Former Brukunga Mine Site (SA) Lessons of a long-term remediation strategy

Transcription

1 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

2 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

3 Background Location History - The Mine Site features The issue The Impact

4 Brukunga Mine Site Location

5 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.

6 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.

7 Brukunga Mine Site The issue cross section looking North Geological setting Hydrogeological and geochemical processes Acid and metalliferous drainage (AMD) release

8 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 flows and 43 in a straight line affecting along the way, farm land, agriculture and ecosystems Heavy metal pollution. - The Brukunga mine impacted on a socio-ecological system. The 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. Dawesley Creek downstream properties cannot currently use the water from the creek. - Downstream landholders rely on subsidised water supply. Financial and environmental liability to Government. - Without remediation the AMD is likely to continue for 750 to 1,000 years. Freeway Brukunga Extent of historic AMD contamination Langhorne Creek In 2001, Government commited $26m to conduct remediation works and improve water quality in Dawesley Creek. Lake Alexandrina

9 Brukunga Remediation Strategy Remediation strategy Remediation framework

10 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

11 Brukunga Remediation Framework Program Program Structure Goal / Outcomes REMEDIATION PROGRAM (long term) Remedia tion Program Phase 1& 2 Assessment & Definition & Feasibility Environmental Audit (Phase1) Phase 3 Design & Costing Phase 4 Days Ck Implementation 2016 Program Assessment (Options Paper) & Forward Program Phase 5&6 Days Ck Monitoring & Validation Phase 7 Whole of Mine Remediation Environmental Audit (Phases 2&3) t = long term t = long term Stop ongoing AMD treatment Land rehabilitated to productive use Water in Dawesley Creek - Fit for use Defining WQ Criteria Pre-mine Surface Water Quality Toxicological Risk Assessment Toxicity Assessment of Pulsed Discharges Sustained Water Quality Irrigation & livestock WATER QUALITY PROGRAM (short/ medium term) Water Management AMD Interception & Treatment Dawesley Creek Diversion Extension Process Improvement - WTP Automation 1st Stage Acid Water Retention Pond Asset management - WTP upgrade & Automation 2nd Stage t = 1-2 years EPA Process Water Quality criteria / Fit for use Stop supply of water to six properties downstream Monitoring & Control In situ monitoring Loggers Real time Monitoring 3G or telemetry Risk Management Plan Remediation of the site that requires 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 11 Brukunga Water Monitoring Program 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, )

12 Long term: Mine remediation Remediation model Design features

13 The remediation model 13 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 ( ) - Phase 2 Option definition & Feasibility ( ) - Phase 3 Days Creek detailed investigation & design ( ) - Phase 4 Implementation (subject to funding)

14 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

15 Short / medium term: Water Quality Dawesley Creek Diversion Water Treatment Water Quality

16 Dawesley Creek Diversion 1.7 km (2004) 260m extension (2014)

17 Water Treatment Lime based neutralisation plant Lime AMD ph=2.5 IN: kl/h Acid water (Sulfuric acid + dissolved metals) High Density Sludge (HDS) Process ph=9.5 Lime slurry tank Lime/ sludge tank Reactor 1 tank Thickener 12m Air Reactor 2 tank ph= OUT: Treated water TSS < 10 NTU Sludge recycling OUT: Sludge (gypsum+metal hydroxides)

18 Water Treatment & Water Quality - ph

19 Water Treatment & Water Quality - Cadmium

20 Water Quality improvements Brukunga Nairne Mine Site <1 km With reference to agriculture irrigation & livestock quality standards (ANZECC) Extent of Contamination (outside flood events) Dawesley Creek Bremer River 20 km Extent of Contamination Langhorne Creek Wine Region 43 km Extent of Historic Contamination s 1980 s Lower lakes

21 Where are we at timeline $26.1m

22 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 (Agriculture irrigitation / livestock ANZECC 2000). While the concentration of contaminants in the water are managed by interception and treatment ( ML of acid water per year), this is not a permanent solution due to volatility from rainfall events.. Treatment would be required for 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.

23 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.

24 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

25 Former Brukunga Mine Site (SA) Lessons of a long-term remediation strategy THANK YOU Raul Mollehuara Project Director / Operations Brukunga Mine Site raul.mollehuara@sa.gov.au