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s NS, .T <br /> Eli <br /> 4n,ta}y(Iraudaat<ar 10ardtnrY9�� <br /> •-- 429 W.KetUeman[ane.Lodi.Cal"Omla <br /> 1.0 INTROD!UCTION <br /> This report presents the results of the second quarterly groundwater monitoring sunnt for <br /> the months of February, March, and April 1991 conducted by Aegis Environ i-nental, Inc. <br /> (Aegis), at the Shell Service Station located at 420 W. Kettleman lane, Lodi, California <br /> (Figure 1). This quarterly monitoring event involved the collection of groundwater <br /> samples, submittal of said samples to a state-certified laboratory for analysis and the <br /> measurement of water levels from the three on site monitoring wells. This report <br /> summarizes the second monitoring evaluation since the installation of the three wells. <br /> 2A SEL1=CTiVE SUMMARlZ4TIOfd OF BACKGROUND INFORMATION <br /> In September 1989,fifteen soil borings were advanced and sampled at the site("Pre-Tank <br /> Replacement Site Assessment Results Report" (Aegis 1989)). The borings ranged in <br /> depth from 11-1h to 21-1h feet below grade (bg). Soil samples collected and analyzed <br /> from one boring along the south edge of the existing underground storage tanks, at 15 <br /> feet bg, reported low concentrations of toluene and total xylenes. Laboratory analysis of <br /> the soil samples for the remaining borings adjacent to the existing dispenser islands and <br /> underground storage tanks indicated total petroleum hydrocarbons as gasoline (TPH as <br /> gasoline), and benzene, toluene, total xylenes, and ethylbenzene (BTEX) were below <br /> detection limits. Low concentrations of toluene were detected at approximately five feet <br /> bg in the northwest quadrant of the site in the location of the formerly proposed 'tank <br /> basin. However, one boring in the northwest quadrant reported TPH as gasoline at 1,060 <br /> ppm at 10 feet bg. The source of the gasoline constituents concentrated in this one soil <br /> - boring has been attributed to a "thief port" present in the existing underground storage <br /> tank system. <br /> Three on site groundwater monitoring wells (Figure 2) were advanced and set in <br /> September 1990, to facilitate groundwater sampling and gradient measurements. The <br /> ground water sample laboratory results reported below detection limit for TPN as <br /> - gasoline, BTEX, organic lead, and ethylene dibromide (EDB) for the three on site wells. <br /> The first quarterly monitoring event included the groundwater sampling for the month of <br /> January 1991. The laboratory ret all wells. bin Iow MW-3, <br /> n limits for TPH as d chloroethane (EDC) was <br /> BTEX, organic lead, and EDB for <br /> reported et 0.0015 parts per million (ppm). <br /> For a complete site history, a description of site conditions, regional and local geology, <br /> hydrology, a description of subsurface conditions, a summarization of analytical results <br /> related to previous investigation and a further definition of the term"thief port"please refer <br /> Report,*dated March 26, <br /> to Aegis'"Site Assessment-Monitoring e5 Bent InstalRelsults ation ReportResults dated October 1989, nd <br /> 1991,"Pre Tank Replacement Site As <br /> "Quarterly Groundwater Monitoring Report," dated April 30, 1991. <br /> a"13C.Wr - <br />