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The combined radium 226 and 228 activity has exceeded the 5 pCi/L Colorado <br />groundwater standard in wells MW002 and MW004 for at least the last four monitoring <br />events. Radium activity exceeded the standard in well MW003 in April 2010. <br />Radiochemistry activities exceeding groundwater standard are shown as shaded cells in <br />Table 1. <br />There is no indication that any plant activities are responsible for elevated radiochemistry <br />activities at the GCC Facility. Elevated radionuclide activities in Colorado aquifers are <br />generally associated with leaching from granitic bedrock masses that underlay many <br />aquifers in the state. The Dakota formation in the Denver basin, which extends from <br />Pueblo to Wyoming, is also host to minor Uranium roll front deposits. These deposits form <br />when groundwater containing dissolved uranium comes into contact with reducing <br />conditions, causing precipitation of the Uranium. Such naturally occurring conditions are <br />the likely cause of the elevated gross alpha activities in the Dakota aquifer beneath the GCC <br />Facility. <br />Field Parameters <br />Field parameters including temperature, pH, and conductivity were collected during the <br />April 2011 sampling event. Results of the field parameter monitoring are provided in Table <br />1. The data collected indicate that pH at the site is very close to neutral. Conductivity is <br />highest in the alluvial wells where some turbidity was noted. <br />Colorado Division of Reclamation Mining an Safety Parameters <br />The Colorado Division of Reclamation Mining and Safety (DRMS) sent a letter to GCC <br />dated December 8, 2009. The letter presented numeric standards for groundwater <br />monitoring for four parameters (TDS, Sulfate, Radium 226, and Radium 228). DRMS <br />generally selected the historic maximum concentration prior to May 2009 as the numeric <br />standard for each of the four parameters. Table 1 lists the DRMS standards for the four <br />constituents of concern in the footnotes. None of the concentrations for the four <br />constituents of concern exceed the DRMS standards for the first half 2011 monitoring <br />event. <br />Quality Control <br />One set of field duplicate samples was collected during the monitoring event. Sample <br />DUP -01 was submitted as a blind field duplicate of primary alluvial well sample MW002. <br />Field duplicate precision is measured as the Relative percent difference (RPD) between the <br />primary and duplicate sample results. The RPD is defined as the "absolute value of the <br />difference between the primary and duplicate results, divided by the average of the two <br />results." Precision between the results of the primary and duplicate samples was very good <br />4 <br />