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a Project No S8080-06-02 May 5, 1995 Investigative work completed at the site through June 1992 by Uriah revealed the presence of ' residualin it beneath the central and southern portions of the site with the TPHg and TPHd so be a ' northern,`eastern and portions of the western plume limits undelineated Between approximately January and June of 1993, Uriah installed one vapor extraction well (VW-1) and a catalytic oxidation based soil remediation system The vapor extraction system (VES) was permitted by the San Joaquin Valley Unified Air Pollution Control District to operate at a maximum process flow of 55 cubic feet per minute The VES was operated intermittently between June 1993 and March 1994 by EPM Technologies (EPM) of Modesto, California and according to 'EPM, approximately 3,333 pounds of TPHg was extracted from soil via vapor extraction well VW-1 In April 1994, EPM advanced two soil borings (DTBI and DTB2) for the purposes of collecting and analyzing soil samples to evaluate the effectiveness of the VES Barings DTB 1 and DTB2 were drilled approximately two feet east of previously drilled borings EB-11 and EB-8, respectively Test results showed a reduction of TPHg, TPHd and benzene concentrations beneath the southwest portion of the site from 11,000, 2,400 and 46 mg/kg (boring EB-11 at 25 feet bgs)to less than the irespective test method detection limits (boring DTB1 at 25 feet bgs) Analytical results for a soil sample collected from 25 feet bgs in boring DTB2 also showed a reduction of TPHg, TPHd and benzene concentrations from 5,000, 2,200 and 6 2 mg/kg (boring EB-8 at 25 feet bgs) to 2,600 mg/kg (TPHg) and less than the test method detection limits (TPHd and benzene) In July 1994, Geocon performed a limited soil gas survey, advanced five soil borings(GB-1 through ' GB-5) to depths ranging from 50 to 55 feet bgs and submitted soil samples for chemical analysis The soil gas survey involved the advancement of 10 soil gas collection probes to depths ranging ' from eight to 28 feet bgs,the collection of 15 discrete depth soil gas samples and the onsite analysis for TPHg and BTEX using a mobile laboratory provided by Transglobal Environmental ' Geochemistry Nine of the 15 soil gas samples exhibited non-detectable levels of TPHg and BTEX and six samples exhibited detectable levels of TPHg at concentrations ranging from two to 36 ppmV Given the known concentrations and locations of residual TPHg and BTEX in vadose zone 1 -7-