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• ERI <br /> FIi1V1F1ONMFRITAt RESOLUTIONS, INC. <br /> April 28, 1998 <br /> ERI 205513 QS4 <br /> Mr Ed Ralston <br /> Tosco Marketing Company <br /> P O Box 5155 <br /> San Ramon, California 94583 <br /> Subject Quarterly Summary Report for Environmental Investigation, First Quarter 1998, <br /> Unocal 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 (PHSIEHD) dated July 24, <br /> 1997, Environmental Resolutions, Inc (ERI) is submrttmg 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 1-5 <br /> offramp in Stockton, California, as shown on the Site Vicinity Map (Plate 1) The locations of <br /> existing underground storage tanks (USTs), dispenser islands, other selected site features, and <br /> surrounding properties are shown on the Generalized Site Plan (Plate 2) Properties in the vicinity of <br /> the site are generally occupied by commercial developments <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 borings utilizing a <br /> geoprobe sampling system, and drilled four additional soil borings and constructed groundwater <br /> monitoring wells in three of these borings The location of existing wells are shown on PIate 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 (ug/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 ppb (Gettler-Ryan, Inc [GRI], April 24, 1997) <br /> 74 Digital Drive, Suite 6, Novato, California 94949 415-382-9105 (FAX 415-382-1858) <br /> Irvine 9 Novato a Seattle <br />