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Quarterly Report - First Quarter 2002 IYAMADA BROTHERS • 15406 South Tracy Boulevard, Stockton, California 1.0. INTRODUCTION IIn accordance with the request of Mr Bob Yamada of Yamada Brothers, Inc , Advanced GeoEnvironmental, Inc (AGE) has prepared this quarterly report for the property located at 15406 South Tracy Boulevard, Stockton, California The scope of work Included quarterly ground water monitoring and preparation of this report The location of the site and the Immediately surrounding area are Illustrated on Figure 1, structures and monitoring well locations on the site are illustrated on Figure 2 20 BACKGROUND AGE has been informed that two USTs were removed from the site in July 1991 Ground water was encountered at a depth of approximately 7 feet below surface grade(bsg) during the UST removal Total petroleum hydrocarbons quantified as diesel (TPH-d) were detected in a grab water sample collected from the excavation at a concentration of 210 micrograms per liter (µg/l) following removal ofthe UST Analytical results of soil samples collected were not available The SanJoaquin County Environmental Health Department(EHD)subsequently required investigation to determine lie the extent of impacted soil and ground water In October 1998, five soil probe borings were advanced at the site for collection of soil and grab ground water samples TPH-d was detected in one soil sample at a concentration of 10 milligrams per kilogram (mg/kg) and In five grab ground water samples at concentations as high as 2,700 µgd Methyl tertiary-butyl ether(MTBE) was detected in four of the five grab ground water samples at concentrations as high as 25 gg/1 No other analytes of concern were detected in the soil and grab ground water samples collected during the October 1998 investigation In November 1999, three ground water monitoring wells were installed at the site Low concentrations of MTBE have been detected in samples collected from the three ground water monitoring wells and a domestic well at the site No other analytes of concern have been detected in ground water samples since monitoring began in November 1999 On 13 April 2001 AGE personnel made a site visit to Identify a potential source for the MTBE contamination, no apparent above-ground source was located In October 2001 four soil robe borings. were advanced at the site for collection of grab ground p g water samples MTBE was detected in the grab ground water sample from boring P-1 at a ' concentration of 2 7 µg/1 The lateral extent of MTBE-impacted ground water was defined to the northwest and east, but has not been defined to the northwest, west or south ' Three domestic wells are located approximately 150 feet southwest of the former USTs location . According to Mr Bob Yamada,bottled water is used for all drinking water and cooking at the site Advanced GeoEnvironmental,Inc