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<br /> 5. SUMMARY
<br /> iBetween 20 and 22 September 2004, ETIC observed the drilling of one exploratory soil boring
<br /> (EBI) and the installation of three nested injection point pairs (IP1A, IP1B, IP2A, IP2B, and
<br /> IP3A, IP313) at former Exxon Retail Site 7-3942, located at 4444 North Pershing Avenue,
<br /> Stockton, California
<br /> Soils encountered during the drilling of the borings were generally consistent with those
<br /> i observed in previous bonngs at the site Soils encountered in the borings consisted primarily of
<br /> sandy silt, clayey silt, and silty sand down to 62 feet bgs,the total depth explored
<br /> iThirty-four soil samples from the borings were collected and analyzed for TPH-g, BTEX, and
<br /> MTBE Two of the soil samples were also analyzed for DIPE, TBA, TAME, EDB, ETBE, and
<br /> 1,2-DCA TPH-g and benzene were detected at maximum concentrations of 5,920 mg/kg (IPI,
<br /> 35-35 5 feet bgs) and 5 73 mg/kg (21, 31-31 5 feet bgs), respectively MTBE was not detected
<br /> above laboratory reporting limits in any of the soil samples TPH-g and BTEX were not detected
<br /> in any samples collected at or above 21.5 feet bgs
<br /> Exploratory boring EBI was drilled immediately downgradient of the source area Analytical
<br />' results for the deepest sample from EB 1, collected at a depth interval of 615 to 62 feet bgs, were
<br /> 4 99 mg/kg for TPH-g and 0 0172 mg/kg for benzene, and the sample did not contain MTBE
<br /> above the laboratory reporting limit In the three samples (46-46 5, 51 5-52, and 57 5-58 feet
<br /> lie bgs) collected above this bottom sample (61 5-62 feet bgs), TPH-g was not detected above the
<br /> laboratory reporting limit Based on these analytical results, the vertical extent of hydrocarbon
<br /> impacted soil appears to be delineated
<br /> Groundwater samples were collected from injection points IP1A, 1P1B, IP2A, IP2B, and IP313
<br /> on 28 September 2004 The samples were analyzed for TPH-g, BTEX, and MTBE TPH-g,
<br /> i ethylbenzene, and xylenes were detected at maximum concentrations of 94,100 ug/L, 3,270
<br /> ug/L, and 15,200 ug/L, respectively, in injection point IP2B Benzene and toluene were detected
<br /> at maximum concentrations of 5,470 ug/L and 18,800 ug/L, in injection point IP 1 B MTBE was
<br /> not detected in any of the groundwater samples at or above the laboratory reporting limit
<br /> The concentrations of TPH-g and BTEX were of similar magnitude in both the potential
<br /> hydrogen peroxide points and the potential ozone points, as the point pairs are screened across
<br /> similar lithologies and only separated by 3 to 4 5 feet It is proposed that only the potential
<br /> ozone points be incorporated into the quarterly groundwater monitoring program for the site If
<br /> the SJCEHD concurs, then only injection points IPIB, IP2B, and IP3B will be incorporated into
<br /> the quarterly groundwater monitoring program for the site
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<br />' G 1PM)CCU\73942VMASTERI WPUPR I204\IFRtext doc l 1
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