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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 />Precision between the results of the primary and duplicate samples was very good for all <br />parameters tested. <br />Due to very windy conditions at the time of sampling, a field blank was collected to <br />evaluate the potential for sample contamination due to ambient conditions (i.e., dust <br />contacting sample containers and equipment during sample collection). Arsenic was <br />detected in the field blank at a concentration similar to those of the groundwater samples. <br />Arsenic detections in groundwater may be the result of blank contamination bias, and are <br />evaluated as false positive results. <br />All laboratory data packages were reviewed to ensure that quality control elements <br />(holding times, blanks, control samples, and matrix spikes), impacting precision and <br />accuracy of the groundwater results presented were within appropriate control limits. <br />Data from the contract laboratories was found to be acceptable in terms of data quality <br />and industry standard presentation, with the following considerations. A project specific <br />matrix spike analysis was performed on sample MW004. Matrix spike recoveries for <br />' silver were slightly low. Silver was not detected in any samples. Any low bias to the <br />silver results is likely to be very small. Matrix spike recoveries for barium were <br />significantly low at 49 percent. Barium was detected in all samples. These detections <br />t could be biased low and should be considered as estimated values. <br />CONCLUSIONS <br />Results of the Second Half, 2008 groundwater sampling performed at the GCC Rio <br />' Grande site during November, 2008 are presented herein. All analyses required were <br />performed as requested. <br />Results for several dissolved metals were found to be non-detect for all wells. These <br />metals were also reported as non-detect in the first and second quarterly events. If these <br />constituents continue to be non-detected in future samplings events, or if these have not <br />been historically detected, GCC Rio Grande may petition to have these constituents <br />removed from the routine monitoring program. <br />' Selenium was the only metal to exceed a primary drinking water standard. This occurred <br />at well MW004. Selenium has exceeded the drinking water standard at well MWO04 for <br />each of the three monitoring events performed in 2008. Elevated selenium in the vicinity <br />1 of the St. Charles River and other areas is documented to be naturally occurring with <br />sources in units of the Pierre Shale, the Niobrara Formation and from soils formed from <br />