Mollehuara-Brukunga SA-Derelict Mines 2016 PDF

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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

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The issue and the impact

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The remediation strategy -

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The Strategy & Objectives The remediation framework

The long term program - Mine Remediation -

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Remediation model Design Features

The short / medium term program - Water Quality -

Dawesley Creek diversion Water treatment Water quality

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Where are we at

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Lessons learned

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

Brukunga Mine Site – Location

Brukunga Mine Site – history

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Mining 1950’s through to 1970’s. Mine sponsored by the State Govt. Production subsidy by the Federal Government

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Produced 5.5 Mt ore (11% Sulphur: Pyrite & Pyrrhotite) and concentrated in a flotation process.

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The concentrate railed to Pt Adelaide for further processing into sulphuric acid to produce fertiliser.

Brukunga Mine Site – Features •

165 Ha

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Open pits

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8 Million tonnes waste rock

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3.5Million tonnes of tailings

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Water Treatment Plant

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Township

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Other users of the site: CFS, DET CRC, Boart Longyear, TAFE SA, RTOs, Research groups.

Brukunga Mine Site – The issue

cross section looking North

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Geological setting

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Hydrogeological and geochemical processes

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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 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.

Brukunga

Extentof historicAMD contamination

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.

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Substantially limit or avoid the need to intercept and treat acid waters indefinitely.

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Return all or part of the site back to productive uses or for environmental/ ecosystem values.

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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.

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Brukunga Remediation Framework Program

Program Structure

REMEDIATION PROGRAM (long term)

2007-2011 Remedia tion Program

Goal / Outcomes

20012-2015

Phase 1& 2 Assessment & Definition & Feasibility

2017+

Phase 3 Design & Costing

Phase 4 Days Ck Implementation

Phase 5&6 Days Ck Monitoring & Validation

t = long term

Phase 7 Whole of Mine Remediation

Stop ongoing AMD treatment

2016 Program Assessment (Options Paper) & Forward Program

Land rehabilitated to productive use

Environmental Audit (Phase1)

t = long term

Environmental Audit (Phases 2&3)

Water in Dawesley Creek - Fit for use Toxicological Risk Assessment

Pre-mine Surface Water Quality

Water Management

Dawesley Creek Diversion Extension

AMD Interception & Treatment

Monitoring & Control

Toxicity Assessment of Pulsed Discharges

EPA Process – Water Quality criteria / Fit for use

Acid Water Retention Pond

Asset management - WTP upgrade & Automation 2nd Stage

Process Improvement - WTP Automation 1st Stage

In situ monitoring – Loggers

Sustained Water Quality – Irrigation & livestock

t = 1-2 years

WATER QUALITY PROGRAM (short/ medium term)

Defining WQ Criteria

Real time Monitoring – 3G or telemetry

Risk Management Plan

Consultative gateways

Ongoing Water Treatment Plant Operation and Property Maintenance Brukunga Water Monitoring Program

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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, …)

Stop supply of water to six properties downstream

‘Remediation of the site that requires no further intervention by, ongoing responsibility for or cost to government and / or community’ Relinquish EPA licence and discontinue:

Long term: Mine remediation Remediation model Design features

The remediation model

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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.

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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)

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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)

Design features – Days Creek domain

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

Lime

High Density Sludge ( HDS) Process

I N: 75 – 100 kL/ h

AMD pH=2.5

Acid wat er ( Sulfuric acid + dissolved met als)

pH=9.5

Lime slurry tank

Lime/ sludge tank

Reactor 1 tank

Thickener 12m¢

Reactor 2

Air

Sludge recycling

tank

pH= 9.0 – 9.5 OUT: Treated w ater TSS < 10 NTU OUT: Sludge (gypsum+metal hydroxides)

Water Treatment & Water Quality - pH

Water Treatment & Water Quality - Cadmium

Water Quality improvements Brukunga

MineSite...