2017-05-12_PERMIT FILE - C2010089A (4)

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dewatering is required, the anticipated dewatering rate will be in the range of one to two cubic feet per second or less. Direct pit pumping into Pond NHN-001 or NHN-002 is planned for the mining south of Meehan Draw and into Pond NHN-003 for the mining north of Meehan Draw. Actual water flow velocity going into ponds will be controlled with adequate erosion control (i.e., rock riprap, geotextiles, synthetic liner, half -culverts, etc.) or discharged onto non -erodible bedrock material. This will minimize erosion of the pond banks. Pit dewatering will have an insignificant impact on the ponds. Pit dewatering will be sporadic versus continuous. The flow rate of one to two cubic feet per second or less compared to the designed 10 -year, 24-hour peak inflow rate the ponds were designed for is relatively insignificant. Monitoring for rills and gullies on the pond slopes will be carried out on a periodic basis; the monitoring being geared to those periods after spring snow melt and during required quarterly pond inspections. Occurrence of excessive rills and gullies will result in implementation of necessary maintenance. Remedial action on pond slopes will extend as far down the slopes as equipment access allows. Design Methodology Appendix 2.05.3(4)-1 includes the methodology used for the initial pond designs. Pond NHN- 002 has been redesigned, with all details included in Appendix 2.05.3(4)-8. Special Features Temporary Relocation for CC Company Second Park Lateral Ditch The Colorado Cooperative Company has operated an irrigation ditch known as the Second Park Lateral Ditch to irrigate lands in the area for many decades. With the mining of the Garvey property, this ditch has been diverted. Since the temporary diversion route involves rises and dips, a pipeline has been used. Map 2.04.7-9 2nd Park Lateral Pipeline Location, shows the location of the pipeline's temporary route and the permanent relocation. As per the successful experience at NH2 Mine, a high density polyethylene (HDPE) pipeline was installed for the temporary route and will also be utilized for the permanent route. Although expensive, NHN believes this design will best suit the long term needs of the CC Ditch Company. Prior to construction, NHN evaluated multiple temporary diversion routes for the pipeline. The route that was selected begins at the eastern mine permit boundary and follows County Road 26.50 south then turns to the west around the mine permit boundary parallel to County Road AA and then turns north along County Road 26.00 Road to tie into the existing ditch. Once mining moves north of the Garvey property and the area is restored to its approximate original contour, the temporary line can be moved into the permanent location. Section 2.05.3(4) Page 4 February 2017 (TR -15)