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AAMMA <br />To conclude, for the reasons outlined in the 2007 report and in subsequent quarterly reports since 2007, <br />CEMEX continues to believe that that the primary source of inflow into C-Pit is seepage from the Boulder <br />Feeder Canal, likely at multiple locations, and varying seasonally depending upon the Canal flow rate at any <br />given time. This conclusion is supported by the continuing observed saturated conditions along the reach of <br />the Canal founded on fill southeast of C-Pit. Water leaking from the Canal in this reach makes its way along <br />ditches to a 54-inch culvert under the Canal that in turn discharges to the pond located between the Canal <br />and the southwestern corner of C-Pit. Seepage losses from that pond would travel along the top of the shale <br />formation that makes up the floor of C-Pit, eventually reaching the pit, which is the low point in the system. <br />The preceding conclusion is also supported by the continuing observation of seepage entering C-Pit from its <br />western highwall, which CEMEX believes is evidence of saturated mine spoil on the west side of the un- <br />mined block that makes up the highwall. Seepage rates out of the highwall are observed to vary seasonally <br />with the use of the Boulder Feeder Canal, increasing in summer fall, and dropping off during the non- <br />irrigation season. This seepage zone was observed during the DRMS inspection of December 3, 2010. <br />CEMEX continues to have discussions with the owner of the Boulder Feeder Canal to determine our options <br />to reduce the inflows into C-Pit. CEMEX will keep DRMS apprised of further developments as they occur. <br />Proposed Monitoring Plan Going Forward (TR 11) <br />As discussed in our meeting with DMRS, CEMEX proposes to continue monitoring C-Pit water and alluvial <br />well CEM-004 for TDS and pH, on a semi-annual basis, starting in this first half of 2011. The results of this <br />monitoring will be discussed and reported to DRMS in semi-annual reports. If the monitoring determines <br />that C-Pit water may be impacting the St. Vrain alluvium, DRMS will be consulted to determine the <br />appropriate response. <br />CEMEX will also continue to monitor the elevation of C-Pit water in the remaining north end pond on a <br />regular basis. Additionally, C-Pit water levels will be reduced as the water is used for process cooling <br />whenever possible. <br />C-Pit Closure <br />CEMEX at this time has no plans to permanently close C-pit. C-Pit continues to be the permitted disposal <br />area for CKD produced by the Lyons plant. CEMEX does commit to keeping the volume of water lowered <br />in the Pit as much as is practicable through use of the water in the production of cement. Upon cessation of <br />mining and cement production, the pit will be capped and reclaimed in accordance with the approved plan. <br />If there are any questions regarding the above information, our proposed monitoring programs, or the <br />attachments, please contact Denise Arthur at 303 517-3043. <br />Sincerely, <br />Demse Arthur, Ph.D. <br />Environmental Manager <br />ATTACHMENTS: <br />Table 1: Water Monitoring Analytical Data, 2010 <br />Figure 1: Selenium Concentrations in C-Pit Pond and Groundwater at CEM-001 <br />Figure 2: Selenium Concentrations in C-Pit Pond and Groundwater at CEM-004 <br />Figure 3: Water Elevations v. Time <br />4