Mine Rehabilitation at Yerranderie

Location of Yerranderie

• 100 km southwest of Sydney

• Special Area within Warragamba catchment (Schedule 2 lands) and close to the Kanangra Boyd Wilderness Area

• Headwaters of the Tonalli River – water travels 12km through protected bushland into Lake Burragorang

Location of Tonalli River and Yerranderie Derelict Silver

Mining Field N

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0 km 1

Scale

Tonalli River

Lake Burragorang

Yerranderie Silver Mining Field

Yerranderie Timeline

1899-1906 mining 1st grade ore1906-1912 processing plants: crushing ore1912-1915 small mines operated1920s six major mines operated1929-1930 Labour dispute lead to closure of

large scale mining1942-1960 Warragamba Dam built, access to

Yerranderie not available from the East, Yerranderie became a remote site

1940-1980 limited mining and site left as derelict mining field

Water Quality Issues

• Large mounds of processed tailings• Minimal run-off controls from

processing site• Metal contamination above

acceptable levels• Metals of concern include

– Copper– Lead– Zinc

• Aquatic ecosystems within and immediately downstream potentially compromised

Water Quality Issues

• Erosion and lack of vegetation lead directly to environmental problems

• Sediments eroding from processing sites and washing into Tonalli River

Water Quality Issues

• Crushing ore reduced grain size, increasing surface area exposed to air and the potential of erosion

• Exposure to air and water – potential for Acid Mine Drainage through oxidisation of sulfur in Pyrites (Sulfuric Acid) and the release of metals in low pH conditions

Who is responsible for rehabilitation works?

Significant collaboration required between stakeholders/partners:

• Private landholders• Sydney Catchment Authority• NSW National Parks and Wildlife Service (now

Department of Environment and Conservation)• NSW Department of Primary Industries –

Mineral Resources• NSW Department of Land and Water

Conservation (now Department of Lands)

Yerranderie Derelict Silver Mining Field

• Over 200 adits, shafts, tunnels and trenches in an area over 10 km square

• Underground mining methods used

• Ore brought to surface

• Most material on surface is 2nd grade ore = high in sulfides

Rehabilitation Aims

• Contain processing tailings and contaminated sediment

• Reduce sediment transport to the Tonalli River

• Detain runoff and redirect clean waters around the processing sites

• Minimum impact on the environment and cultural heritage of the area

Understanding the Yerranderie site

Field StudiesGeology, soil,

topography, climate, flora, fauna, heritage

Why?To ascertain potential

impacts of remedial work

To consider long term implications of actions and allow for further works later

Minimise Negative Impacts

Yerranderie mine rehabilitation strategy counters potential impacts by including protection measures for:

1. Soil erosion and water quality

2. Flora and fauna 3. Heritage

Rehabilitation Choices for Yerranderie

Alternative actions considered

• Onsite burial of processed material

• Remove material to another site or a single processing area

• Soil conservation works• Reprocessing of tailing

material• Complete site remediation• Do nothing: no proactive

action – allow tailings to erode ‘naturally’

Soil Conservation Works

• Aim to divert clean water around contaminated sites and capture contaminated water and tailings

• This option chosen as it has– Limited damage to heritage items– Reduced risk of groundwater and

surface water contamination– Reduce further pollution potential

Four Major Sites Chosen for Rehabilitation

1. Silver Peaks Processing Area

2. Colon Peaks Processing Area

3. West of Wollondilly Mine Processing Area

4. Kerrys Shaft Processing Area

Silver Peaks Processing Area

What happened?• Built earth diversion bank above processing site

and a sediment containment pond below the processing area

Why?• To divert clean water around the contaminated

sediments. Water enters a stilling basin to reduce flow velocity and erosion

What did it achieve?• Processing area catchment, water volumes,

velocity and overal sediment movement into constructed dam greatly reduced

Silver Peaks Works – Lower Dam

Before work

After work

Runoff captured in Dam

Silver Peaks Works

Clean water diversion bank – before and after works

Kerrys Shaft – Lower Dam

During construction

After work water capture

Before work

Outcomes of the Rehabilitation Works

• Water quality results from captured water in dams– poor quality– low pH– elevated metal levels especially for Silver Peaks– sediment captured

• Detention of tailings runoff in catch ponds is reducing the sediment an poor water quality moving downstream

• Rehabilitation works have a positive effect on water quality and ecology downstream

Analyte Kerry Shaft Dam

Silver Peaks Dam Colon Peaks Dam

ANZECC 2000 95% Trigger Levels

Total Copper ug/L

12 N/A 62 1.4

Total Lead ug/L

N/A 1550 1360 3.4

Total Silver ug/L

<1 3 4 0.05

Total Zinc ug/L

5200 54800 11100 8

Analyte Kerry Shaft Dam

Silver Peaks Dam Colon Peaks Dam

ANZECC 2000 95% Trigger Levels (for slightly disturbed ecosystems)

pH 7.7 2.8 6.3 6.5 -7.5

Electrical Conductivity uS/m

480 1345 680 30-350

Total Copper ug/L

12 5010 8 1.4

Total Lead ug/L

28 1120 32 3.4

Total Silver ug/L

1 16 <1 0.05

Total Zinc ug/L

3060 50700 3990 8

Results December 2000

Water Quality Monitoring Results: July 2000

Ongoing Monitoring and Further Works

• Development of a comprehensive Rehabilitation Action Plan for the Yerranderie Mine Area

• Awarded Environmental Trust Grant: $631,000 provided by NSW Government for 3 years of work

• Longer term studies of mines– Water quality monitoring program on Tonalli River– Flora/Fauna studies, especially of bat habitat in mine

shafts– Metallurgical Study on feasibility of reprocessed

tailings– Aboriginal/Non-Aboriginal Heritage Study– Risk assessment of all mine sites for public safety

Photography Credits

All photographs in this presentation are reproduced with kind permission of the copyright owner: Sydney Catchment Authority.