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Report on Additional Site Assessment and Soil Vapor Extraction Test 1 7-Eleven Store No 17334,4501 North Pershing Avenue,Stockton, CA August 21,2002 10 INTRODUCTION This report is submitted by Shaw Environmental, Inc (formerly known as IT Corporation) to summarize the results of site assessment conducted at 7-Eleven, Inc Store No 17334, located at 4501 North Pershing Avenue in Stockton, California (Figures 1 and 2) The scope of work included the drilling and sampling of one soil boring and two soil vapor extraction (SVE)/air sparge (AS) test wells, SVE testing, and preparation of this assessment report summarizing methods and results ' 24 BACKGROUND 21 Nearby Service Stations Based on review of San Joaquin County Public Health Services (SJCPHS) files, three sites adjacent to the subject site have had reported releases of gasoline-range petroleum hydrocarbons MCardlock Gasoline Station, 4555 N Pershing Avenue, located 100 feet west (upgradient) of the subject site Shell Service Station, 4445 N Pershing Avenue, on the southeast corner of Pershing and Rosemarie Lane (crossgradient of the subject site) Exxon Service Station, 4444 N Pershing Avenue, on the southwest corner of Pershing and Rosemarie Lane (crossgradient of the subject site) Groundwater monitoring and sampling have been ongoing at the Exxon site since 1987, and at the Cardlock and Shell sites since 1992 In 1988 Exxon installed a 30-foot-deep groundwater monitoring well (MW-9) approximately 10 feet east and 10 feet south of 7-Eleven's underground storage tank (UST) area The depth to groundwater in well MW-9 has ranged from 30 feet below grade (bg) in 1990 to 20 feet bg in April 1996 Seasonal water table fluctuations average between 2 to 3 feet Historical groundwater flow direction at the three sites has been to the northeast 22 Site History On February 20, 1997, Fluor Daniel GTI supervised the advancement of four angled and three vertical geoprobe borings (GP-1 through GP-7) at the site Soil samples were collected from the borings at depths of 15 to 22 feet bg Six borings (GP-1 through GP-6)were drilled beneath the three 10,000-gallon USTs at the site, as required by the SJCPHS prior to tank fining permit approval In addition, groundwater grab samples were collected from borings GP-3, GP-4, and GP-7 Benzene was detected in ' soil sample GP-4 @ 17 feet, at a concentration of 0 0095 milligrams per kilogram (mg/kg) Total petroleum hydrocarbons as gasoline(TPH-G) were not detected in any of the soil samples collected The highest methyl-tert-butyl ether(MTBE) concentration was reported in sample GP-1 @ 15 feet at 0 91 ' mg/kg (EPA Method 8260) i 17334sar doc