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I <br /> I <br /> rNESTOGA-ROVERS <br /> &ASSOCIATES <br /> April 9,2009 Reference No.241511 <br /> -2- <br /> GWE System Description <br /> The current GWE system extracts groundwater from wells MW-1 and MW-6,which are the <br /> wells that have historically contained the highest concentrations for 1,2-DCA at the site. <br /> The key components of the interim-GWE system operating at this site include;submersible <br /> pneumatic pumps,an air compressor,air regulators, a ad hoses to route extracted groundwater <br /> to 21,000-gallon water storage tank at the site. The ex xacted groundwater is removed <br /> periodically from the storage tanks by vacuum trucks nd the water is transported to the Shell <br /> Martinez Refinery where it is recycled. This GWE sys em began operation on October 12,2006 <br /> extracting groundwater from well MW-1 only. During April 2008 well MW-6 was added to the <br /> GWE system. <br /> Concentration Trends <br /> 1,2-DCA has primarily been detected in wells MW-1 and MW-6 at this site . The highest <br /> concentration of 1,2-DCA detected in well MW-1 has been 360 micrograms per liter (µg/L) <br /> during October 2005. The highest concentration of 1,2-DCA detected in well MW-6 has been <br /> 50 µg/L during January 2005. Figure 3 was prepared Lo show the concentration of 1,2-DCA <br /> versus time for these two wells. The graph shows a declining concentration trend for both <br /> wells indicating that the GWE system has reduced the concentration of 1,2-DCA in <br /> groundwater beneath the site. <br /> Mass Removal <br /> Operational data collected for this GWE system have been recorded in a mass removal data <br /> table (Table 1). As of February 27,2009,the volume of groundwater pumped by this GWE <br /> system has been 485,971 gallons and the mass of 1,2-DCA removed via GWE has been <br /> 0.0802 pounds. The cumulative mass removed for 1,2 DCA is calculated using the <br /> concentration of 1,2-DCA found in the extraction wells during sampling events and the volume <br /> of groundwater pumped during system operation. <br /> This GWE system has been operating for almost 21/z years and it has not yet removed 0.1 pound <br /> of 1,2-DCA. Based on a removal rate of 0.1 pounds p r 21/2 years,the system would need to <br /> operate for at least 25 years to remove 1 pound of 1,2-DCA. And since the concentration of <br /> 1,2-DCA in the groundwater beneath this site is declitting,the removal rate is also declining <br /> which results in an increase in the time needed to remove a pound of 1,2-DCA. <br /> Worldwide Engineering,Environmental,Construction,and IT Services <br />