2018-06-08_REVISION - C1981010 (4)

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2 Trapper Mine: Technical Revision TR119 Prepared by: R. Reilley Date: June 2018 Second ADQ for Trapper TR119 Please address the following items. March 2018 DRMS 1. For each topsoil stripping area, (haul road, N Pit and L Pit), please describe how stripped topsoil will be handled and where it will be stored or deposited. Trapper Response: Topsoil will be handled in accordance with Section 3.2 of the permit. In the L-Pit area topsoil will either be removed and replaced on adjacent reclamation or stored in piles near future reclamation west of the pit. In N-Pit topsoil will be removed and stored in nearby piles local to the pit area. June 2018 DRMS Adequate 2. Please describe and or illustrate where and how runoff from N Pit will be routed. Trapper Response: All pit disturbance runoff will flow to the East Pyeatt sediment ponds. Minimal runoff associated with the haul road stripping and construction area will flow to the Grouse sediment ponds. Some temporary diversion ditches may be used to carry flows from adjacent reclamation around the south side of the pit during mining. Ditches would be temporary in nature and be designed and built using the temporary ditch designs in section 4.8.1.2 of the permit. If larger structures are required they will be evaluated at a later date. June 2018 DRMS Adequate DRMS notes that minimal disturbed area runoff will flow to the Grouse sediment ponds. DRMS does not regulate NPDS permit requirements as per the Memorandum of Understanding with Colorado Department of Health and Environment (CDPHE). However, DRMS notes that as per the March 2017 Draft of TMI’s discharge permit #CO0032115 to Grouse Gulch is permitted to receive stormflow from: o reclamation o topsoil stockpile and an o inactive haul road Given that the haul road disturbance comprises 3.3 acres and will be active, DRMS recommends that TMI communicates these new mining conditions to CDPHE. For DRMS to issue a decision, it is unnecessary for Trapper to provide the Division additional documentation. 3. Please demonstrate through SEDCAD or other means, the capacity of specified sediment ponds to treat the runoff expected from N Pit stripped area. Trapper Response: SEDCAD modelling for the East Pyeatt drainage was updated with the approval of PR-05. Based on this model and the parameters used to complete it, new disturbance resulting from topsoil stripping in 2018 will not be in excess of the original design. A comparison was made of acres of active mining and disturbance in the SEDCAD model and current conditions with N-Pit stripping included. In the model, active areas are given a curve number of 87. A total of 391.7 acres were included as active in the original model compared to 338.68 acres if all 2018 N - Pit stripping was completed. Also of note is the 2 year growth (CN 67) category at 461.5 acres in the original model compared to 675.57 acres cu rrently with 2018 N-Pit stripping removed. Slopes are also less steep in the proposed stripping areas for N-Pit and should also reduce runoff potential. The East Pyeatt sediment ponds have the capacity to treat proposed 2018 topsoil stripping within the N-Pit area based on this comparison. Curve number 87 active areas are less than the original model and the 2 year growth areas have increased as much of the watershed within F-Pit to the south of N-Pit has attained Phase II and III bond release.