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Mr Nuel Henderson <br /> Page 3 of 4 <br /> MTBE was not detected in wells MW8, MW13B and MW15C MTBE was detected in wells <br /> MWl (12 ppb), MW7 (1 7 ppb), MW11 (91 ppb), MW12 (520 ppb), MW15A (10 ppb), and <br /> MW 15B (10 ppb) These wells are affected by MTBE releases originating at 101 S Wilson <br /> Way and/or 130 S Wilbon Way <br /> EDB was not detected in any of the wells sampled 1,2-DCA was detected in each of the <br /> sampled wells, except MW7, MW8 and MW15B Concentrations of 1,2-DCA ranged from <br /> 7 6 ppb in MW 11 to 2,000 ppb in MW 13B Analytical results for gasoline oxygenates, EDB <br /> and 1,2-DCA are summarized in Table 3 Attachment B contains laboratory reports and chain <br /> of custody documentation <br /> Vapor Extraction Wells <br /> TPHg and BTEX concentrations in the water sample collected from VW1 were within <br /> historical ranges MTBE was not detected in well VW1 The water sample collected from <br /> vapor well VW1 contained 1,2-DCA at a concentration of 830 ppb TPHg and BTEX <br /> concentrations are summarized in Table 2 1,2-DCA, EDB and gasoline oxygenate additive <br /> concentrations are summarized in Table 3 Attachment B contains laboratory reports and <br /> chain of custody documentation <br /> GROUNDWATER SAMPLING SUMMARY AND IDESCUSSION <br /> o Water levels rose during this quarter Groundwater elevation data continue to show a <br /> predominantly easterly groundwater flow direction An upward vertical gradient <br /> component was observed across the site <br /> o Petroleum hydrocarbon concentrations in the wells affected by the onsite release were <br /> within historical ranges The extent of groundwater contamination associated with the <br /> onsite release is stable and contaminant concentrations are stable to decreasing <br /> o The plume of contamination originating from offsite source(s) is continuing to spread <br /> MTBE has affected downgradient wells MW 11, MW 12, and MW 15B The concentration <br /> of MTBE detected in MW 12 during this event was the highest ever recorded in that well <br /> Detectable levels of MTBE and 1,2-DCA have been recorded in upgradient well MW1 <br /> during the last four sampling events This may indicate further encroachment of the plume <br /> of contamination originating at 101 S Wilson Way <br /> UPDATE ON SECOND QUARTER ACTIVITIES <br /> Deep monitoring well MW 17C was installed at the site between April 20 and 25 and has been <br /> developed and sampled Second quarter groundwater sampling was completed on June 8 <br /> G1GROlJN1)ZmR0EKIQMR12006Ugm2006 doc <br />