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June 21, 1993 Working To Restore Nature <br /> ARCO Service Station No 2130 <br /> ` literature indicates that mass removal indicators are the preferred parameters for the <br /> selection of sparge influences <br /> BACKGROUND <br /> I <br /> iSite DescriRtion <br /> 1` �C <br /> ARCO Service Station No 2130 is at the northeast corner of Hammer Lane and El Dorado <br /> Street in Stockton, California, as shown on the Site Vicinity Map (Plate 1) According to <br /> information supplied by ARCO, there are four underground storage tanks at the site two <br /> �C 4,000-gallon tanks store unleaded gasoline, one 6,000-gallon tank stores super unleaded <br /> gasoline, and one 10,000-gallon tank stores unleaded gasoline The approximate tank <br /> i <br /> locations relative to site structures are shown on the Generalized Site Plan (Plate 2) <br /> Previous Wo <br /> r <br /> Work performed at the site between June 1991 and August 1992 included drilling 16 soil <br /> borings and installing 10 vapor-extraction wells and five ground-water monitoring wells <br /> (RESNA, Problem Assessment Report, preparation in progress) The locations of borings, <br /> I <br /> I ground-water and vapor-extraction wells are shown on Plate 2 Results of the investigations <br /> indicated residual total petroleum hydrocarbons as gasoline (TPHg) were present in soil in <br /> the vicinity of the existing underground storage tanks (UST's) from approximately 15 to 61 <br /> i� <br /> feet below surface grade (bsg) Periodic ground-water monitoring was iruttated at the site <br /> in January 1992; results from January 1993 sampling indicates that dissolved TPHg was <br /> present in ground water beneath the site at concentrations ranging from 79 to 1,800 parts <br /> per billion (ppb) <br /> 41 Cr <br /> 30003-8 3 <br /> I <br /> I _ <br />