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The combined radium 226 and 228 activity exceeded the 5 pCi/L Colorado groundwater <br />standard in wells MW003. Radium activity has exceeded the standard in well MW004 for <br />several of the previous monitoring events. Radiochemistry activities exceeding <br />groundwater standard are shown as shaded cells in 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 />October 2010 sampling event. The data collected indicate that pH at the site is very close to <br />neutral. Conductivity is highest in the alluvial wells where some turbidity was noted. <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 (PRD) 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 />for all parameters tested, with the following exception. Precision for the copper duplicate <br />results is poor, with an RPD of 144 percent. The copper detection of 25.9 microgram per <br />liter (ug/L) in sample MW002 appears to be anomalous, as copper has not been detected in <br />this well in previous monitoring events. <br />One equipment rinsate blank was collected during the monitoring event. The blank was <br />collected by pouring laboratory-supplied de-ionized water through a new bailer and into the <br />appropriate sample bottles. No target constituents were detected in the equipment blank, <br />with one exception. Thallium was detected in the equipment blank at a concentration of <br />0.78 ug/L. Thallium was not detected in any of the associated groundwater samples, and no <br />bias to the sample results is indicated. <br />All laboratory data packages were reviewed to ensure that quality control elements (holding <br />4