The Aurora Mine Mill Facility (previously Esmeralda Mill) is located in the historic Aurora mining district of the eastern Sierra Nevada Mountain Range in Nevada, USA. Aurora recently, with the support of Tierra Group completed a Minor Modification to the Mine’s Water Pollution Control Permit (WPCP) to recommence operation of the Mine’s mill and allow the processing of historical tailings from Tailings Storage Facility 1 (TSF1). The reprocessed mill tailings will be deposited in Tailings Storage Facility 2 (TSF2) which is a fully lined tailings facility commissioned in 2012. Both tailings facilities are comprised of a jurisdictional tailings dam. Tierra Group serves as the Engineer of Record for both dams. Modifications to the WPCP designed by Tierra Group also included a new concrete containment pad, relining of several ponds, and preparation of a revised closure plan for TSF1.

Tailings management at Aurora is unique and challenging due to its high elevation (7,000 feet amsl) in a high seismic region with a relatively arid climate that experiences snowfall during winter months. As Engineer of Record, Tierra Group provides engineering consultancy, design and construction related engineering services for both of Aurora’s TSFs.

Weather Station Siting Assessment

In 2020, Tierra Group completed a site assessment for a weather station to be installed at the site. The assessment evaluated the foundation conditions and provided recommendations regarding anchoring options for the weather station tower and ancillary components. The assessment also identified hazards that may affect the weather station’s operation.

Annual Dams Inspection Aurora Mine

In 2020 and 2021, Tierra Group is the Engineer of Record (EoR) for two tailings dams at the Aurora Mine. Tierra Group provided annual dam safety inspections for the tailings dams to meet Nevada Division of Water Resources (NDWR) Dam Safety permit requirement. Work included a site visit, visual observation, instrumentation data review, and dam inspection report preparation.

Aurora TSF1 FPCP & TSF2 Closure Review

In 2021, Tierra Group evaluated and prepared the closure design for Aurora's TSF1 facility. Design components included civil grading of closure surface, stability analysis of closure slopes, and hydraulic design of channels and spillways. A final design support was prepared by Tierra Group for submittal to regulatory agencies for approval. Subsequently in 2022, Tierra Group prepared final permanent closure designs for TSF 1. As part of closure permitting a Decommissioning Plan was prepared for submittal to the Nevada Division of Water Resources.

Engineer of Record (2022, 2023)

Tierra Group is the Engineer of Record (EoR) for Tailings Storage Facility (TSF1) and TSF2. Tierra Group designed the Water Pollution Control Permit (WPCP) modifications, including a new concrete containment pad, relining several ponds, and a revised closure plan for TSF1. In addition, Tierra Group provided annual dam safety inspections for the tailings dams to meet Nevada Division of Water Resources (NDWR) Dam Safety permit requirements.

The EoR work consisted of a site visits, visual observations, instrumentation data reviews, and annual dam inspection reports for each dam. Tierra Group completed a more detailed assessment and evaluation of the South Diversion Channel in 2023 due to slope instability/erosion/sloughing in response to the extremely wet winter (high snowmelt).

Tierra Group provided engineering consultancy, design, and construction-related engineering services for both TSFs.