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

Dealing with Derelict Mines 2016

Raul MollehuaraProject 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

LocationHistory - The Mine

Site featuresThe issue

The Impact

Background

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 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.

In 2001, Government commited $26m to conduct remediation works and improve water quality in Dawesley Creek.

Brukunga

Freeway

Langhorne Creek

Lake Alexandrina

Extent of historic AMD contamination

Remediation strategyRemediation framework

Brukunga Remediation Strategy

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.

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Brukunga Remediation Framework

Dawesley Creek Diversion Extension

Acid Water Retention Pond

Water in Dawesley Creek - Fit for use

Phase 1& 2Assessment & Definition &

Feasibility

Phase 3 Design & Costing

Phase 4 Days CkImplementation

Pre-mine Surface Water Quality

Environmental Audit (Phase1)

Brukunga Water Monitoring Program

Program Structure

Consultative gateways

Asset management- WTP upgrade & Automation

2nd Stage

Process Improvement- WTP Automation 1st

Stage

Toxicological Risk Assessment

Toxicity Assessment of Pulsed Discharges

Real time Monitoring – 3G or telemetry

Risk Management Plan

Defining WQ

Criteria

Water Management

AMD Interception & Treatment

In situ monitoring –Loggers

EPA Process –Water Quality criteria /

Fit for use

Sustained Water Quality – Irrigation & livestock

Monitoring & Control

Program Goal / Outcomes

Land rehabilitated to productive use

Phase 5&6 Days CkMonitoring & Validation

Phase 7 Whole of Mine Remediation

Stop ongoing AMD treatment

Remediation

Program

Relinquish EPA licence and discontinue:

t = 1

-2 y

ears

t = long term

Program Assessment (Options Paper) & Forward Program

Ongoing Water Treatment Plant Operation and Property Maintenance

‘Remediation of the site that requires no further intervention by, ongoing responsibility for or cost to governmentand / or community’

REM

EDIA

TIO

N P

RO

GR

AM

(long

term

)W

ATER

QU

ALIT

Y PR

OG

RAM

(s

hort

/ med

ium

term

)

2017+

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

t = long term

2007-2011 20012-2015

11

2016

Environmental Audit (Phases 2&3)

Remediation modelDesign features

Long term: Mine remediation

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.

• 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)

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 waste60.5% Waste Rock35.5% Tailings4.0% CaCO3

Dawesley Creek DiversionWater Treatment

Water Quality

Short / medium term: Water Quality

Dawesley Creek Diversion

1.7 km (2004)

260m extension(2014)

Water Treatment – Lime based neutralisation plant

Lime slurry tank Lime/sludgetank Reactor 1

tank

Reactor 2 tank

Thickener12m¢

OUT:

Sludge

(gypsum+metal hydroxides)

OUT: Treated water

Air

Sludge recycling

IN: 75 – 100 kL/h

Acid water (Sulfuric acid + dissolved metals)

Lime AMDpH=2.5

pH=9.5

pH= 9.0 – 9.5

TSS < 10 NTU

High Density Sludge (HDS) Process

Water Treatment & Water Quality - pH

Water Treatment & Water Quality - Cadmium

Water Quality improvements

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Brukunga

Bre

mer

Riv

er

43 km

20 km

<1 km

Dawesley Creek

Mine Site

Langhorne Creek Wine Region

Nairne

Lower lakes

Extent of Historic Contamination1950’s ‐1980’s

Extent of Contamination2004 ‐2014

Extent of Contamination2014+ 

(outside flood events)

With reference to agriculture irrigation & livestock quality standards (ANZECC)

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

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Drilling Technologies for Exploration: (Deep Exploration Technologies CRC / Boart Longyear)

Training (SACOME, TAFE SSA, RTOs) County Fire Services (CFS)

Films & Commercials

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

THANK YOU

Raul MollehuaraProject Director / Operations Brukunga Mine Site

raul.mollehuara@sa.gov.au