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r <br /> I <br /> r <br /> ' Mr Nuel Henderson <br /> Page 3 of 4 <br /> • Vapor Extraction Wells <br /> Petroleum hydrocarbon concentrations in the sampled vapor wells were within historical ranges <br /> Gasoline oxygenate additives, and EDB were not detected in wells VW4 and VW6 1,2-DCA was <br /> reported in well VW4 at a concentration of 75 ppb, but was not found in well VW6 TPHg and <br /> BTEX 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 chain of <br /> custody documentation <br /> GROUNDWATER SAMPLING SUMMARY AND DISCUSSION <br /> • Water levels rose during this quarter Groundwater elevation data continue to show an easterly <br /> groundwater flow direction Well cluster MW 15AIB/C continues to exhibit an upward vertical <br /> gradient component, while at the MW 16AIB well cluster the vertical gradient continues to be <br /> downward <br /> • Petroleum hydrocarbon concentrations in the wells affected by the onsite release were within <br /> historical ranges The extent of groundwater contamination associated with the onsite release is <br /> stable, and the concentrations are stable to decreasing <br /> • The plume of contamination originating from Top Filling Station is continuing to spread High <br /> levels of MTBE persist in wells MW3, MW4, MW 11 and MW 14, which are located along the <br /> southern portion of the property Moreover, the concentrations of MTBE in downgradient well <br /> MW15B appear to be increasing The ever-increasing concentrations of MTBE in the southerly <br /> wells (most notably MW 14) and well MW 15B attests to plume mobility <br /> VAPOR EXTRACTION SYSTEM ACTIVITIES <br /> Vapor Extraction System Operation <br /> The soil vapor extraction system was not operated during the second quarter of 2003 <br /> RECOMMENDATIONS <br /> Groundwater Monitoring and Sampling <br /> Reduce the monitoring and sampling frequency to a semi-annual schedule Given the massive quantity <br /> of historical groundwater monitoring and chemical analysis data at this site, quarterly monitoring and <br /> sampling for this site is not warranted <br /> G IGR0UNDZEIR0MQMRU00352gm2003 doe <br /> 4 <br />