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C A M B RIA Mr Jeffrey Wong <br /> 0 February 15,2006 ' <br /> i <br /> SB-12 contained up to 1,800 ppm TPHg in soil at 15 fbg Benzene was not detected in soil from <br /> borings SB-11, SB-12, SB-14, SB-15, SB-16, or MW-6 defining it in all directions around the <br /> dispensers MTBE was detected in soil from borings S13-11, SB-12, SB-13,.SB-15, SB-16, and <br /> MW-5 concentrations up to 15 ppm, indicating that impacted soil isP resent in the dispenser enser area � <br /> i <br /> Shallow groundwater data (from wells MW-1 through MW-6) indicate that the highest <br /> Ii <br /> constituent concentrations are present in source area well MW-1 (190 ppb TPHg, 1,700 ppb <br /> MTBE, and 3,700 ppb TBA) Concentrations are significantly lower in owngradient t wells , <br /> MW-5 and MW-6 (maximum concentrations of 85 ppb TPHg, 6 9 ppb MTBE,:and 12 ppb TBA) <br /> Groundwater samples from wells MW-5 and MW- <br /> 6 contained 63 and 7 6 ppb 1,2-DCA, <br /> respectively Prior to this investigation, 1,2-DCA had not been detected at this site Because 1,2- <br /> DCA was not detected in groundwater samples from wells MW-I through MW-4 in previous <br /> sampling events and was not detected in soil from well borings MW-5 or MW-6, Shell believes it <br /> is most likely from an off-site source <br /> Groundwater samples from deeper well MW-7 did not contain detectable concentrations of <br /> TPHg, BTEX, fuel oxygenates, or lead scavengers, delineating these constituents in deeper water <br /> • downgradient of the potential source areas <br /> Shell recommends continued quarterly groundwater monitoring of wells MWA though MW-7 to <br /> establish constituent concentrations and groundwater gradient trends During the next sampling <br /> event, Shell will analyze all wells for 1,2-DCA <br /> g <br /> I <br /> I <br />