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California Ronal Water Quality ( ontrol Board <br /> vCentral Valley Region t <br /> Steven T.Butler,Chair <br /> Winston H.Hickos Gray Davis <br /> Secretaryfor Sacramento Main Office Governor <br /> Environmental Internet Address: http://vn v.sw cb.ca.gov/—nvgcb5 <br /> Protection 3443 Rou6cr Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> TO: Gordon L. Boggs FROM: Marty Hartzell <br /> UST Program Manager Associate Engineering Geologist <br /> DATE: 14 March 2000 SIGNATURE: 3 "1 Y gi�� <br /> 6-1 <br /> SUBJECT: NONCONCURRENCE WITH SAN JOAQUIN COUNTY'S NO FURTHER <br /> ACTION REQUIRED DETERMINATION, <br /> ARCO #6100, 25775 PATTERSON PASS ROAD, TRACY <br /> On 13 January 2000, I met with Ms. Margaret Lagorio of the San Joaquin County Environmental Health <br /> Division to discuss the subject site. Ms. Lagorio and I reviewed the 12 October 1998 Hydrocarbon <br /> Mass Evaluation submitted by Pinnacle Environmental, the 10 Sept 1999 Addendum to Hydrocarbon <br /> Mass Evaluation prepared by The IT Group (formerly Pinnacle), and the 4 January 2000 Historical <br /> Chromatogram Review of MTBE Soil Analytical for ARCO Service Station No. 6100, prepared by The IT <br /> Group. The discussion of site-specific data is presented below. On 19 January 2000, I informed Ms. <br /> Lagorio that I could not concur with site closure without groundwater analyses for petroleum <br /> hydrocarbons and fuel oxygenates. San Joaquin County Environmental Health Division (County) <br /> submitted the Case Closure Summary for ARCO #6100 (ARCO) on 2 February 2000, and I requested an <br /> extension from Ms. Lagorio on 24 February 2000. <br /> The following background and site investigation information is presented in the memo below: <br /> • Six underground storage tanks removed in 1987 to 1990. <br /> • Soil investigation conducted in 1991 to 1995. <br /> • High concentrations of TPHg and BTEX were identified in site soils. <br /> • Sixteen soil vapor extraction (SVE) wells installed(a SVE system was not installed). <br /> • On-site and offsite water supply wells, California Aqueduct within 1,200 feet of site. <br /> • Complex hydrogeology. <br /> The site is an active ARCO retail gasoline station. One waste oil underground storage tank(UST) was <br /> removed from the site in May 1987, and five gasoline USTs (2 regular and 3 unleaded) were removed <br /> from the site in November 1990. The tank pits were backfilled with pea gravel, and the site has been <br /> paved over with asphalt. Multiple soil borings were completed from 1991 through 1995, and sixteen <br /> soil vapor extraction wells were installed. A vapor extraction system was not operated at this site. Site <br /> maps from Pinnacle's Hydrocarbon Mass Evaluation are presented as Figures 1 and 2. <br /> TPHg and BTEX constituents were identified in site soils from 6 to 115 feet bgs; with the highest soil <br /> concentrations identified from 26 to 45 feet bgs. The maximum concentrations found in soil samples <br /> show TPHg at 28,000 mg/kg,benzene at 120 mg/kg, toluene at 580 mg/1, ethyl benzene at 170 mg/l, and <br /> xylenes at 870 mg/kg. Samples collected from the site have not been analyzed for MtBE or other fuel <br /> California Environmental Protection Agency <br /> Qa Recycled Paper <br />