Overview of Mine Water Classification

1
Overview of Mine Water Classification its
GenesisDr Bernadette Azzie Golder Associates
Ireland Limited

• Outbursts of Water from the Slovenian Abandoned
  Mines
• 18 March 2010

2
Existing Classifications

• Six major schemes for classifying mine water
  exist
• Facies diagrams (Piper 1944 Durov 1948)
• Glovers scheme (1975)
• Ficklin et al. (1992)
• US Bureau of Mines scheme (1994)
• Youngers scheme (1995)
• Azzies scheme (2000)

3
Piper Diagram
4
Durov Diagram
5
Glovers Scheme

• 1. Acidic with low FeTOTAL conc.
• 2. Acidic with high Fe3 conc.
• 3. Acidic with high Fe2 conc.
• 4. Neutral with high Fe2 conc.
• 5. Suspended ferric hydroxide
• (combined with dissolved Fe2 or Fe3)

6
Ficklin, Plumlee, Smith McHugh
7
US Bureau of Mines Scheme

• GROUP 1
• Net alkaline minewaters
• i.e. alkalinity gt acidity
• GROUP 2
• Net acidic mine waters
• i.e. acidity gt alkalinity

8
Youngers Scheme
9
Azzies Classification

• Basis of Classification
• Geochemical elucidation
• Reflection of factors controlling composition /
  evolution
• Physical response of material surfaces
• Soil colloids, pipes and other metal or concrete
  structures
• Biological response
• Toxicity and salinity

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Azzies Classification

• Selection Criteria
• Alkalinity / acidity (Net)
• Salinity
• I½?mizi2
• Metal ion status
• SAR Na / (Ca2Mg2)½
• or
• AAR (Al3 FeTOTAL) / (Ca2 Mg2)½

11
Azzies Classification
12
Azzies Classification (Refined)
13
Summary

• All classifications are based on geochemical
  attributes
• Waters from some mines exhibit clustering,
  reflecting a geochemical signature which may be
  indicative of processes characterizing water-rock
  interactions in mining.
• Some classifications can be used in engineering
  considerations (e.g. cooling, irrigation)
• Some classifications may be applicable to a wider
  range of aquatic systems.

14
Types of Drainage

• There are 3 types of drainage produced by
  sulphide mineral oxidation

• Neutral Mine Drainage
• Near neutral to alkaline pH
• Low to moderate metals. May have elevated Zn, Cd,
  Mn, Sb, As, or Se
• Low to moderate sulphate
• Treat for metals sometimes sulphate removal

• Saline Drainage
• Neutral to alkaline pH
• Low metals. May have moderate Fe
• Moderate sulphate, magnesium calcium
• Treat for sulphate and sometimes metal removal

• Acid Rock Drainage
• Acidic pH
• Moderate to elevated metals
• Elevated sulphate
• Treat for acid neutralization and metal
  sulphate removal

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What is ML ARD ?

• Metal Leaching Acid Rock Drainage are naturally
  occurring processes.
• ML ARD are caused when metal sulphides come
  into contact with both air and water.
• Rocks at most metal and some coal mines contain
  sulphide minerals.
• Excavating and crushing of ores greatly increases
  amount of rock surfaces which can be exposed to
  oxygen and water.
• So, mining activities can have high potential for
  leaching acid and metals.

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What is ML ARD ?

• ML/ARD can occur from mining wastes (tailings
  waste rock), in an open pit or along underground
  mine surfaces.
• Potential for environmental impacts depends on
• Amount of metals in the mine drainage
• Amount of acid-neutralizing ability in nearby
  rocks water
• Amount of dilution available in streams and
• Sensitivity of the receiving environment.

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Why are ML and ARD important ?

• They can have significant negative impacts on the
  environment if not adequately managed
• High levels of metals and/or acid can be harmful
  or toxic to living organisms
• Metals that are absorbed by plants animals can
  be passed through food chain.
• Once initiated, it can persist for hundreds of
  years until sulphides are completely oxidized,
  and acid and metals are leached from rocks.
• It can be VERY expensive to manage once it has
  developed
• e.g. BC water treatment plants to treat ML/ARD
  have cost gt10million (capital), with further
  1.5million/yr operating cost.

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Mitigation Options 1

• Proper planning of new mining developments can
  reduce risks, liabilities costs associated with
  ML/ARD.
• Geochemical testing of rocks prior to mining can
  predict the likelihood of ML/ARD being an issue.
• Many strategies are available for prevention and
  management of ML/ARD.
• Every strategy has strengths and weaknesses, and
  not all strategies are applicable to all mine
  sites and their environments.
• For best results, a combination of strategies may
  be required.

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Mitigation Options 2

• Basic principle behind management strategies
• Preventing oxygen contact with sulphide minerals
• Reduce amount of water that comes into contact
  with acid generating wastes to minimize the
  amount of leaching.
• Most commonly used strategies include
• Avoidance
• i.e. Dont mine the sulphide-bearing stuff !
• Flooding of mine waste materials
• Timing is crucial
• Covers
• Susceptible to breakdown over time
• Blending of materials
• Only successful on a small scale
• Drainage treatment
• The last resort !

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Mitigation Options 3

• Mitigation strategies must be designed to last
  forever !!
• Mine sites and their environments are dynamic and
  continue to change long after mining has ceased
  .. changes can influence the effectiveness of
  mitigation strategies over time.
• Regular monitoring, maintenance and responsive
  management are key to long-term success in
  preventing impacts from ML/ARD.

21
Case Studies

• Implications of producing large volumes of
  contaminated water can mine water be a
  commodity ?
• e.g. Coal mines in South Africa

22
Background to SA Coal Mining

• Collieries exploiting the Witbank coalfields in
  South Africa have to continuously pump water out
  to reach the coal seams.
• Pyrite occurs naturally in coal formations, and
  when water enters the workings it becomes
  contaminated.
• SA environmental law requires water to be
  suitable for release back into the environment
  (which may involve management and treatment).
• Mines are located in the Upper Olifants
  catchment, which suffers from a chronic water
  shortage.
• Future mining developments are situated
  downstream, as is the scenic Lowveld and Kruger
  National Park.
• Water is characterized by high Ca, Mg and SO4.

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Case Study Irrigation (South Africa)

• Decided to investigate ways in which contaminated
  effluent could become a useful resource.
• Partnership between ACSA, WRC, Univ Pretoria
  Coaltech 2020.
• Natural irrigation water varies greatly in
  quality.
• Some common soil problems that may develop
• Salinity
• Water infiltration rate (?Na ?Ca are
  problematic)
• Specific ion toxicity (Na, Cl, B)
• SACE commissioned three centre-pivot irrigation
  systems, covering 82ha. Aim was to test viability
  of irrigating crops with saline effluent, that is
  high in SO4 and K.

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Case Study Irrigation (South Africa)

• These salts are taken up by certain crops and are
  highly beneficial if managed correctly.
• Irrigation of prime agricultural soils nearby,
  using this water, has improved productivity by
  300.
• Further research required
• Significance of crop selection
• Impact of irrigated salts on soil conditions
• Effects on groundwater
• Significant benefits for small-scale farmers in
  neighboring communities.

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Case Study Treatment (South Africa)

• The Emalahleni Water Reclamation Project sees the
  abstraction and treatment of acidic mine water
  from existing and old mines to a level fit for
  use by the local municipality.
• Sale of the water allows the mining companies
  involved to offset the costs of water treatment.
• In 2005, the local municipality was drawing
  80-90MLD from Witbank Dam, but this was 20MLD
  short of that required.
• A 0.120MLD demonstration plant was built and run
  for 3 months.

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Case Study Treatment (South Africa)

• Results from the demonstration plant indicated
  that
• pH increased from 2.9 to 7.
• Total dissolved solids concentration reduced from
  4500mg/L to 135mg/L.
• SO4 concentrations reduced from 3500mg/L to
  80mg/L.
• A yield of 98 was achieved.
• Treated water meets SABS 241 Class 0 Drinking
  Water Quality Limit.
• A full scale plant (20MLD) was commissioned in
  2007, and is now fully operational.
• The full scale plant draws water from 3 mines,
  conveys it to a storage facility at treatment
  site.
• Storage facility has capacity for 46MLD, so
  caters for seasonal fluctuations.

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Case Study Treatment (South Africa)

• Acid water first undergoes neutralization using
  lime/ limestone.
• This increases pH and allows metals to
  precipitate out.
• Following clarification water is treated using
  ultrafiltration to remove remaining metals
  bacteria.
• Reverse osmosis using spiral membranes then
  removes remaining salinity.
• 500 UF membranes and 1200 RO membranes are being
  used.

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Case Study Treatment (South Africa)

• Treated water is stored in 10MLD dome-shaped
  concrete reservoirs before being pumped 9km to
  the municipal reservoir for distribution to
  consumers.
• Approx 100m3/day of brine and 100t/day
  gypsiferous waste is produced.
• Brine is disposed of in 330,000m3 evaporation
  ponds.
• An on-site laboratory monitors water quality.

29
Case Studies

• Geochemistry to show impact of abandonment and
  rehabilitation
• e.g. Coal mine in South Africa Pb-Zn mine in
  Ireland

30
Case Study TNDBC (South Africa)
Surface subsidence
Burning u/g workings
AMD
Polluted river
31
Case Study Silvermines (Ireland)

• The Silvermines Rehabilitation Project involves
  rehabilitation works on 6 sites in the
  Silvermines area with expenditure of some 10.6m
  over a 4-year period.
• The Tailings Management Facility (TMF) for the
  mine is at Gortmore, approximately 5km to the
  west of Silvermines village.
• The rehabilitation of the Gortmore TMF is wholly
  or mainly necessary for the purpose of public and
  animal health and safety, for the protection of
  the environment and in the public interest.

32
Case Study Silvermines (Ireland)

• Rehabilitation essentially involves the
  establishment of a self-sustaining cover on the
  TMF, improvement of existing surface water,
  groundwater and stream sediment quality,
  landscaping and ancillary engineering works
  related to the TMF decanting system, wetlands and
  settlement ponds.

33
Case Study Silvermines (Ireland)
Gortmore TMF
34
Case Study Silvermines (Ireland)

• Tailings range in thickness from 8 10m.
• TMF overlies a layer of native overburden
  (alluvium glacial till) which is 2.2m 8.7m
  thick.
• Overburden is underlain by Ballysteen Formation
  (limestone).
• In the TMF, there is a thin crust of oxidized
  tailings overlying very soft grey unoxidized
  tailings.
• The crust varies from 10cm thick in the centre,
  to 1m thick at the edges of the TMF.
• Slopes are presently stable.

Geotechnical investigation
35
Case Study Silvermines (Ireland)

• Water table is 1-2m below tailings surface, with
  a pool in the centre of the surface.
• Downward vertical gradients observed in
  boreholes, with downward seepage within and along
  dam walls.
• Seeps observed along external toe of dam.
• There is little/no hydraulic gradient between
  overburden and underlying bedrock.
• Slight horizontal hydraulic gradient from NE to
  SW in upper 15m of underlying bedrock.

Hydrogeology
36
Case Study Silvermines (Ireland)

• Areas of bare tailings are characterized by low
  pH, high EC, SO4 and heavy metal content.
• Vegetation (poor grassland) samples showed
  elevated SO4, Pb, Zn, Cd, Mn and Zn, sometimes
  above toxicity levels.
• Tailings samples in bare patches show potential
  for acid generation.
• Upward movement of acidity and phytotoxic metal
  and sulphate salts has severely impacted on
  vegetation sustainability in poor grassland areas.

Tailings Vegetation
37
Case Study Silvermines (Ireland)

• Wetlands around TMF are removing suspended solids
  and metals from surface water and seepages.
• Settlement ponds are not functioning effectively.
• Wetlands and settlement ponds are to be
  refurbished as part of remediation process.
• There are numerous uncontrolled seepages into the
  Kilmastulla River.
• However, metal concentrations downstream in river
  are within ranges of relevant standards.
• River has Q3-4 rating (stable)

Surface Water Quality
38
Case Study Silvermines (Ireland)

• Boreholes were drilled on tailings dam surface
  and close to toe of the dam wall.
• Similar values for metals and sulphate
  concentrations were found in samples taken in
  2001 and 2006.
• Previous studies found no evidence of groundwater
  contamination at any potential receptor.

Groundwater Quality
39
Case Study Silvermines (Ireland)

• Metals were found in river sediments alongside
  the TMF.
• These are probably due to many uncontrolled seeps
  and drains which wash sediment into the river,
  especially during periods of high rainfall.
• Proposed improvements to the wetlands will
  significantly reduce sediment loading on the
  river.

Stream sediments
40
Case Study Silvermines (Ireland)

• Identified total area for capping is 24.5ha.
• Treatment of embankment slopes will also be
  carried out to cover potentially acid generating
  materials and/or buttress toe slopes.
• Rock fill will be used on slopes requiring
  treatment.

Capping System I
41
Case Study Silvermines (Ireland)
Capping System II

• Principal elements of recommended capping design
  include
• 200mm layer (min) of growth medium, together with
  suitable seeding mixture.
• Geosynthetic layer
• 300mm layer (average) of granular non-acid
  generating crushed stone (rock fill) ? capillary
  break
• Geosynthetic layer
• Total thickness of capping system is 0.5m.
• A grass seed mix will be used. Seeding will be at
  upper end of 150-200kg/ha rate for vegetation of
  mine wastes.

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Closure Objectives

• Main closure objectives include
• Physical stability
• Chemical stability
• Biological stability
• Hydrological hydrogeological environment
• Geographical and climatic influences
• Local sensitivities and opportunities
• Successive land use
• Funds for closure
• Socio-economic considerations

43
Criteria for Mine Closure

• Closure plans
• Costs included in the assessment of alternatives
• Adopt a risk assessment approach
• Are developed in Mine Planning phase
• Should be maintained during active life of a
  facility, and routinely updated when
  modifications are made
• Facilities to be designed to facilitate premature
  closure
• After-care design should minimize the need for
  active management

44
Case Study New Largo (South Africa)
Does this qualify for a closure certificate ?