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Summary and Analysis of C-Pit and Groundwater Data after Over 4 Years of Monitoring <br />Consistent with the conclusions of the 2007 Report, continued monitoring of C-Pit and the associated well <br />network since 2007 indicates that C-Pit is located in a bedrock system that transmits little if any water flux <br />through the subsurface. However, the fractures in the bedrock units and bedding planes between units do at <br />times, transmit changes in head as the water level in C-Pit rises and falls. Most notably, well CEM-001, which <br />is completed across the Fort Hays Limestone, responds to the head fluctuations from changes in C-Pit water <br />levels. However, well CEM-005 (the dry well), which was completed in the Fort Hays 2,700 feet down dip <br />from CEM-001 at the eastern extent of CEMEX's property, confirmed that this geologic unit does not <br />transmit water. Accordingly, BC has concluded that the Fort Hays Limestone does not meet the definition of <br />an aquifer, and CEMEX therefore proposes to eliminate CEM-001 from future monitoring. <br />Monitoring well CEM-004 was located in the St. Vrain alluvial aquifer immediately northeast and adjacent to <br />the C-Pit bedrock location to monitor for water quality impacts from C-Pit. Monitoring since fall 2007 has <br />not indicated any discernable C-pit impacts to groundwater at this location. CEMEX would like to continue <br />monitoring on a semi annual basis. <br />The attached Table 1 summarizes water quality sampling results for C-Pit, well CEM-001, and well CEM-004 <br />for the four quarters of 2010. All other data collected to date is available in previous DMRS files. <br />Trend Analysis Water Quality Sampling Data <br />The water quality data for C-Pit, CEM-001 (the bedrock well), and CEM-004 (the alluvial well), has been <br />summarized in Figures 1-2 and table 1. The CEM-001 and CEM-004 well water quality data indicates that <br />there are no discernable correlating trends or impacts on water quality at compared to the water in C-pit. <br />Data from 2006 through 2010 for selenium, the key constituent of concern, are depicted on the attached <br />Figures 1 & 2, and the results are summarized below. <br />As demonstrated by the quarterly sampling data and on the attached figures, the filling of C-Pit with inert <br />mine spoil in Spring 2007 significantly lowered both pH and selenium levels in C-Pit water over time, <br />presumably due to sorption by the fill material. Analysis indicates that pH has dropped from over 12 to an <br />average of 8.5 in 2010. In addition, inspection of Figures 1 and 2 confirms that selenium in C-Pit has <br />dropped from over 0.50 mg/l to typically less than 0.10 mg/l during this time period. Most recently <br />selenium averaged 0.09mg/l in 2010 (Table 1). <br />Figure 1 shows that selenium concentrations in CEM-001 have been consistently low relative to C-Pit or <br />below detection, with an outlier in September 2009 as high as 0.12 mg/1. Most recently in December 2010, <br />selenium was measured at 0.0031 mg/l drastically lower than the highest measurements in 2009. All of the <br />quarterly measures for 2010 indicate that selenium averaged.027 mg/1 in well CEM-001. <br />Selenium levels in CEM-004 occur at very low levels, two orders of magnitude below C-Pit levels, and often <br />below levels of detection (Figure 2). Additionally, inspection of the trends for other analytes at CEM-004 <br />does not indicate any impacts from C-Pit water at this location (Table 1). <br />No correlation or trend is observed between C-Pit and CEM-001 chloride data. Chloride concentrations in <br />CEM-001 are already higher than those reported in C-Pit, and therefore the chloride data cannot help <br />determine whether or not there is transport through the limestone. Although it is true that past data indicate <br />that the limestone formation at CEM-001 is influenced by C-Pit based on measured heads at both locations, <br />it is believed that this connection is from fracturing in the shale units, fractures in the limestone, and along <br />the bedding planes between units, or some combination. As previously discussed, the lack of water in former <br />compliance well CEM-005 confirmed that the Fort Hays Limestone is not transmitting water, and therefore is <br />not an aquifer. <br />2