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have followed dry summers with little fall precipitation. Low groundwater levels may tend <br />to concentrate dissolved chemical species, raising the level of TDS. GCC anticipates that <br />TDS levels will again decrease in the spring event, assuming winter precipitation raises <br />water levels such that the St. Charles River regains flow. <br />Radiochemistry <br />As shown in Table 1, radium 226 and radium 228 concentrations were well below the <br />DRMS Numeric Protection Levels in the October 2011, semi annual sampling event. As <br />shown in table 2, radium activities have never exceeded numeric protection levels at the <br />site. The combined radium 226 and 228 activity does exceed the 5 pCi/L Colorado <br />groundwater Table Value standard in well MW004, as it has for numerous monitoring <br />events. There is no indication that any GCC plant activities are responsible for elevated <br />radium activities at the GCC Facility, as these have been shown to be naturally occurring. <br />Field Parameters <br />Field parameters including temperature, pH, and conductivity were collected during the <br />October 2011 semi annual sampling event. Results of the field parameter monitoring are <br />provided in Table 1. The data collected indicate that pH at the site is very close to neutral. <br />Conductivity was generally higher at all wells than it has been historically, and was highest <br />at well MW -03 where the saturated thickness in the well was only 4 inches. Elevated <br />conductivity can be directly correlated to elevated TDS. <br />http: // groundwater .ucdavis.edu /Publications/Harter FWQFS 8084.pdf <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 />for all parameters tested, with a maximum RPD between field duplicate detections for <br />metals of 1.1 percent for TDS, or agreement within uncertainly windows for the radium 228 <br />comparisons. <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 />All laboratory data packages were reviewed to ensure that quality control elements (holding <br />times, blanks, control samples, and matrix spikes), impacting precision and accuracy of the <br />groundwater results presented were within appropriate control limits. Data from the <br />contract laboratories was found to be acceptable in terms of data quality and industry <br />standard presentation. <br />5 <br />