJ.R.E'D CONCURRENCE,FRANKS EXXON#4, 14800 W.FRONTA GE RO.41? (HWY 99% MANTEC4,SAN JOAQUIN COUNTY An investigation of the lateral and vertical extent of petzoleurn contamination vias initiated in response to the detection of petroleum hydrocarbons in the soil adjacent to the underground storage tanks In 1988 and 1989, four soil borings were advanced between 40 to 49 f}bgs and completed as monitoring wells The highest concentrations of soil coatamina,ion occurred in MW-1 and MW-2 at 15 to 25 ft below ground surface(ft bgs)with 88 mg/kg to*al purgeable (gasoline)petroleum hydrocarbons (TPPH) 0 26 mg/kg benzene,0 53 mg/kg toluene 0 31 rn&lkg ethylbenzene, 1 9 mg/kg xylene(BTEX) 0 01 mg/kg ethyldibromide,and 0 003 mg/kg 1,2 dichloroethane (1,2-DCA) This contamination . extends beyond 30 ft bgs with lower concentrations of conta=riation. Ground water samples from these wells had 200 µg11 TPPH,4 µg/i xylene, and 8 4 µg/1 ethyldibrornide In November 1989,three 10,000 gallon underground storage (regular,unleaded and dies;l)tanks (USTs) were removed and contaminated soil was excavated to 17 ft bgs Ali soil samples,collected from the pit, confirmed contamination. in /November 1989 and June 1992,five additional monitoring wells were installed Quarterly ground water sampling of the monitoring wells from April 1992 to January 1995 showed that contaminatiozi occurred consistently in MW-1 through MW4, occasionally in MW 5 through MW-8, and was nondetect in MW-9 During this penod, the maximum concentration of contamination occurred in MW-3 with 14,000 leg4 TPH-g, 5,200 µg11 TPH-d,3,700, 110, 1,000, 1,900 jAg/l BTEX MW-1 had the highest concentration(770 µg/1)of 1,2-DCA,and 280µ0f7 methyl tertiary-butyl ether(MTBE/EPA Method 8020) The excavated soil was stockpiled on site and aerated to nondetect This soil was used for landscaping Remedial action was initiated in October 1990 with the installation of soil venting components in the tank basin after the USTs were removed Two 25 ft casings were installed at 10 ft bgs beneath the product tines and two 25 ft casings were installed 17 ft bgs beneath the USTs Soil vapor and ground water extraction systems were operated from January 1995 to November 1996 During this period, these systems extracted 2,3918 lbs of TPH-g and 8 17 lbs of benzene. When the remediation systems were shut-off,the quarterly ground water sampling showed that the plume of . contamination had diminished in size with contamination being detected in MW-1 through MW-4 and provied Paper Our MU orf W fo preserve asd erJ,ona'the guatiry ofCoir,fvrna a srarar re-IOW es and efaure fdeirproper allocation and cfffcicrt=f w the benefit pf yrezenf and future generatraru