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I <br /> 1 <br /> ER! <br /> ENVIRONMENTAL RESOLUTIONS, INC. <br /> October 27, 1999 <br /> ERI 205513 QSR10 <br /> Mr Ed Ralston <br /> Tosco Marketing Company <br /> 1380 Lead Hill Road, Suite 120 <br /> Roseville, California 95661 <br /> Subject Quarterly Summary Report for Environmental Investigation, Third Quarter 1999, <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 <br /> San Joaquin County Public Health Services, Environmental Health Division (the County)dated <br /> July 24, 1997, Environmental Resolutions, Inc (ERI) is submitting this quarterly summary report for <br /> the subject site This quarterly report discusses work completed during third quarter 1999 <br /> BACKGROUND <br /> The site is located immediately west of Interstate 1-5 on the northwestern corner of March Lane and the <br /> 1-5 offramp in Stockton, California, as shown on the Site Vicinity Map (Plate 1) The locations of the <br /> existing underground storage tank(UST) field, dispenser pump 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 /> It is ERI's understanding that Unocal Corporation (Unocal) purchased the land in 1967, at which time <br /> the property was vacant In 1982, Unocal constructed a service station at the site and installed three <br /> 12,000-gallon USTs to store gasoline and diesel fuels (Delta Environmental, February 6, 1996) <br /> Between July 1995 and September 1996, Unocal replaced the original USTs and associated product <br /> distribution lines, and enlarged the existing tank pit to accommodate three new 15,000-gallon USTs <br /> Unocal also advanced 21 soil borings and collected soil and groundwater samples from the borings <br /> utilizing a Geoprobe®sampling system, drilled four additional soil borings, and constructed <br /> groundwater monitoring wells in three of these borings The locations of existing wells are shown on <br /> Plate 2 <br /> Unocal initiated quarterly groundwater monitoring during December 1996 Data collected by previous <br /> consultants indicate the groundwater flow direction ranges from northwest to southwest and the <br /> groundwater surface ranges from approximately 5 to 9 feet below ground surface (bgs) <br /> 73 Digital Drive, Suite 100, Novato,California 94949-5791 415-382-9105 (FAX 415-382-1856) <br /> Lake Forest • Novato • Seattle <br />