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May 29, 2013 <br />//CC-MC-X <br />At this time, CEMEX has not been able to find an obvious explanation for the anomaly in the <br />February 2013 data. The potential sources of the apparent short-term increase in chloride and <br />sulfate considered by CEMEX include: <br />Fertilization. CEMEX checked with adjacent property leasee and no fertilization had <br />taken place since the previous spring in the area surrounding CEM -004. <br />Seepage from C Pit. As noted in the Technical Revision No. 8, on page 4 -2, Figure 5, <br />and Figure 10, there does not appear to be a direct hydrogeologic connection between C- <br />Pit and CEM -004 that would explain rapid chemical impacts to the water monitored in <br />CEM -004. CEM -004 is in the alluvium, which is separated from C -Pit by the Smokey <br />Hill Shale. Therefore, it is expected that if there was any impact to the groundwater in <br />CEM -004 from C -Pit, this would be a very slow and gradual change (if any) and not a <br />rapid fluctuation as was observed over a couple of weeks. To continue to improve our <br />understanding of any potential hydrogeologic connection between C -Pit and CEM -004, <br />CEMEX will continue to conduct quarterly monitoring for cations and anions to monitor <br />the chemical signature of the water from these two areas for the next year. After a year <br />CEMEX would like to reevaluate whether this monitoring regime should be continued. <br />• Influence from the Highland Irrigation Ditch that feeds the Foothills Reservoir. While <br />the irrigation ditch runs periodically, it was not known to be running in February 2013. <br />CEMEX will attempt to obtain ditch information and flow schedules from the ditch rider. <br />• Mineral weathering /dissolution of minerals. It is not clear if there is a change in mineral <br />composition due to weathering (dissolution) that may be impacting the CEM -004 <br />groundwater. Rapid fluctuations in the chloride and sulfate concentrations are typically <br />uncommon. However, as mentioned above, CEMEX will continue to conduct quarterly <br />monitoring to identify any potential trends. <br />Conclusion and Recommendations <br />CEMEX will continue to conduct quarterly monitor for the full set of cations and anions, as <br />previously discussed, plot trends using Stiff diagrams, and watch for any changes in the CEM - <br />004 chemical signature or any indication of potential impact from C -pit. This information will <br />be provided in the quarterly reports. <br />Should you wish to discuss further, please let me know what time is most convenient for you. If <br />there are any questions regarding the above information please contact me at (303) 823 -2115. <br />Sincerely, <br />Dense Arthur, Ph.D. <br />Environmental Manager <br />5134 Ute Hwy PO Box 529 <br />Lyons, CO 80540 <br />4 <br />