Tierra Group conducted a siting analysis for a new WRSF to support the mine’s future production increase as part of the Preliminary Feasibility Study (PFS).

In addition to supporting the PFS, Tierra Group assisted in preparing and submitting several engineering design changes (EDC) to increase the existing WRSF’s operating life. The project involved a waste rock dump expansion with civil design and stability modeling to ensure compliance with regulatory dam safety criteria. Tierra Group completed unsaturated modeling to support the WRSF closure cover design for the Waste Rock Repository (WRR), comparing alternative cover configurations to minimize long-term infiltration through reactive waste rock, selected a preferred cover geometry, and completed draindown analyses for both facilities to support site closure and bonding requirements.

In addition, Tierra Group conducted waste rock field sampling and laboratory tests to confirm hydraulic parameters for modeling. The team developed water balance models to monitor meteoric and seepage flows into the WRSF's collection pond. Finally, Tierra Group addressed comments from the Bureau of Mining Regulation and Reclamation (BMRR) related to WRSF seepage site tracking, modeling parameters, and closure designs.

Rapid Infiltration Basin (RIB) Ponds Modification

Tierra Group prepared a minor design modification submittal. The design included converting existing RIBs into double-lined collection ponds with leak detection. In addition, ancillary pipelines and pumps were sized per the mine’s operating requirements. After completing the RIB design, Tierra Group evaluated design options for a hoist system to extract evaporators used in the lined ponds.

Final Plan for Permanent Closure (FPPC)

Tierra Group evaluated and prepared the Fire Creek site-wide FPPC to meet Nevada Division of Environmental Protection (NDEP) requirements. Design components included civil grading of the waste rock closure surface, stability analysis of closure slopes, and hydraulic design of channels and spillways. Tierra Group prepared a final design report for submission to regulatory agencies for approval. Closure activities and design were completed in a phased approach.