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C A M B R A Mr Jeffrey Wong <br /> February 15, 2006 <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, S13-14, SB-15, SB-16, or MW-6 defining it in all directions around the <br /> dispensers MTBE was detected in soil from borings SB-11, SB-12, S13-13, S13-15, SB-16, and <br /> MW-5 concentrations up to 15 ppm, indicating that impacted soil is present in the dispenser area <br /> Shallow groundwater data (from wells MW-1 through MW-6) indicate that the highest <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 downgradient 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-6 contained 63 and 7 6 ppb I,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 MW-1 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 /> 8 <br />