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}' ENVIRONMENTAL HEALTH DEPARTMENT <br /> °Pa�,N ro SAN JOAQUIN COUNTY <br /> LO a <br /> Donna KDirector <br /> t e torn E H S Unit Supervisors <br /> 304 East Weber Avenue, Third Floor Carl Borgman R E H S <br /> - A]Olsen,R E li S Stockton, California 95202-2708 Mike Huggins,R E H S,R D I <br /> cRtlRa�P Program Manager Telephone 209 ��$-3420 Douglas W Wilson,R E H S <br /> F° <br /> Laurie A Cotulla,R E H S Margaret Lagorio,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 2 7 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 fled 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 />