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Mr. Michael Cunningham <br /> CEMEX Sandstone Quarry—Response to Preliminary Adequacy Review Comments <br /> Permit M-1977-361 <br /> July 1, 2014 <br /> Earth Technologies, Inc. performed the hydrologic and hydraulic analysis of the outlet channel and <br /> culvert, and produced the three aforementioned figures, but was not in responsible charge of aspects of <br /> the pit design that pertain to the highwall and its stability and therefore cannot sign Figure E1 as per the <br /> Colorado Bylaws and Rules of The State Board of Licensure for Architects, Professional Engineers and <br /> Professional Land Surveyors. <br /> CEMEX Response 9b: Owners of record of land with two hundred feet of the affected area are shown on <br /> Figure A-4. Additionally the owner of record of the surface area, the substance to be mined, and the type <br /> of structure and owners of record of any permanent man-made structure within two hundred feet of the <br /> affected area have been added to Figure A-4. <br /> CEMEX Response 9c: All major features to be used in connection with the proposed operation have <br /> been added to Figure E-1 including existing roads and topsoil stockpiles. <br /> CEMEX Response 9d: The area where material extraction will continue to the south and west have been <br /> added to Figure E-1 along with other areas that will be cut as a part of final reclamation. <br /> 6.5 Geotechnical Stability Exhibit <br /> Comment 10: Please address the comments provided in the attached Memo regarding the stability <br /> analysis for the highwall. <br /> CEMEX Response 10: A response to this comment has been prepared by Engineering Analytics and is <br /> attached to this letter along with other supporting documentation. Water and Earth Technologies, Inc. has <br /> also provides some additional information regarding surface water control around the highwall <br /> Comment 10e. Please provide comment on how surface water control will be established around the <br /> highwall. <br /> CEMEX Response 10e: Diverting stormwater around the pit has several drawbacks and is therefore not <br /> proposed as part of the final pit configuration. The undisturbed slope above the pit generally varies from a <br /> 5:1 slope to a 3.5:1 slope. Forcing overland sheetflow runoff to abruptly turn 90 degrees and flow across <br /> the slope in a diversion channel will be difficult to accomplish and could potentially lead to long term <br /> stability issues and long-term diversion channel maintenance. First of all, due to the momentum effects of <br /> water, up-gradient runoff will have a tendency to overtop the diversion instead of making a 90-degree <br /> turn. Concentrated stormwater conveyed in the diversion will contain some sediment load, and the <br /> diversion could generally lose capacity over time due to siltation. During a major runoff event, localized <br /> breaches in the diversion and/or localized areas of overtopping are expected. This localized concentration <br /> of flow could increase potential for erosion and instability along the top of the pit highwall, on benches and <br /> at the reclaimed pit floor. Additionally, concentrating flow in a diversion channel at the top of the highwall <br /> can increase the potential for infiltration thereby increasing the potential for instability in both the <br /> upgradient slope and the highwall. Allowing surface runoff to flow overland and sheetflow over the <br /> highwall is proposed. This is the configuration that has already existed for several years with no evidence <br /> of slope or highwall instability. <br /> CEMEX appreciates DRMS's consideration of these responses and looks forward to receiving approval of <br /> AM-01. Please contact me at 303.823.2115 if you have any remaining questions or comments. <br /> Sincerely, <br /> 1 <br /> �'Lj" <br /> Michael Whitehead <br /> Environmental Manager <br /> Page 4 of 4 <br />