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' Quarterly Monitoring Report July 12, 1996 <br /> Chapin Brothers Automobile Repair Facility Stockton, California <br /> I <br /> ' 1.0 INTRODUCTION <br /> This report summarizes the analytical results generated during a quarterly groundwater <br /> ' monitoring event conducted by Lush Geosciences at the Chapin Brother's Automobile Repair <br /> site located at 1766 Monte Diablo Avenue in Stockton, California The property is located on <br /> the southeast corner of the intersection of Monte Diablo Avenue and Buena Vista Avenue in the <br /> City of Stockton, California (Figure 1) A service station operated on the property from the late <br /> ' 1930's until 1990 An automobile repair facility has operated on the site since that time <br /> The quarterly monitoring was conducted to collect and analyze representative <br /> groundwater samples to help evaluate concentrations of total petroleum hydrocarbons as gasoline <br /> (TPHg) and purgeable aromatic hydrocarbons (benzene, toluene, xylenes and ethylbenzene <br /> ' (BTEX)) in uppermost groundwater at the site <br /> ' PREVIOUS WORK <br /> Because of a suspected release from the underground fuel storage tanks, a single <br /> monitoring well was installed at the site on December 5, 1990 by Roger Foott Associates, Inc of <br /> West Sacramento, California Subsequent laboratory analysis of a sample from the well <br /> determined that shallow groundwater beneath the site had been impacted with gasoline On <br /> August 4, 1993 one 550-gallon waste oil tank, two 4,000-gallon unleaded gasoline tanks, and <br /> two 8,000-gallon unleaded gasoline underground storage tanks were removed by Jim Thorpe Oil <br /> of Stockton, California Three additional smaller sand-filled tanks were also discovered and <br /> removed during the removal operation Laboratory analysis of soil samples collected from <br /> beneath the tanks indicate that gasoline was present in soil underlying the 4,000-gallon tank <br /> located at the northwest corner of the site <br /> 1 In December, 1993 Science and Engineering Analysis Corporation (SEACOR) <br /> conducted a subsurface investigation of the property According to the SEACOR report dated <br /> July 22, 1994, fifteen soil borings were completed at the site Three of the borings were <br /> converted to groundwater monitor wells, one was converted to a vapor extraction well, and three <br /> were used as temporary vapor extraction/observation wells The remaining eight borings were <br /> drilled to groundwater where groundwater grab samples and soil samples were collected Based <br /> on the laboratory data generated during their subsurface investigation, SEACOR concluded "the <br /> highest concentrations of contamination are confined mainly to the area directly beneath the site, <br /> and that subsurface contamination, apparently from the site, is present to a lesser degree between <br /> 100 and 200 feet west and southwest of the site " A soil vapor extraction test and an aquifer <br /> 530-001 - 1 LUSH GF-osciENCE <br /> 5 <br />