2022-09-06_REVISION - M1977300 - Laserfiche WebLink

Home Browse Search

COLORADO LEGACY LAND $CHWARTZWALDER MINE materials within the alluvial pad,can be performed.To allow for access to the contaminated soils in the alluvial valley, the water treatment plant was relocated up to the Mesa in 2018. The previous water treatment plant was demolished,and debris were returned to the underground mine in accordance with the Mine Permit(M- 1977-300). After the alluvial valley excavation is complete and the corresponding disturbed areas are reclaimed,the bypass pipeline and sump system shall be removed. CLL proposes allowing Ralston Creek to flow through the sluice gate at the cut off wall into its natural channel while the bypass pipeline infrastructure remains in place.This would allow CLL to monitor the water quality in Ralston Creek while the bypass pipeline infrastructure is still intact and determine the optimal time for removal. CLL intends to demolish the concrete wall (2 feet thick x 220 feet long x 20 feet high), footer (1 foot x 2 foot x 220 foot), and pipeline cradle foundations (ten total, 5- foot long each). Concrete and other demolition debris shall be broken into manageable pieces for offsite disposal. The bypass pipeline shall be cut into 30-foot sections,loaded on a truck and hauled offsite for disposal. E.4. MITIGATION PLAN FOR SOLID SOURCE TERM MATERIALS AND RECLAMATION PLAN FOR THE ALLUVIAL VALLEY Alluvial valley excavation began in 2018 and has progressed seasonally(late spring to early fall)to present day. In Technical Revision #14, the previous operator, Cotter Corporation presented the baseline scope for the excavation project. This document initially identified 33,000 to 54,0000 cubic yards(CY)cubic yards of soil for removal and onsite disposal in the Minnesota Adit. In accordance with 2013 Mine Plan Amendment 4, contaminated alluvial fill materials were excavated and placed in an underground stope known as the "Glory Hole",which is accessed through the Minnesota Adit of the Schwartzwalder Mine on the hillside well above the elevation of Ralston Creek on the southern side of the valley.When the Glory Hole reached capacity (-56,000 CY),and in accordance with 2021 Mine Plan Amendment 5,additional contaminated materials were placed in the open adit for the Black Forest Mine,a nearby former decorative rock mine that was only partially advanced before operations were permanently terminated. Because Black Forest Mine has recently reach capacity (-15,000 CY), CLL is requesting permission to dispose of additional materials by extending the South Waste Rock Pile (SWRP) to the south/south-east in front of the Former Black Forest Mine (-12,000 CY). CLL shall extend the SWRP consistent with the previously approved construction criteria and reclaim the newly disturbed areas consistent with the MLRP. These criteria are summarized below: • Placement Mao: Appendix 4 contains a plan set that illustrates the placement of materials to extend the SWRP. Technical Revision 14 initially scoped adding materials to the top of the SWRP, however CLL is proposing to extend the pile. This approach reduces the footprint of"new disturbance"and will create a more natural looking • CaR: Disturbed areas shall be capped with 3-feet of cover material. Cap material will be locally sourced from within the permit boundary from either the north side of Ralston Creek near the former laydown area,or from within the alluvial valley excavation area on the south side of Ralston Creek. • Reseeding: Disturbed areas shall be reseeded using the approved seed mix (Table E-1). Additional detail on reseeding is provided in the following section. The true spatial extent of the alluvial excavation project is not fully known.As the excavation work processes, and in accordance with Technical Revision 14, gamma radiation surveys are completed to guide excavations such that material are efficiently and effectively removed based on real time measurements. Figure E-2 illustrates the potential horizontal extent of contamination (up to 6.35 acres) from the most recent surface AUGUST 2022 12 AMENDMENT 6