Laserfiche WebLink
Final Design(s) <br />DRMS acknowledges that some final design decisions regarding piping sizes, bedding material, <br />liner width, etc. for the under -drain and water handling system have not been made at this time; <br />and that Climax will be collecting the necessary field data to support those design decisions in <br />the coming months. Because this information is not currently available for review, Climax will <br />need to commit to submitting all future certified final construction designs to DRMS for review <br />and approval before construction begins. <br />Response: Climax will provide the necessary designs for DRMS review and approval prior to <br />construction. <br />Demonstration of stability of existing ground conditions <br />Please demonstrate the stability of the existing ground conditions, and suitability of the area for <br />the proposed OSF construction and material placement methods with appropriate FOS modeling <br />and discussion. This should include cross section(s) through the existing OSFs and the mapped <br />landslide area(s) using conservative assumptions such as remolded values for slide plane <br />material cohesion and an elevated groundwater surface to represent seasonal fluctuations in <br />existing seep /spring areas, as well as appropriate seismic event stresses. Does this analysis show <br />any areas of concern (mapped slide areas, potentially unstable areas, existing OSFs, or other <br />areas) that will require special surface preparation, material segregation, or other modifications <br />prior to or during the proposed OSF construction to insure long term stability? <br />Response: Golder has reviewed site topography and photographs taken during the 2011 field <br />investigation. During the review, Golder did not identify any signs of significant slope <br />instability or historical landslides. However, the Colorado Geological Survey Landslide <br />Inventory does show a potential landslide hazard area in the northeast corner of the proposed <br />McNulty OSF site. Golder performed a supplemental stability analysis to evaluate the impact of <br />OSF construction, assuming that the area indicated by the CGS Landslide Inventory is indeed a <br />historical landslide. The results of the supplemental stability evaluation are presented in <br />Attachment 1 to this letter, and show that the overburden placed during construction will act as a <br />buttress, increasing the static factor of safety to 1.8 (above the minimum required value of 1.4). <br />Plan(s) for extend period(s) of inactivity for part or all of OSF areas <br />The submitted OSF design appears to assume constant material placement activity from the <br />present until the end of mine life. What actions (re- grading, temporary covers, etc.) will Climax <br />take with respect to the OSF facilities during period(s) of extended inactivity (greater than 12 -18 <br />months) in one or all active OSF areas? <br />Response: Climax will evaluate the need for additional water management controls in areas that <br />experience prolonged inactivity on a case -by -case basis. This evaluation will include field <br />inspections to determine if water is ponding on surfaces and whether there is adequate drainage <br />to the toe berms /diversions described previously. No temporary covers are anticipated since <br />compaction of OSF surfaces occurs during material placement and positive drainage will be <br />maintained during OSF construction, which will minimize infiltration on OSF tops. All contact <br />water runoff from slopes will be contained by the toe diversions. If needed, additional grading <br />and/or excavation of surface ditches to facilitate drainage off of OSF areas could be performed. <br />4 <br />