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r <br /> f <br /> CHRONOLOGY <br /> 7-ELEVEN STORE#21756 <br /> 853 E. YOSEMITE AVE., MANTECA <br /> LOP SITE CODE: 1369 <br /> CVRWQCB CASE#39071'1 <br /> APN: 22332015 <br /> 12/09/1998 On this date, three 10,000-gallon underground storage tanks (USTs) were <br /> removed from this site and not replaced. Six soil samples were collected <br /> beneath the USTs and 2 soil samples were collected from beneath the <br /> dispensers located west of the USTs. MTBE was detected in soil samples <br /> collected beneath the USTs. <br /> 06/17/1999 On this date five GeoProbes (GP1-GP5)were completed and samples <br /> were collected for analysis. <br /> 08/13/1999 Date of the Site Assessment Report prepared by IT Corp. which contained <br /> information from the June 1999 investigation. Soil sample GP-4 at 15-16 <br /> feet below ground surface was the only soi=l sample that evidenced <br /> gasoline contamination. Grab water samples were also collected. Only <br /> the water sample from GP-3 contained contaminant concentrations. <br /> 12/20/1999 On this date, three monitoring wells (MW 1-MW3) screened from 10 to 25 <br /> feet were installed on-site. The down-gradient well, MW1, had the <br /> highest ground water contaminant concentrations. Information on the <br /> monitoring well installation is presented in IT Corp. report dated February <br /> 21, 2000. <br /> 4/1-3/2002 On these dates, one additional down-gradient well (MW4) screened from <br /> 15 to 30 feet, two nested vapor extraction/air sparge wells (SP1 — SP2), <br /> and one deep GeoProbe (GP6) to 40 feet were completed. <br /> 04/24/2002 On this date, IT Corp. performed a limited'soil vapor extraction(SVE) <br /> test. <br /> 08/05/2002 Date of IT report Additional Site Assessment and Soil Vapor Extraction <br /> Test on the April 2002 work. The ground water results from the deep <br /> GeoProbe (GP6) and MW-4 were below laboratory detection limits for all <br /> constituents tested. <br /> 10/17/2002 A second SVE test was performed by IT Corp. on this date. Low vapor <br /> concentrations were removed during the tests and the estimated radius of <br /> influence was calculated at 30 feet. This work was documented in the <br /> Fourth Quarter 2002 Monitoring and Sampling Report dated December <br /> 10, 2002. <br />