Rehabilitation of Open Pit Mines

M i n i n g P h i l i p p i n e s 2 0 1 0

bmp R e h a b i l i t a t i o n o f O p e n P i t M i n e s

R E H A B I L I T A T I O N

O F O P E N P I T

M I N E S

bmp Environment & Community Care, Inc.

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R e h a b i l i t a t i o n o f O p e n P i t M i n e s

Rapu-Rapu Minerals, Inc.’s Open Pit

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R e h a b i l i t a t i o n o f O p e n P i t M i n e s bmp



Overv iew o f the

Presen ta t ion

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1. Adverse Impacts of Open Pit Mining at

Mine Closure

2. The Philippine Policy on Open Pit Mine

Rehabilitation

3. The State of the Art of Open Pit Mine

Rehabilitation

4. Challenges for Philippine Open Pit

Mines

Overview of the Presentation

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Adverse Impac ts o f

Open P i t M in ing a t

Mine C losure

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“Open pit mining wreaks havoc to the

environment; not only does it deforest, it

also leaves wildlife homeless, and erodes

the soil which upland communities and

lowland farmers depend on for their

livelihoods” (HARIBON, www.indcatholicnews.com).

Adverse Impacts of Open Pit Mining at Mine Closure

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Onsite environmental

impacts

1. Physical – Change in

landform; pit wall

instability; creation of pit

lakes

2. Chemical – Metals;

metalloids, AMD

3. Biodiversity – Loss of

vegetation and wildlife/

aquatic habitats

4. Aesthetics

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(Castendyk and Eary, 2009)

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Downstream environmental impacts

1. Surface and groundwater contamination

2. Biodiversity – River corridor, coastal, and near-

coast

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Social impacts

1. Resettlement

2. Livelihood impacts – agriculture and fisheries

3. Loss of cultural/recreation sites

4. Public safety and health impacts


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The Ph i l i pp ine Po l i cy

on Open P i t M ine

Rehab i l i ta t ion

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Classified as “environmentally critical”, open pit

mining projects need an ECC prior to

development. An ECC is a document issued

by the DENR after a positive review of the

project’s EIA. It certifies that, based on the

representations of the proponent and the

commitment to implement the approved

Environmental Management Plan (EMP), the

proposed project will not cause significant

environmental impacts.

The Philippine Policy on Open Pit Mine

Rehabilitation

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The DENR requires the inclusion of “policies

and generic procedures” on mine

decommissioning and rehabilitation in the

EMP. The detailed activities, timetable, and

costs are to be provided in the Final Mine

Rehabilitation and Decommissioning Plan

(FMRDP) which will be submitted after the

grant of ECC prior to project construction.


Rehabilitation

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The FMRDP Guidelines of the MGB prescribe

as one of two specific goals:

“To prevent or eliminate long-term

environmental impacts by returning mining-

disturbed land to a physically and chemically

stable, visually acceptable, productive or self-

sustaining condition, taking into consideration

the beneficial uses of the land and the

surrounding areas and as agreed with

stakeholders.”


Rehabilitation

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“Physically stable shall mean that the mine

component does not pose a hazard to public

health and safety as a result of failure or

physical deterioration … it should not erode or

move from its intended location under the

extreme events or perpetual disruptive forces

to which it will be subjected after closure.”


Rehabilitation

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“Chemically stable shall mean that a mine

component should not release chemicals

(contaminants) into the environment. Using

proven techniques, the production of

contaminants should be controlled at source

using a system of containment, collection, and

treatment systems in order to meet regulatory

standards. However, the use of effluent-

treatment facilities should not be considered as

rehabilitation but a temporary measure …


Rehabilitation

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Stakeholder involvement is crucial to the

preparation of the FMRDP. This is to ensure

that their interests, concerns, and local

knowledge are considered in the Plan.


Rehabilitation

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Once the FMRDP is approved by the MGB, its

total cost becomes the Final Mine

Rehabilitation and Decommissioning Fund.

The mining company makes annual deposits

on the Fund based on a formula such that the

full amount is accrued a year before mine

closure.


Rehabilitation

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The State of the Ar t

of Open Pi t Mine

Rehabi l i ta t ion

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State-of-the-art open pit mine rehabilitation

acknowledges that assuring good water quality

of pit lakes poses the greatest challenge.

State of the Art of Open Pit Mine Rehabilitation

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Facing up to this challenge entails three

interrelated planning tasks:

1. Evaluation of the likely water quality of pit lakes

after mine closure

2. Formulation of any long-term mitigation

program and

3. Evaluation of the lake’s social or environmental

beneficial end uses.


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Pit lake water quality is a function of

hydrologic, biogeochemical, geologic, and

limnologic processes (Castendyk and Eary,

2009).


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(Castendyk and Eary, 2009)

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Mitigation program (Eary and Castendyk,

2009):

1. Prefilling – Backfilling, perpetual pumping, wall-

rock covers, runoff collection, excavation of

reactive material, expansion of the littoral zone

2. During filling – Density-driven meromixis,

surface water flooding

3. Postfilling – In situ chemical treatment,

biochemical treatment, structurally imposed

meromixis, discharge management


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(McCullough, Hunt, and Evans, 2009)

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Examples of post-mining end uses of pit lakes

(McCullough, Hunt, and Evans, 2009):

1. Recreation and tourism

2. Wildlife conservation

3. Aquaculture

4. Irrigation

5. Potable water

6. Industrial water

7. Chemical extraction

8. Educational facility


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Pit wall geotechnical stability after closure is

influenced by (Van Zyl, 2009):

1. Hydrogeological changes

2. Stress relief or relaxation

3. Shear strength changes of pit wall materials


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A better understanding of the long-term

behavior of jointed rock masses after

unloading, analysis of pit walls following

closure, and analysis of the effects of large

failures on wave development and dissipation

in pit lakes are needed. Currently, not much

attention is being given to these areas (Van

Zyl, 2009).


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Major activities of open pit mine rehabilitation:

1. Removal of structures, wastes, PAF materials

2. Earthworks, recontouring, and revegetation

3. Lake filling


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Chal lenges for

Phi l ipp ine Open Pi t

Mines

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The burden is on open pit mines to show that

the depleted pit wall and pit lake do not

become long-term liabilities. Instead, they are

developed for social, economic, and

environmental end uses.

Challenges for Philippine Open Pit Mines

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No less than a concerted government-industry-

consultancy-academic effort is required.


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Areas of collaboration:

1. Use of predictive models to evaluate potential

impacts to water quantity and quality of pit

lakes. A range of likely outcomes can be

determined on which risk assessment and

management should be based.

2. Collection and dissemination of observations of

pit lake water quality over time from a variety of

geologic and climatic settings. The data can be

used to validate the model predictions.


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Areas of collaboration:

3. Research on the postclosure stability of open

pits and inclusion of slope stability

considerations in the FMRDP.

4. Use of community-based benefit-cost studies

for the open pit during the EIA.
