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' Mr.Nuel Henderson <br /> Page 3 of 4 <br /> ' EDB was not detected in any of the wells sampled. 1,2-DCA was detected in wells MW2, <br /> MWS, MW8, MW9, MW12, MW1313, MW15A, MW15B and MW15C. Detected <br /> ' concentrations of 1,2-DCA ranged from 2.3 ppb (MW8) to 1,200 ppb (MW13B). Analytical <br /> results for gasoline oxygenates, EDB and 1,2-DCA are summarized in Table 3. Attachment B <br /> contains laboratory reports and chain of custody documentation. <br /> Vapor Extraction Wells <br /> TPHg and BTEX concentrations in water samples collected from VW1 and VW3 were within <br /> historical ranges. MTBE was detected in VW3 for the first time, at a concentration of 55 ppb. <br /> The water sample collected from vapor well VW1 contained 1,2-DCA at a concentration of <br /> 1,700 ppb. This additive was not detected in the sample collected from VW3. TPHg and <br /> BTEX concentrations are summarized in Table 2. 1,2-DCA, EDB and gasoline oxygenate <br /> ' additive concentrations are summarized in Table 3. Attachment B contains laboratory reports <br /> and chain of custody documentation. <br /> GROUNDWATER SAMPLING SUMMARY AND DISCUSSION <br /> ' • Water levels fell during this quarter. Groundwater elevation data continue to show an <br /> easterly-northeasterly groundwater flow direction. Well cluster MW15A/B/C continues to <br /> , . exhibit an apparent upward vertical gradient component, while at the MW16A/B well <br /> cluster a downward vertical gradient component was observed during this event. <br /> • 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 the concentrations are stable to decreasing. <br /> ' • The plume of contamination originating from offsite source(s) is continuing to spread. <br /> High levels of MTBE persist in wells along the southern portion of the property. <br /> 1 <br /> RECOMMENDATIONS <br /> ' Groundwater Monitoringand Sampling <br /> P g <br /> Reduce the sampling frequency for wells that are monitoring the plume of contamination <br /> originating from the onsite release. Given the massive quantity of historical groundwater <br /> ' monitoring and chemical analysis data at this site, quarterly monitoring and sampling for this <br /> site is not warranted. Transfer ownership or sampling responsibility for the wells that are <br /> affected by the offsite release(s) to the appropriate responsible parties. <br /> ' 11GZA FSIVOL-11DATAIGROUNDZFaOEKIQMR120040gtn2004,doc <br />