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amec�9 <br /> 3.4.3 Other COCs Detected in Groundwater Samples <br /> Other compounds were detected in depth-discrete groundwater samples collected by <br /> Geomatrix in 2005, but at substantially lower concentrations than TCE. These include PCE, <br /> cDCE, 1,1-dichloroethane (1,1-DCA), 1,1-dichloroethene (1,1-DCE), vinyl chloride, and <br /> chloroform. Concentrations of 1,1-DCA ranging from 1.1 to 96 pg/L, 1,1-DCE ranging from <br /> 0.73 to 64 pg/L, and chloroform ranging from 0.51 to 70 pg/L were detected in samples <br /> collected from the eastern portion of the Site at CPT-1, CPT-11, CPT-12, CPT-13, CPT-15, <br /> and CPT-18. Historically, these constituents have been detected in groundwater samples from <br /> wells M-2A and M-213. These wells are located near the eastern portion of the Site in the <br /> vicinity of the railroad tracks where small volumes of chloroform and 1,1,1-TCA may have <br /> been released to the ground surface (RUST, 1994a). Vinyl chloride was reported as detected <br /> in two of the 54 samples collected by Geomatrix, at concentrations of 0.73 and 1.6 pg/L at <br /> depths of 102 and 112 feet bgs. PCE was reported in two samples (4.3 and 6.1 pg/L) and <br /> cDCE concentrations were generally less than 5 pg/L except for three samples (20, 24 and <br /> 26 pg/L from depths between approximately 90 and 103 feet bgs). <br /> 3.4.4 Mass Recovery by Groundwater Extraction Wells <br /> Recent mass removal rates by Nestle's Lower A-zone groundwater extraction wells ranged <br /> from approximately 0.02 to 0.3 lbs/day in 2007 and 2008, with the greatest mass removal <br /> occurring at EI-1, while it was pumping at rate of approximately 142.5 gpm (Table 3). The <br /> concentration of TCE decreased from 150 pg/L to 89 pg/L between February 2007 and 2008 <br /> in groundwater samples from EI-1, when pumping decreased from 142.5 to 88 gpm over this <br /> same time period. This scenario would not be expected if a source for TCE were near EI-1, <br /> where under such circumstances, TCE concentrations would increase with decreased <br /> pumping because of less dilution with "clean" groundwater. The results of the 2005 Geomatrix <br /> CPT and groundwater characterization program suggest that higher concentrations of TCE are <br /> present in Middle and Lower A-zone groundwater west of the Site, rather than beneath the <br /> Site. It is possible that no substantial TCE source is present near EI-1 and EW-1, where mass <br /> removal rates calculated in Table 3 reflect high pumping rates and the capture of a relatively <br /> widespread, but dilute TCE plume. <br /> Initial mass removal rates reported during IRAP pumping were estimated to be as high as <br /> approximately 0.23 lbs/day, but have since declined to approximately 0.03 lbs/day (EU-3) and <br /> 0.05 lbs/day (EU-4). This rapid decline in mass removal rates is an indication that the <br /> extraction wells were initially surrounded by TCE-affected groundwater, but later began to <br /> capture groundwater with lower TCE concentrations, perhaps even clean groundwater. The <br /> relatively rapid decline and subsequent stabilization in mass removal rates may also reflect the <br /> formation of a hydraulic stagnation zone between pumping wells EU-3 and EU-4. This zone <br /> may have formed within the area of relatively high Upper A-zone TCE concentrations, greatly <br /> AMEC Geomatrix, Inc. <br /> I:\Doc_Safe\9000s\9837.005\4000 REGULATORY\SCM_01.30.09\1_text\SCM Report Final.doc 21 <br />