A guide to leading practice sustainable development in mining

Figure 5.19 - Rehabilitated mine site in 2005, following construction of cover
over the waste rock pile.
Ideally the closure phase will consist largely of the last stages of decommissioning,
including demolition of infrastructure, final land-forming, revegetation and
commencement of a post-closure monitoring program.
Since AMD issues can have a long lag time before they become evident, it may
be necessary to monitor the success of revegetation, the effectiveness of cover
systems, and any impacts on water resources for many years until good evidence of
stability is on hand and sign off can be obtained from the regulator.
It should be remembered that many of the AMD management technologies
are still relatively new (less than 30 years old) so there are very few long term
benchmarks of success in achieving environmentally safe and stable landforms. The
long term performance of closure measures needs to be demonstrated, initially
through techniques such as modelling, but will always need to be verified through
achievement in the field. Companies should be prepared to monitor for a long time
after closure where AMD risks and potential consequences are judged to be high.
Such a responsible approach will enhance the reputation of the industry and help to
maintain its social licence to operate. Closure issues are dealt with comprehensively
in the Leading Practice Sustainable Development handbook on “Mine Closure and
Completion.”
Water covers
The most effective way of restricting the exposure of reactive wastes to oxygen is
to deposit them permanently under water, a technique that succeeds because of the
limited amount of dissolved oxygen in water. However, water covers are only viable
when an assured supply or storage of water is available.
For surface reactive waste storages, this will require valley containment in a catchment
of sufficient size to maintain a water cover over the wastes, incorporating a water dam
and spillway. This normally requires a net positive water balance climate, generally
A GUIDE TO LEADING PRACTICE SUSTAINABLE DEVELOPMENT IN MINING 155