2012-04-25_HYDROLOGY - M2002004 - Laserfiche WebLink

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precipitation has been below normal, and the effects of these dry conditions may be resulting in continued elevated TDS and sulfate concentrations in the alluvial groundwater. Radiochemistry During the March 20, 2012 sampling, the Radium 228 activity exceeded the site NPL in well MW -04. As shown in Table 2, prior to this event, radium activities have never exceeded numeric protection levels at the site. The elevated Radium 228 values at well MW -04 appears to be an outlier at this time, as no trend in the radium data has been observed. The combined radium 226 and radium 228 activities do exceed the 5 pCi/L Colorado groundwater Table Value standard in well MW004, as they have for numerous monitoring events. There is no indication that any GCC plant activities are responsible for elevated radium activities at the GCC Facility, as these have been shown to be naturally occurring. Field Parameters Field parameters including temperature, pH, and conductivity were collected during the March 2012 sampling event. Results of the field parameter monitoring are provided in Table 1. The data collected indicate that pH at the site is very close to neutral. Conductivity was generally higher at all wells than it has been historically, and was highest at well MW -03 where the saturated thickness in the well has been as low as 4 inches. Elevated conductivity can be directly correlated to elevated TDS. http: // groundwater. ucdavis .edu /Publications/Harter FWOFS 8084.pdf Quality Control One set of field duplicate samples was collected during the monitoring event. Sample DUP -01 was submitted as a blind field duplicate of primary alluvial well sample MW002. Field duplicate precision is measured as the Relative Percent Difference (RPD) between the primary and duplicate sample results. The RPD is defined as the "absolute value of the difference between the primary and duplicate results, divided by the average of the two results." Precision between the results of the primary and duplicate samples was very good for all parameters tested, with a maximum RPD between field duplicate detections for metals of 1.7 percent for TDS, or agreement within uncertainly windows for the radium 228 comparisons. One equipment rinsate blank was collected during the March 2012 monitoring event, and was submitted for analysis of TDS and sulfate. The blank was collected by pouring laboratory- supplied de- ionized water through a new bailer and into the appropriate sample bottles. No TDS or sulfate were detected in the equipment blank. All laboratory data packages were reviewed to ensure that quality control elements (holding times, blanks, control samples, and matrix spikes), impacting precision and accuracy of the groundwater results presented were within appropriate control limits. Data from the contract laboratories was found to be acceptable in terms of data quality and industry standard presentation. 5