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May 24, 1996 Quarterly Monitoring Report <br /> Chapin Brothers Automobile Repair Facility Stockton, California <br /> 1.0 INTRODUCTION a <br /> This report summarizes the analytical results generated during a quarterly groundwater <br /> monitoring event conducted by Lush Geosciences at the Chapin Brothers Automobile Repair site <br /> located at 1766 Monte Diablo Avenue in Stockton, California. The property is located on the <br /> southeast corner of the intersection of Monte Diablo Avenue and Buena Vista Avenue in the City <br /> of Stockton, California(Figure 1). A service station operated on the property from the late 1930s <br /> 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 /> M <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 /> In December 1993 Science and Engineering Analysis Corporation (SEACOR) conducted <br /> a subsurface investigation of the property. According to the SEACOR report dated July 22, <br /> 1994, fifteen soil borings were completed at the site. Three of the borings were converted to <br /> groundwater monitor wells, one was converted to a vapor extraction well, and three were used as <br /> temporary vapor extraction/observation',wells. The remaining eight borings were drilled to <br /> groundwater where groundwater grab samples and soil samples were collected. Based on the <br /> laboratory data generated during their subsurface investigation, SEACOR concluded "the highest <br /> concentrations of contamination are confined mainly to the area directly beneath the site, and that <br /> subsurface contamination, apparently from the site, is present to a lesser degree between 100 and <br /> 200 feet west and southwest of the site.' A soil vapor extraction test and a aquifer pump test <br /> 530-001 '' - 1 - <br /> LUSH GEoscll;NcEs <br />