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for all parameters tested, with a maximum RPD between field duplicate detections for <br />metals of 24 percent for selenium. The maximum RPD between field duplicate detections <br />for general chemistry parameters was 30 percent for alkalinity. <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, with the following considerations. Matrix spike recoveries for <br />manganese, chromium, and iron were high in batch spikes. Dissolved chromium and iron <br />were not detected in the associated samples, and no action is required. The high matrix <br />spike recovery for manganese indicates that sample results for manganese may be biased <br />slightly high. Spike recoveries for zinc are not assessed, as the zinc concentration in the <br />sample spiked was more than four times higher than the spike added amount. <br />Alkalinity, chloride, and sulfate were detected in low concentration in the general chemistry <br />method blanks. No action is taken, as these parameters were detected in the associated <br />samples at concentration orders of magnitude greater than the blank detections. Precision <br />and accuracy, as demonstrated by the results of the laboratory quality control analyses is <br />determined to be acceptable. <br />CONCLUSIONS <br />Results of the first half, 2011, groundwater sampling performed at the GCC Rio Grande <br />Cement Plant during April 2011 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 metals <br />include: aluminum, beryllium, chromium, cobalt, nickel, iron, silver, vanadium, zinc, <br />antimony, arsenic, cadmium, lead, thallium, and mercury. Most of these metals have also <br />been reported as non - detect in the previous quarterly sampling events. If these constituents <br />continue to be non - detected in future samplings events, or if these have not been <br />historically detected, GCC Rio Grande may petition to have these constituents removed <br />from the routine monitoring program. <br />Selenium was the only metal to exceed a primary drinking water standard. This occurred at <br />well MW004. Selenium has exceeded the drinking water standard at well MW004 for each <br />of the monitoring events performed at the site to date. Elevated selenium in the vicinity of <br />5 <br />