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f <br /> MST t-R n <br /> . ENVIRO <br /> MENTAL HEALTH6EPARTMENT <br /> SAN JOAQUIN COUNTY <br /> .�o <br /> Donna K.Herazt,R.E.H.S. Unit Supervisors <br /> Director 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> Mike Huggins,R.E.H.S.,R.D.I. <br /> r• AI Olsen,R.E.H.S. Stockton, California 95202.2708 <br /> Douglas W.Wilson,R.E.H.S. <br /> • oq =o, ;Nw Program Manager <br /> Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> �! R Laurie A.Cotulla,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Mark Barcellos,R.E.H.S. <br /> MAY 27 2005 <br /> KYLE CHRISTIE DICK MATHEWS/LIZ SEWELL <br /> BP C/O ATLANTIC RICHFIELD CO TOSCO C/O CONOCO PHILLIPS <br /> 6 CENTERPOINTE DR ROOM 161 76 BROADWAY <br /> LA PALMA CA 90623-1066 SACRAMENTO CA 95818 <br /> San Joaquin County Environmental Health Department (EHD) is the lead agency <br /> providing oversight for investigation and cleanup of releases from underground <br /> storage tanks (UST) within San Joaquin County. In 1986, the USTs owned and <br /> operated by Mobil Oil Corporation at the above referenced site failed a <br /> precision/leak test and an unauthorized release report was filed. On August 19, <br /> 1986, four USTs were removed from the site and new USTs were installed. To <br /> determine the extent of contamination caused by the unauthorized release, a soil <br /> and groundwater site assessment began. <br /> Four monitoring wells (MWs) were installed in 1986 and soil and groundwater <br /> contamination was discovered. The soil and groundwater sample analytical <br /> results evidenced total petroleum hydrocarbons as gasoline, benzene, toluene, <br /> ethyl benzene, and xylene. To investigate the lateral extent of the contamination, <br /> four MWs were installed in 1987. In 1991 six additional wells were installed to <br /> further define the lateral extent of the shallow groundwater contamination. To <br /> date, 14 MWs have been installed with total depths of 20 feet below ground <br /> surface (bgs). Quarterly groundwater monitoring of these wells has been <br /> conducted. <br /> A National Pollution Discharge Elimination System (NPDES) permit was obtained <br /> and in May of 1992 a groundwater pump and treat system was installed at the <br /> site. BP Oil Company was operating the USTs at the site at this time and <br /> performing cleanup. Floating petroleum hydrocarbon was documented on the <br /> northeast portion of the site near MW-3, MW-5, and AMW-6. The pump and treat <br /> method of remediation was used to cleanup the groundwater in the area of <br /> highest contaminant concentrations until the end of 1996. <br /> Post remediation monitoring continued quarterly and later in 1996 the <br /> concentrations of MTBE in groundwater samples collected from MW-2 and <br /> AMW-5 increased significantly, indicating there had been an unauthorized <br /> release from the UST system operating at that time. EHD recently filed an <br /> unauthorized release report for that release and created a second case for this <br /> facility. Tosco was the permitted owner/operator of the UST system at that time. <br />