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Mr.Nuel Henderson <br /> Page 3 of 4 <br /> EDB was detected only in MW13B at 160 ppb. 1,2-DCA was detected in wells MW10, <br /> MW 11, MW13B, MW 15A, MW 15B and MW 15C. Detected concentrations of 1,2-DCA <br /> ' ranged from 2.4 ppb (MW15C) to 530 ppb (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 water samples collected from VW4 and VW6 were within <br /> historical ranges. Concentrations in water samples collected from VW2 are the lowest ever <br /> ' recorded. However, an anomalous high water level suggests that this sample may not be <br /> representative of formation water. Gasoline oxygenates were not detected in any of the wells <br /> sampled. The water sample collected from vapor well VW4 contained 1,2-DCA. This <br /> ' additive was not detected in the samples collected from the other two vapor wells sampled. <br /> TPHg and BTEX concentrations are summarized in Table 2. 1,2-DCA,. EDB and gasoline <br /> oxygenate additive concentrations are summarized in Table 3. Attachment B contains <br /> ' laboratory reports and chain of custody documentation. <br /> GROUNDWATER SAMPLING SUMMARY AND DISCUSSION <br /> • Water levels rose during this quarter. Groundwater elevation data continue to show an <br /> easterly groundwater flow direction. Well cluster MW15AlB/C confinues to exhibit an <br /> apparent upward vertical gradient component, while at the MW 16AIB well cluster no <br /> 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 /> ' RECOMMENDATIONS <br /> ' Groundwater Monitoring and Sampling <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 /> ' ' IIGZA_FSIVOLy11DATA1GROUNDZEUt0EK\QMR1200412gm2004.doc <br />