2012-11-14_HYDROLOGY - M2002004 - Laserfiche WebLink

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have followed dry summers with little fall precipitation. Low groundwater levels may tend to concentrate dissolved chemical species, raising the level of TDS. GCC expected to see TDS concentrations decrease in the current spring and early summer sampling events. However, winter precipitation has been below normal, with Colorado experiencing an extended drought, and the effects of these dry conditions may be resulting in continued elevated TDS and sulfate concentrations in the alluvial groundwater. Field Parameters Field parameters including temperature, pH, and conductivity were collected during the September 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 continues to be elevated at well MW -04. Elevated conductivity can be directly correlated to elevated TDS. http: // groundwater .ucdavis.edu /Publications/Harter FWQFS 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 MW -02. 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 TDS results is very good for the duplicate pair. One equipment rinsate blank was collected during the September 26, 2012 monitoring event for analysis of TDS. The blank was collected by pouring laboratory- supplied de- ionized water through a new bailer and into the appropriate sample bottles. TDS was detected in the equipment blank at the reporting limit of 10 mg/L. This concentration is orders of magnitude less than the TDS detections in the groundwater samples, and no bias to the sample results is indicated. CONCLUSIONS Results of the third quarter 2012 groundwater sampling performed at the GCC Rio Grande Cement Plant during September 2012 are presented herein. Samples were submitted for analysis of TDS only. TDS concentrations at MW -03 have exceeded NPLs in three consecutive events leading up to the current event. Steadily declining water levels have been observed in all wells, as the St. Charles River has gone dry. MW -03 was dry, and no sample was collected. The TDS concentration at well MW -04 slightly exceeded the NPL. TDS concentrations at MW -04 have fluctuated around the NPL, but no trend is apparent. 4