2013-01-14_PERMIT FILE - M2012032 (6)

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DRMS Comment Map G -5: General Comments 19. Collection ditches are proposed to have 1.5H:1 V side slopes. Side slopes this steep are inherently unstable. Please revise the side slopes to no steeper than 2.5H:1V (3H:1V is preferred). 20. Diversion ditches are proposed to have 2H:1V side slopes. Side slopes this steep are inherently unstable. Please revise the side slopes to no steeper than 2.5H:1V (3H:1V is preferred). SMO Response The ditches have been revised to either have 2.5H:1V side slopes when installed in Pre mine waste rock and Mill tailings. Steeper side slopes (1.5H:1V) are used for the Grouted riprap channels. DRMS Comment 21. Half pipe channel segments are proposed for several steep sections. The use of half pipes typically requires significant maintenance. The Division will accept half pipe channels during the operational phase of the mine, provided the Operator will provide a written commitment to perform frequent inspections and perform the necessary maintenance. However, half pipe channels are not acceptable for reclamation channel design. Please submit alternate designs for the post - mining phase. SMO Response The Revenue Mine surface water controls will be inspected and maintained to ensure that they remain sufficient to control runoff according to DRMS and CDPHE rules and regulations. This inspection and maintenance will continue throughout the life of the mining operation and throughout the post mining reclamation phase, until sufficient revegetation of the site has occurred to protect against erosion, and make stormwater controls redundant. Furthermore, reclamation designs for each channel segment that uses a half pipe during mining have been assembled, per the Division's request. These designs can be found on Map G -5 (labeled with (rec)) and in Table 6 -2 in Appendix 6. DRMS Comment 22. No hydraulic calculations for any channels were provided. Please provide hydraulic design calculations for all engineered channels. Calculations should include channel evaluations for both stability and capacity, i.e., minimum and maximum expected roughness. For example, an excavated earth channel, after weathering would be expected to have a minimum n = 0.018 (use to evaluate stability or maximum expected velocity); and a maximum n = 0.025 (use to evaluate capacity). In addition, the DRMS requires channel freeboard be evaluated for all engineered channels• channels shall be designed with a minimum of 0.5 feet of freeboard unless the velocity head (v /2g) is significant, then the minimum required freeboard is half the velocity head, or v /4g. NOTE — some