ML/ARD Impacts and Rehabilitation Planning for Rum Jungle

November 28th, 2018 25th MEND ML/ARD Workshop

Paul Ferguson1, Christoph Wels1, David Jones2, Graham Farrer3

1Robertson GeoConsultants Inc. 2DR Jones Environmental Excellence

3NT Department of Primary Industry and Resources

Overview

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o  Focus: “what happened, what was unexpected and future objectives”

o  Initial rehabilitation in the 1980s •  Works completed •  Performance •  Current site conditions

o  Future rehabilitation plan •  Preferred rehabilitation strategy •  Predicted performance

o  Summary and Path Forward

Site Location and Physical Setting

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Darwin

Rum Jungle Fog Bay (Finniss River)

Browns (C&M)

Rum Jungle

Markich and Jeffree (2002), The Finniss River: A Natural Laboratory of Mining Impacts – Past, Present, and Future, ANSTO E/748.

East Branch of Finniss River (no biota in 1960s and 1970s)

15 km

Timeline for Mining and Rehabilitation

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1949 Discovery of uranium

Active mining

1953 to 1971

1971 Site abandoned

1983 to 1985 Rum Jungle Rehabilitation Project (AU$16.2M)

2010 Rehabilitation planning re-commences

1986 to 1998 Monitoring Rehab /

•  Uranium (for CDA) •  Cu, Ni, and Co

Planning/C&M

1977 Limited rehabilitation

Historic Site Layout (1970s) – Prior to Rehabilitation

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Main WRD

Main Pit

Dyson’s Pit

Old Tailings Dam

Intermediate Pit

East Branch of the Finniss River (EBFR)

Dyson’s WRD

Intermediate WRD

Heap leach pile

Diversion channel

Mill

Post-Rehabilitation (Current) Site Layout

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pH 7 to 8 SO4 500 to 1,500 mg/L Low concentrations of Cu, Co, Ni, and Zn

Dyson’s Pit (backfilled)

Main WRD

(covered)

Dyson’s WRD (covered)

Int. WRD (covered)

Browns Pit

‘Old Tailings Dam’ area (tailings re-located to Dyson’s Pit)

Int. Pit (limed)

Main Pit (treated)

Former heap leach pile (spent material to Dyson’s Pit)

Rehabilitation Objectives (1983): 1.   Achieve drinking water guidelines in EBFR 2.   Reduce public health hazards (from radiation) 3.   Improve site aesthetics, including re-vegetation

EBFR (Monitoring Station)

EFDC (90% of flows)

10%

Pre-Rehabilitation Conditions

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Copper heap leach pile, August 1984 Old Tailings Dam, June 1983

Main (White’s) WRD, June 1983 Intermediate WRD, January 1985

Post-Rehabilitation Conditions

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Copper heap leach pad, August 1986 Old Tailings Dam, May 1986

Main (White’s) WRD, May 1985 Intermediate WRD, May 1986

Current Site Conditions

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Main WRD and Fitch Creek Dyson’s Area

Intermediate WRD and EFDC

Conceptual cross-section, Dyson’s (backfilled) Pit

Vegetation Community Map (from EcoLogical, 2014)

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Invasive grasses, e.g. Gamba (Units 12 to 19, in orange)

Copper Concentrations in EBFR Downstream

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Before initial rehabilitation in 1984/1985

8.8

1988 to 1998 2009 to 2015 Post-rehabilitation

0.09

Dissolved Copper Concentrations in EBFR, 2009 to 2015

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60 µg/L (LDWQO)

1500 µg/L (drinking water)

Locally Derived Water Quality Objectives (LDWQOs)

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60 µg/L Cu

28 µg/L Cu

8 µg/L Cu

4 µg/L Cu Not shown: SO4, Al, Co, Fe, Mg, Mn, Ni and Zn

From Hydrobiology (2015)

Test Pitting – WRD and Contaminated Areas

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Preferred Rehabilitation Strategy

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Existing tailings

60% PAF-I

40% PAF-II

18% PAF-II

32% PAF-III

16% Soils

34% NAF

7.1 Mt (New WSF)

4 Mt (Main Pit)

From O’Kane Consultants (2016)

Conceptual Waste Storage Facility (WSF) Design

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Main Pit (backfilled)

From O’Kane Consultants (2016)

3.5 m thick

MODFLOW/MT3D Model Domain and Boundary Conditions

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Simulated Contaminant Plumes (Pre-Rehabilitation), 1984

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Dyson’s WRD

Main WRD

Intermediate WRD

Dyson’s Pit

Former heap leach area

Old Tailings Dam area

Browns Pit

Former plant (ore stockpile)

Sulfate, mg/L

Copper, mg/L

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Simulated Contaminant Plumes (Current Conditions), 2015

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Dyson’s WRD

Main WRD

Intermediate WRD

Dyson’s (backfilled )

Pit

Former heap leach area

Old Tailings Dam area

Browns Pit

Former plant (ore stockpile)

Sulfate, mg/L

Copper, mg/L

Predicted Contaminant Plumes (Post-Rehabilitation), 2045

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Backfilled Pit

New WSF

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Residual Copper Plumes Sulfate, mg/L

0

500

1000

1500

2000

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since rehabilitation, years 0

200

400

600

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since Rehabilitation (yr)

0

200

400

600

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since Rehabilitation (yr)

0

200

400

600

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since rehabilitation, years

0

200

400

600

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since rehabilitation, years

0

200

400

600

0 10 20 30

SO4 L

oad,

t/ye

ar

Time since rehabilitation, years

Total Flux to EBFR (All Reaches)

419 t/year SO4 (-71%)

Predicted Sulfate Loads to EBFR

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Predicted Copper Loads to EBFR

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0.000

0.005

0.010

0.015

0.020

0 5 10 15 20 25 30

Cop

per L

oad

(Flu

x), t

/yea

r

Time since rehabilitation, years

Predicted Copper Concentrations in EBFR

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Before initial rehabilitation in 1984/1985

8.8

Post-rehabilitation (current site configuration)

0.09

0.008 Predicted (30 years post-rehab)

Path Forward

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o  DPIR (the ‘Proponent’) intends to submit an EIS to NT EPA by mid-2019 and Detailed Business Case (DBC) by end of 2019

o  Refinements being considered (Stage 2A): •  Main Pit configuration: (i) covered landform or (ii) flooded above backfill. •  New WSF location: (i) northern or (ii) central location). •  Post-rehab seepage (SD) management: WTP, MNA, and/or passive options.

o  Other issues to be addressed: •  Re-vegetation treatments and weed management •  Borrow area and haul road disturbances (on Finniss River Land Trust)

o  Each refinement/issue has environmental and social implications that require Traditional Owner (TO) input.

o  Financial and liability implications for Commonwealth Government of Australia must also be considered in NT’s DBC.

Questions/Comments

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