At ATC Williams, when we design a facility, we consider all aspects of closure, from initial concept to technical feasibility, ensuring regulatory compliance through construction, operation, rehabilitation and post-closure monitoring.
We assist clients in managing the risks presented by mine waste management across the entire lifecycle, including decommissioning and rehabilitation.
Our five-stage approach spans the entire project lifecycle, outlined below with relevant project snapshots.
Mine Closure Lifecycle Solutions
Stage 1 – Strategy Selection
Strategy Selection & Site Characterisation
- Assessing the site’s current condition, identifying potential closure issues and hazards
- Comprehensive closure planning considering environmental, social, and economic impacts
- Geotechnical characterisation of mine waste & available rehabilitation materials
- Basis of design including rehabilitation success criteria
- Risk management
- Options identification and assessment
- Life of facility and life of mine production planning
- Designing closure and rehabilitation strategies and obtaining necessary approvals from regulatory bodies
- Stakeholder engagement to address concerns and incorporate input from local communities and other affected parties
Site Strategy – Project Snapshot
| Mt Rawdon Gold Mine – Evolution Mining – QLD, Australia |
| The Mt Rawdon Gold Mine is located west of Bundaberg and some 14 km southeast of Mount Perry in Southeast Queensland. To comply with environmental regulations, the mine needs to increase its capacity for Tailings Storage, and stormwater freeboard. The development and operation of the Mt Rawdon site are regulated by an Environmental Authority (EA).
ATC Williams completed a Life of Mine (LoM) tailings options assessment and Waste Rock Dump (WRD) concept design, including consolidation analysis. Processing operations are currently due to end in FY2025. The mine redevelopment is currently being undertaken by a joint venture comprising Mt Rawdon Operations Pty Ltd (a subsidiary of Evolution Mining), the owners and operators of the Mt Rawdon Gold Mine, and an investor group managed by ICA Partners. The joint venture is currently undertaking a feasibility study into the potential for a pumped hydro facility. Source: https://mtrawdonhydro.com.au/project-overview/ |
Stage 2 – Technical Assessments
Expert Site Assessment & Compliance
- Bearing capacity of soft tailings
- Consolidation and subsidence assessment
- Pit lake recovery and water quality prediction
- Groundwater contaminant transport
- Surface water hydrology
- Cover system design and modelling
- Water flux and infiltration
- Rehabilitation studies, including on-site trials
- TSF Rehabilitation studies, including cover system trials
- Landform geomorphological design
- Erosion and landform evolution
Technical Assessments – Project Snapshots
| Mt Rawdon Gold Mine – Evolution Mining – QLD, Australia |
Evolution Mining engaged ATC Williams (ATCW) to develop and construct field cover system trials for potential cover options for the rehabilitation of the Tailings Storage Facility (TSF). As part of the process, ATCW reviewed existing information regarding rehabilitation and tailings inventories and properties. The cover systems were designed to align with the objectives of the Environmental Authorities, which outlined the requirements for the rehabilitation of the TSF and considered its risk profile. The cover system needs to achieve the following:
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| CONFIDENTIAL – NSW, Australia |
The Client sought to investigate the potential to bring forward the timeline for the closure of their Tailings Storage Facility (TSF) to facilitate the placement of a Waste Rock Dump (WRD) on this facility. The ability to close the TSF in a shorter timeframe is largely dependent upon the existing strength conditions within the TSF, which support the capping and development of a WRD. ATC Williams was engaged to conduct a preliminary investigation of the TSF to assess the existing state of the tailings deposit and the subsequent development of feasible closure capping regimes. We presented five different capping options, all of which provided methods to overcome the site’s challenges, which include very soft coal tailings deposits. The options were presented to the client with emphasis on the timeframes to complete each option, so the client could utilise the TSF as a WRD facility as soon as possible. |
| CONFIDENTIAL – QLD Australia |
The tailings at the mine were expected to be net acid generating (NAG). As a consequence, the tailings would produce acid mine drainage (AMD) in the longer term if left exposed to the atmosphere. To minimise the potential for AMD the tailings needed to be encapsulated and a near-zero flux cover was required to encapsulate the tailings. In 2012, ATCW designed a preliminary concept encapsulation store and release cover with a capillary break layer immediately over the tailings using best estimate soil parameters. In 2013, we reviewed previous site investigation reports and completed a site visit to identify sources of potential construction materials. No natural materials suitable for the capillary break or low permeability layer (LPL) were available. We undertook the crushing of weathered rock construction material to produce both materials as efficiently as was reasonably practical. The concept cover models were refined using laboratory testing data on the produced materials. The concept cover models presented were reviewed and scrutinised at a stakeholder’s design review meeting. In 2014, the construction of three trial cover cells at the Tailings Storage Facility (TSF) was completed and instrumented. Reviews conducted since 2014 indicated that the cover performance meets the design intent. |
Stage 3 – Landform Geomatic Design
Developing Sustainable Landforms
- Storage facilities for waste rock and process tailings, including:
- Capping and cover systems
- Post-mining final landform, including surface water drainage
- Estimation of construction quantities
Geomatic Design – Project Snapshot
| Mt Rawdon Gold Mine – Evolution Mining – QLD, Australia |
ATC Williams is currently working on the Final Landform Assessment. It aims to develop a final landform based on the landform geometry identified in our TSF Conceptual Closure Design Report and inputs from ongoing TSF cover system studies. The assessment will consider governance and regulatory requirements to achieve an acceptable outcome for relevant stakeholders, geotechnical stability (including erosional considerations), hydrological considerations and surface water management. The methodology will be completed in two stages: 1. Options Assessment Workshop & Risk Assessment – Identify a preferred closure strategy and design standards in line with corporate standards and commitments to internal and external stakeholders 2. Final Landform Assessment – Developing a Final Landform, including a cover system, and addressing erosional stability and surface water management for the selected preferred option identified in Stage 1. ATCW is currently undertaking both stage 1 and stage 2 works.
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Stage 4 – Closure Implementation
Innovative Site Rehabilitation
- Closure activities conducted according to the closure plan
- Decommissioning infrastructure, managing and treating waste, rehabilitating land and monitoring environmental impacts
- The goal is to safely and effectively close the mine site, minimise potential environmental impact and ensure that the site is left in a stable and safe landform
- Construction specification
- Inspection and test planning
- Construction supervision
- Instrumentation and demonstration data capture
- As-constructed reporting and certification
Closure Implementation – Project Snapshot
| CONFIDENTIAL – NSW, Australia |
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ATC Williams undertook the detailed design of a 125 m high overburden emplacement area over an in-pit coal tailings storage facility of very low strength. The scope of works comprised conceptual studies, geotechnical investigations, detailed design of tailings capping systems and access ramps, final landform stability assessments, design of monitoring instrumentation, preparation of design documentation and technical specifications, establishment of construction TARPs, and technical supervision and support throughout the capping construction period. The capping design comprises placing a 19 m thick capping platform over the tailings surface to support mine dump lifts of 15 to 30 m. Formation of the capping platform consists of a conventional capping system for the dry and desiccated areas of the tailings surface. A reinforced capping system using high strength woven geotextiles was adopted for the decant pond and wet areas of the tailings surface, where near surface tailings shear strengths of < 1 kPa were identified. The capping design and construction program was structured to enable early access of mine equipment onto the capping surface to speed up the capping process and reduce construction costs. This was achieved through an optimised capping sequence by establishing multiple capping fronts, ballasting weaker areas of the tailings deposit and applying a balanced capping approach to maintain a safe and efficient capping regime. Construction TARPs were established for the capping works in conjunction with implementing fixed survey stations around the storage perimeter to enable detailed scanning and early detection of capping surface movement. Construction of the Capping Works commenced in September 2020. A 19 m thick capping platform was completed in September 2021 to support a mine spoil emplacement area. The capped surface of the Tailings Storage Facility (TSF) was utilised as a mine spoil emplacement facility throughout 2022 and has since been successfully rehabilitated. |
Stage 5 – Advisory Services
Future-focused Strategies
- Post-closure monitoring and compilation of demonstration data
- Conformance assessment
- Independent technical review – ongoing monitoring and maintenance are crucial to ensure the long-term stability and safety of the site
- Monitoring environmental conditions, managing ongoing risks and implementing necessary remedial actions
- Reporting to regulatory authorities and stakeholders and conducting periodic reviews to adapt the closure strategy if needed
In addition to the above, ATC Williams provides Advisory services to clients with interests in facilities used to provide permanent containment of mineralised waste. Typical assignments would include:
- Independent technical review of decommissioning and rehabilitation plans
- Independent review of closure cost estimates
- Review of organisational policy and management requirements to ensure alignment with industry standards such as ANCOLD and GISTM
- Governance and assurance services over the entire facility lifecycle, including post-operations and post-closure EoR and ITRB services
Advisory Assessment Projects provided upon request.
