2012-08-07_HYDROLOGY - M2002004 - Laserfiche WebLink

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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. CONCLUSIONS Results of the second quarter 2012 groundwater sampling performed at the GCC Rio Grande Cement Plant during June 2012 are presented herein. All analyses required were performed as requested. The Colorado DRMS has provided NPL standards for the GCC groundwater monitoring project for four constituents of concern (sulfate, TDS, Radium 226 and Radium 228). The Sulfate and TDS numeric standards were exceeded during this sampling event at well MW -03 only. The radium 228 exceedence from the previous sampling event (March 2012) was considered to be an isolated event, and this was verified by the results of the June 2012 event. The sulfate exceedence at MW -03 was the first noted for the project. The concentration for TDS at MW -03 marks the third consecutive event where TDS has exceeded NPLs. Upward ' concentration trends for both TDS and Sulfate at wells MW -02 and MW -04 were reversed. However, due to the increasing TDS at MW -03, GCC will continue to sample target constituents on a quarterly basis to determine if the trend continues. Given that well MW -03 appeared to be most impacted by the dry conditions noted during 2011, chemistry at this well may be slowest to recover to historically normal levels. GCC believes that elevated TDS concentrations are likely related to falling water levels in the vicinity of the St Charles River compliance wells, and subsequent concentration of dissolved constituents in the shallow aquifer. These dry conditions at the facility also minimize the potential for any groundwater to reach the compliance wells from the cement plant, as continuous saturated conditions between the plant and the compliance wells are unlikely to exist (as shown by well MW -05) when water levels drop. 6