Rehabilitation of Open Pit Mines

Mining Philippines 2010

REHABILITATION
OF OPEN PIT
MINES

bmp Environment & Community Care, Inc.

bmp Rehabilitation of Open Pit Mines


Rapu-Rapu Minerals, Inc.’s Open Pit



Overview of the
Presentation



Overview of the Presentation

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



Adverse Impacts of
Open Pit Mining at
Mine Closure



Adverse Impacts of Open Pit Mining at Mine Closure

“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).



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



(Castendyk and Eary, 2009)



Downstream environmental impacts
1. Surface and groundwater contamination
2. Biodiversity – River corridor, coastal, and near-
coast




Social impacts
1. Resettlement
2. Livelihood impacts – agriculture and fisheries
3. Loss of cultural/recreation sites
4. Public safety and health impacts



The Philippine Policy
on Open Pit Mine
Rehabilitation



The Philippine Policy on Open Pit Mine
Rehabilitation
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.


Rehabilitation
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
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
“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
“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
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
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.



The State of the Art
of Open Pit Mine
Rehabilitation



State of the Art of Open Pit Mine Rehabilitation

State-of-the-art open pit mine rehabilitation
acknowledges that assuring good water quality
of pit lakes poses the greatest challenge.




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.



Pit lake water quality is a function of
hydrologic, biogeochemical, geologic, and
limnologic processes (Castendyk and Eary,
2009).




(Castendyk and Eary, 2009)



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




(McCullough, Hunt, and Evans, 2009)




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



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




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).




Major activities of open pit mine rehabilitation:
1. Removal of structures, wastes, PAF materials
2. Earthworks, recontouring, and revegetation
3. Lake filling



Challenges for
Philippine Open Pit
Mines



Challenges for Philippine Open Pit Mines
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.




No less than a concerted government-industry-
consultancy-academic effort is required.




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.




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.


Rehabilitation of Open Pit Mines

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