Former Brukunga Mine Site (SA) Lessons of a long-term remediation strategy Dealing with Derelict Mines 2016 Raul Mollehuara Project Director / Operations Brukunga Mine Site Overview - Background - Brukunga Mine site: Location, history and site features - The issue and the impact - The remediation strategy - The Strategy & Objectives - The remediation framework - The long term program - Mine Remediation - Remediation model - Design Features - The short / medium term program - Water Quality - Dawesley Creek diversion - Water treatment - Water quality - Where are we at - Lessons learned Background Location History - The Mine Site features The issue The Impact Brukunga Mine Site – Location Brukunga Mine Site – history • Mining 1950’s through to 1970’s. Mine sponsored by the State Govt. Production subsidy by the Federal Government • Produced 5.5 Mt ore (11% Sulphur: Pyrite & Pyrrhotite) and concentrated in a flotation process. • The concentrate railed to Pt Adelaide for further processing into sulphuric acid to produce fertiliser. Brukunga Mine Site – Features • 165 Ha • Open pits • 8 Million tonnes waste rock • 3.5Million tonnes of tailings • Water Treatment Plant • Township • Other users of the site: CFS, DET CRC, Boart Longyear, TAFE SA, RTOs, Research groups. Brukunga Mine Site – The issue cross section looking North • Geological setting • Hydrogeological and geochemical processes • Acid and metalliferous drainage (AMD) release Brukunga Mine Site – The impact Not just about the site, water is the main transport mechanism. These waters from the Brukunga site nearly 70kms as the creek Brukunga flows and 43 in a straight line affecting along the way, farm land, agriculture and ecosystems Extent of Heavy metal pollution. historic AMD - The Brukunga mine impacted on a socio-ecological system. The contamination system consists of the Dawesley creek, the Bremer river and Lake Alexandrina, and importantly – all the associated terrestrial adjacent ecosystems, and the local families and businesses using these ecosystems. Freeway Dawesley Creek downstream properties cannot currently use the water from the creek. - Downstream landholders rely on subsidised water supply. Langhorne Creek Financial and environmental liability to Government. - Without remediation the AMD is likely to continue for 750 to 1,000 years. In 2001, Government commited $26m to conduct remediation works and improve water quality in Dawesley Creek. Lake Alexandrina Brukunga Remediation Strategy Remediation strategy Remediation framework Brukunga Remediation Strategy The objectives of the remediation are to: • Improve water quality in Dawesley Creek to a standard as good as possible. • Substantially limit or avoid the need to intercept and treat acid waters indefinitely. • Return all or part of the site back to productive uses or for environmental/ ecosystem values. • Apply leading practice to site management and mine completion. The strategies at the site: 1. Short / medium term program: Ensure water in Dawesley Creek meet quality standards. 2. Long term program: Mine completion through to full remediation. Since 2007 an expert Technical Advisory Group (TAG) has overseen extensive testing to develop a technically feasible remediation strategy. Comprised of internationally respected experts in the field of AMD management and mine remediation, the TAG has provided guidance and assessed a program of technical studies to identify a suitable whole-of-site strategy to remediate the site. 10 Brukunga Remediation Framework Program Program Structure Goal / Outcomes 2007-2011 20012-2015 2017+ Phase 1& 2 Remedia Phase 3 Design Phase 4 Days Ck Phase 5&6 Days Ck Phase 7 Whole of Mine t = long term Stop ongoing AMD Assessment & Definition & tion & Costing Implementation Monitoring & Validation Remediation treatment Program Feasibility 2016 Program Assessment Land rehabilitated to (long term) (Options Paper) & productive use Forward Program REMEDIATION PROGRAM PROGRAM REMEDIATION Environmental Environmental t = long term Audit (Phase1) Audit (Phases 2&3) Water in Dawesley Creek - Fit for use Defining Pre-mine Surface Toxicological Risk Toxicity Assessment of Sustained Water Quality WQ Water Quality Assessment Pulsed Discharges – Irrigation & livestock Criteria EPA Process – Water Quality criteria / Fit for use Water Dawesley Creek Acid Water Management Diversion Extension Retention Pond Stop supply of water to six properties AMD Process Improvement Asset management downstream Interception 1-2 t = years - WTP Automation 1st - WTP upgrade & Automation & Treatment (short/ medium term) (short/ medium Stage 2nd Stage WATER QUALITY PROGRAM PROGRAM QUALITY WATER Monitoring In situ monitoring – Real time Monitoring – 3G Risk Management ‘Remediation of the site that requires & Control Loggers or telemetry Plan no further intervention by, ongoing responsibility for or cost to government and / or community’ Consultative gateways Relinquish EPA licence and discontinue: Ongoing Water Treatment Plant Operation and Property Maintenance Brukunga Water Monitoring Program 11 Third Party users and opportunities: Mine Skill Centre Framework (Organic growth), commercial activities (filming, technology testing, etc) Opportunities for Research & Collaboration (geosciences, mine exploration, mine remediation & rehabilitation, …) Long term: Mine remediation Remediation model Design features The remediation model • A solution concept that is technically feasible for a long term remediation of the site was developed by the TAG – The Saturated co-disposed waste model that involves the compaction and saturation of co-disposed (mixed) waste rock, tailings and limestone, contained by mine voids and an embankment, under an engineered cover system. • Given the nature and cost of the remediation works the site has been divided into domains: Days Creek, Dawesley Creek and Taylors Creek (with Days Creek as the section of the mine to be remediated first) • The long term remediation program is a phased program: - Phase 1 – Development and assessment of remediation options (2007-09) - Phase 2 – Option definition & Feasibility (2009-11) - Phase 3 – Days Creek detailed investigation & design (2012-15) - Phase 4 – Implementation (subject to funding) 13 Design features – Days Creek domain • Section of mine to be remediated first – contains approximately 800,000 m3 of waste rock and tailings. • Co-disposing waste rock and tailings with limestone. High infiltration cover to maximise rainfall into the co-disposed material. • Seepage control to limit the loss of water. Co-disposed waste 60.5% Waste Rock 35.5% Tailings 4.0% CaCO3 Short / medium term: Water Quality Dawesley Creek Diversion Water Treatment Water Quality Dawesley Creek Diversion 1.7 km (2004) 260m extension (2014) Water Treatment – Lime based neutralisation plant High Density Sludge (HDS) Process Lime AMD IN: 75 – 100 kL/h pH=2.5 Acid water (Sulfuric acid + dissolved metals) pH=9.5 Lime slurry tank Lime/ sludge tank Reactor 1 tank Thickener 12m¢ Reactor 2 Air tank pH= 9.0 – 9.5 OUT: Treated water TSS < 10 NTU Sludge recycling OUT: Sludge (gypsum+metal hydroxides) Water Treatment & Water Quality - pH Water Treatment & Water Quality - Cadmium Water Quality improvements With reference to agriculture Mine Site irrigation & livestock quality Brukunga standards (ANZECC) <1 km Extent of Contamination 2014+ Nairne (outside flood events) Dawesley Creek Bremer River 20 km Extent of Contamination 2004 ‐2014 Langhorne Creek Wine Region Extent of Historic Contamination 20 43 km 1950’s ‐1980’s Lower lakes Where are we at – timeline $26.1m Where are we at – key points • Brukunga former mine site is a 165 Ha property that requires ongoing management. • Water quality has improved significantly and contamination has been reduced in the zone of influence from 40km in 1980 to less than 1km in 2014+ (Agriculture irrigitation / livestock – ANZECC 2000). • While the concentration of contaminants in the water are managed by interception and treatment (120- 150 ML of acid water per year), this is not a permanent solution due to volatility from rainfall events.. Treatment would be required for 700-1000 years. • More than $35 million has already been spent on operational and capital costs over last 30 years. Approximately $700k annual cost to Government (incl. treatment of acid water plus maintenance of the site) • A technical rehabilitation solution has been developed and can be implemented quickly or can be staged over a longer timeframe subject to funding. • Detailed design, engineering and costing (Phase 3) have been conducted for the first domain – Days Creek ($35 million). The cost of remediating one domain gives an insight into the scale and long-term cost of remediation. Lessons learned Technical • A better understanding of the remediation concept and its interactions with the site characteristics (e.g. hydrology, hydrogeology, geochemistry, geology, erosion and landform evolution, soil hydrology, cover systems, revegetation, climate change). • A better understanding of the saturated co-disposed waste model. Proof of concept through laboratory testings and field trials. Strategies to overcome constructuability issues and challenges (e.g. compaction rates due to heterogenetity of waste rock particle sizes). Regulatory • Knowledge areas to support regulatory function of the Mining Regulation Branch in South Australia regarding PEPRs and closure plans. Other beneficial uses: Third Parties Drilling Technologies for Exploration: (Deep Exploration Technologies CRC / Boart Longyear) Training (SACOME, TAFE SSA, RTOs) County Fire Services (CFS) Films & Commercials 24 Former Brukunga Mine Site (SA) Lessons of a long-term remediation strategy THANK YOU Raul Mollehuara Project Director / Operations Brukunga Mine Site [email protected].