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" Mr Nuel Henderson <br /> Page 3 of 4 <br /> MTBE was not detected in wells MW8, MW13B, MW 15C and MW 17C MTBE was detected <br /> in wells MW1 (17 ppb), MW7 (4 5 ppb), MW11 (93 ppb), MW15A (15 ppb), and MW15B <br /> (1,000 ppb) These wells are affected by MTBE releases originating at 101 S Wilson Way <br /> and/or 130 S Wilson Way <br /> EDB was detected only in monitoring well MW13B, at a concentration of 280 ppb 1,2-DCA <br /> was detected in each of the sampled wells, except MW7 and MW17C Concentrations of 1,2- <br /> DCA ranged from S 3 ppb in MW8 to 2,300 ppb in MW13B Analytical results for gasoline <br /> oxygenates, EDB and 1,2-DCA are summarized in Table 3 Attachment B contains laboratory <br /> reports and chain 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 VWI The water sample collected from <br /> vapor well VW1 contained 1,2-DCA at a concentration of 1,100 ppb and EDB at a <br /> concentration of 270 ppb TPHg and BTEX concentrations are summarized in Table 2 1,2- <br /> DCA, EDB and gasoline oxygenate additive concentrations are summarized in Table 3 <br /> Attachment B contains laboratory reports and chain of custody documentation <br /> GROUNDWATER SAMPLING SUMMARY AND (DISCUSSION <br /> o Water levels rose during this quarter Groundwater elevation data continue to show a <br /> predominantly easterly groundwater flow direction <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 /> a The plume of contamination originating from offsite source(s) is continuing to spread <br /> MTBE has affected downgradient wells MW 11, MW 15A and MW 15B Detectable levels <br /> of MTBE and 1,2-DCA have been recorded in upgradient well MW1 during the last five <br /> sampling events This may indicate further encroachment of the plume of contamination <br /> originating at 101 S Wilson Way <br /> The third quarter groundwater sampling event was conducted during August Preliminary <br /> laboratory data from the third quarter event indicate some significant changes in contaminant <br /> levels and distribution have occurred <br /> A Site Conceptual Model was intended to be part of this report However, we feel the third <br /> quarter data are pertinent to the model and the SCM will be included in the third quarter <br /> groundwater sampling report <br /> G IGROUNDZEROEKIQMR1200612gm2006 doc <br />