Laserfiche WebLink
Page 2 of 2 <br />Sequencing of under -drain construction and overburden placement <br />DRMS would like Climax to provide, to the maximum extent possible, a more detailed description of the <br />proposed sequencing of surface preparation, under -drain construction/certification, and waste rock placement for <br />the North40 and McNulty OSF areas. <br />Final Design(s) <br />DRMS acknowledges that some final design decisions regarding piping sizes, bedding material, liner width, etc. <br />for the under -drain and water handling system have not been made at this time; and that Climax will be collecting <br />the necessary field data to support those design decisions in the coming months. Because this information is not <br />currently available for review, Climax will need to commit to submitting all future certified final construction <br />designs to DRMS for review and approval before construction begins. <br />Demonstration of stability of existing ground conditions <br />Please demonstrate the stability of the existing ground conditions, and suitability of the area for the proposed OSF <br />construction and material placement methods with appropriate FOS modeling and discussion. This should <br />include cross section(s) through the existing OSFs and the mapped landslide area(s) using conservative <br />assumptions such as remolded values for slide -plane material cohesion and an elevated groundwater surface to <br />represent seasonal fluctuations in existing seep /spring areas, as well as appropriate seismic event stresses. Does <br />this analysis show 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 prior to or during <br />the proposed OSF construction to insure long term stability? <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 present until the end <br />of mine life. What actions (re- grading, temporary covers, etc) will Climax take with respect to the OSF facilities <br />during period(s) of extended inactivity (greater than 12 -18 months) in one or all active OSF areas? <br />OSF "Worst Case" Failure Scenario <br />As a standard preparedness exercise, using assumptions consistent with the current OSF design and FOS <br />modeling, what are the failure threshold scenario(s) for the proposed design? (Seismic event, precipitation event, <br />material saturation levels, over - loading, other ?) What are the "plausible threshold limits" for combinations of risk <br />factors that will need to be mitigated, monitored for or avoided? Have any analyses have been completed (other <br />than rolling rock) to determine the failure risk scenarios for impacts to existing infrastructure (such as that listed <br />in section 2.1.3 of the TR22 submittal or Highway 91). <br />This concludes the Division's adequacy review of TR22. This letter shall not be construed to mean that there are no <br />other technical issues in the submittal. Other issues may arise as additional information is supplied. As stated <br />previously, DRMS is committed to working with Climax to implement a "best available practice" approach for <br />overburden storage for this site that will allow mining to continue while implementing all reasonable environmental <br />protections in compliance with DRMS rules. DRMS is open to additional meetings with Climax if it would be <br />useful to help resolve any remaining issues. <br />If you have any questions, please contact me at (303) 866 -3567 x8140. <br />Sincerely, <br />Eric Scott <br />Environmental Protection Specialist <br />