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<br />February 25, 2011 <br />Mr. Michael Cunningham ,/ <br />Environmental Protection Specialist <br />Division of Reclamation, Mining and Safety <br />1313 Sherman Street, Room 215 <br />Denver, Colorado 80203 <br />Re: CEMEX Lyons Mine Permit M-1977-208 <br />Proposed Technical Revision No. 11 <br />?C-Pit/Groundwater Monitories <br />VIA FEDEX Priority Overnight <br />TRK # 796813439970 <br />RECEIVEn <br />MAP 0 12011 <br />Mining and Safety <br />Dear Mr. Cunningham: <br />This proposed Technical Revision No. 11 (TR11) and letter report is in response to CEMEX meetings with <br />Division of Reclamation, Mining and Safety (DRMS) on August 2, 2010, November 4, 2010, December 3, <br />2010. <br />The objectives of TR 11 include the following: <br />• Summarize C-Pit and groundwater data collected since late 2006 through 2010. <br />• Assess the available data for trends. <br />• Outline revisions to the monitoring program defined by Technical Revision No. 9. <br />• Discuss the timeline for the eventual backfilling of the cement kiln dust (CKD) storage area in C-Pit. <br />Background <br />Since October 2007, CEMEX has sampled C-Pit water and groundwater from wells CEM-001 and CEM-004 <br />as required by Technical Revision No. 9 (TR 9) to permit M-1977-208. Sampling has been conducted for <br />thirteen consecutive quarters and submitted as quarterly reports to DRMS. TR 9 required five quarters of <br />monitoring. CEMEX consultant Brown and Caldwell (BC) has compiled the relevant C-Pit and groundwater <br />sampling data collected since 2006 to present and has created the attached figures. <br />Monitoring wells (CEM 001-005) were drilled to assess the hydraulic connectivity between C-pit and down <br />gradient areas and to assess if there was any geochemical connectivity between C-pit and adjacent areas. Data <br />from CEM-001 and CEM-003 indicates that C-pit may influence the wells with regard to water head <br />fluctuations. CEM-002 showed no connectivity to C-pit and has been consistently dry. CEM- 004 located <br />north of C-pit showed no geochemical influence from C-pit. CEM-005 was not influenced by changes in C- <br />pit water levels and it was determined that it is extremely unlikely that water from C-pit could connect with <br />the St. Vrain aquifer. CEM-005 has now been abandoned. <br />The filling of C-Pit with mine overburden, in the spring of 2007, displaced the water and raised the hydraulic <br />head in the fractured bedrock system that contains C-Pit. Further, as indicated by the quarterly data <br />submitted to DRMS under TR 9, geochemical reactions between the pit water and backfilled material lowered <br />pit water pH and dissolved selenium. <br />Please refer to the BC C-Pit Hydrogeologic Investigations Report Dated August 31, 2007 for figures, cross <br />sections, and details on the hydrology and monitoring well network in the C-Pit area, and the initial data <br />interpretations.