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California R"onal Water Quality �ntrol Boar Central Valley Region �6; — `. c Sr Peter M.Rooney Sacramento Main Office Ed J.Schnabel Secretaryfor Internet Address: http://www.swrcb.ca.gov/—rwqcb5/home.html Chair Environmental 3443 Routier Road,Suite A,Sacramento,California 95827-3003 Protection Phone(916)255-3000•FAX(916)255-3015 TO: Gordon L. Boggs FROM: Mark R. List UST Program Manager Engineering Geologist DATE: 23 September 1998 SIGNATURE: SUBJECT: FILE REVIEW FORS FURTHER 0 S. CHEROKEEACTION LANE�ODI, AN JOAQUQUIRED �COUNTY ELLIS CAR WASH, At the request of the San Joaquin County Environmental Health Division(SJCEHD), a file review was completed to determine if Regional Board staff agree with the SJCEHD determination of no further action required at this site. This information was obtained during my review of the Regional Board casefile,the SJCEHD casefile, and following extensive discussions with Mr. Harlin Knoll of SJCEHD. Background: On 13 November 1990, four underground storage tanks (USTs), one 10,000-gallon gasoline, one 5,000- gallon gasoline, one 4,000-gallon diesel, and one 3,500-gallon diesel and the associated piping were removed from the Ellis Car Wash site. At the time of tank removal,tank excavation soil samples were collected. Results of the soil sample analyses detected elevated concentrations of TPHg,benzene and toluene. TPHg was detected at concentrations as high as 900 ppm(mg/Kg), BTEX constituents were detected at lower concentrations. Based on the excavation sampling results,the site was placed in the Local Oversight Program(LOP), and SJCEHD required that characterization activities be completed. On 15 May 1991, an overexcavation was completed at the site to a total depth of 18 feet below ground surface (bgs).Residual soil contamination was apparent in the sidewalls and floor of the excavation. Confirmation soil samples were collected from the overexcavation area. One soil sample collected from the southeast corner of the excavation area at 12 feet bgs, contained TPHg at 11,000 ppm(mg/Kg). Benzene was detected as high as 71 ppm, in the soil sample collected from the bottom, southwest area of the excavation. Three soil probe borings were advanced to 15, 15 and 30 feet bgs during 27 February 1997 field activities. Two of the three soil probe borings did not reach the desired depth due to refusal at 15 feet bgs.The analytical results of the soil probe borings revealed elevated concentrations of TPHg and BTEX at 15 feet bgs in one boring, located the area of the former UST.No MTBE was detected in any of the soil samples. On 6 March 1997, one soil boring was drilled using hollow-stem augers in the former UST excavation area,to collect soil samples to a total depth of 35 beet bgs. This soil boring was located near the area where the soil probe boring rig experienced refusal. Soil samples collected at 20, 30 and 35 feet bgs did not contain elevated concentrations of TPHg,BTEX or MTBE above the laboratory reporting limits. California Environmental Protection Agency er?Recycled Paper