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• <br /> • ERI <br /> ENVIRONMENTAL RESOLUTIONS, INC. <br /> July 30, 1998 <br /> JUL 3 1 199$ ERI 205513 QSS <br /> • Mr Ed Ralston <br /> Tosco Marketing Company ENVIRONMENTAL HEALTH <br /> P O Box 5155 PERMIT/SERVICES <br /> San Ramon, California 94583 <br /> • Subject Quarterly Summary Report for Environmental Investigation, Second Quarter 1998, <br /> Tosco 76 Service Station 5886, 2701 March Lane, Stockton, California <br /> Mr Ralston <br /> At the request of Tosco Marketing Company (Tosco), and pursuant to correspondence from San <br /> • Joaquin County Public Health Services, Environmental Health Division (SJCPHS/EHD) dated July <br /> 24, 1997, Environmental Resolutions, Inc (ERI) is submitting this quarterly summary report for the <br /> subject site <br /> BACKGROUND <br /> The site is immediately west of Interstate I-5 on the northwestern corner of March lane and the I-5 <br /> offramp in Stockton, California, as shown on the Site Vicinity Map (Plate 1) The locations of <br /> existing underground storage tank field (UST's), dispenser pump islands, other selected site features, <br /> and surrounding properties are shown on the Generalized Site Plan (Plate 2) Properties in the <br /> vicinity of the site are generally occupied by commercial developments <br /> • <br /> Unocal Corporation purchased the land in 1967, at which time the property was vacant In 1982, <br /> Unocal constructed a service station at the site and installed three 12,000-gallon UST's to store <br /> gasoline and diesel fuels (Delta Environmental, February 6, 1996) <br /> Between July 1995 and September 1996, Unocal replaced the original UST's and associated product <br /> distribution lines, enlarged the existing tank pit to accommodate three new 15,000-gallon UST's, <br /> advanced 21 soil borings and collected soil and groundwater samples from the boririgs utilizing a <br /> geoprobe sampling system, and drilled four additional soil borings and constructed gnroundwater- <br /> monitoring wells in three of these borings The location of existing wells are showon Plate 2 <br /> Unocal initiated quarterly groundwater monitoring during December 1996 Data collected by others <br /> indicate the groundwater flow direction ranged from northwest to west and the groundwater surface <br /> was approximately 7 to 8 feet below ground surface (bgs) Concentrations of total purgeable <br /> petroleum hydrocarbons as gasoline (TPPHg) and benzene, toluene, ethylbenzene, and total xylenes <br /> (BTEX) were not detected in groundwater except for 6 micrograms per liter (ALg/L) of xylenes <br /> detected in well MW2 during December 1996 Concentrations of MTBE have been detected in each <br /> on-site well up to 20,000 jug/L (Gettler-Ryan, Inc [GRI], April 24, 1997) <br /> • 74 Digital Drive, Suite 6, Novato, California 94949 415-382-9105 (FAX 415-382-1856) <br /> Lake Forest • Novato • Seattle <br />