Environmental Engineering Reference
In-Depth Information
It has been argued that following completion of mining, the aquatic ecosystem within the
lake can be re-established by raising the bottom of the lake with tailings i ll, and raising the
water cover over the top of the tailings with fresh or treated water (Frazer and Robertson
1994; Sly 1996; Robertson 1998). This, so it is said, effectively creates a 'natural design' at clo-
sure, which allows sunlight to penetrate to the lake bed, where previously it did not. Such
'enhanced natural design' further allows plants in the lake to produce oxygen, improving the
biology and i shery of the lake. While the sub-aqueous disposal of tailings to natural water
bodies is appealing, the actual circumstances where this may be acceptable are probably
uncommon, and some of the potential environmental consequences are not fully understood.
The application of sub-aqueous underwater tailings placement in natural water bodies
is a relatively common practice in Canada, a leading mining nation. In the past decade, six
mines have been approved and i sheries compensation measures implemented at Canadian
mine sites, which have been successful in restoring i sheries and wetlands habitat. Examples
include: the Kemess Mine and Benson Lake in British Columbia, Buttle Lake on Vancouver
Island, and Mandy and Anderson Lakes in Manitoba ( www.trustingold.com ). Canada has
also successfully employed this technology to mitigate the potential impacts of acid rock
drainage from reactive waste rock by placing the material under water.
Submarine Tailings Discharge
Marine discharge of tailings has been carried out at many sites, and has varied between shore-
line disposal and discharge at great depths. The most recent and most successful examples use
what is termed Deep Sea Tailings Placement (DSTP), which involves discharge of tailings
slurry at the seabed in water depths of 100 m or more, with the tailings slurry l owing down the
seabed slope as a density current before depositing on the seabed at depths of 400 m or more.
Unfavourable terrestrial conditions, such as a steep terrain combined with high rain-
fall and seismic activities, characteristic for countries such as the Philippines or Indonesia,
may lead to unacceptable risks in case of on-land TSF and submarine tailings disposal may
become the preferred option.
Unfavourable terrestrial
conditions, such as a steep
terrain combined with high
rainfall and seismic activities, may
lead to unacceptable risks in case
of on-land TSF and submarine
tailings disposal may become the
preferred option.
18.3 SURFACE TAILINGS STORAGE
Traditionally, tailings management has used surface impoundments to retain tailings and
mill efl uent. This practice in the USA is supported by the 1982 USEPA research report:
Development Document for Efl uent Limitations Guidelines and Standards for Ore Mining and
Dressing - Point Source Category . In this document USEPA proi les a variety of mining
sources (gold, silver, copper and molybdenum mines, etc.) regulated under the Clean Water
Act, discusses New Source Performance Standards, and outlines Best Available Treatment
and efl uent limitation guidelines. In the USA this document remains the basis for designat-
ing tailings ponds and settling/treatment as best available treatment technology. The factors
that inl uence design and operation of a TSF include: (1) general design criteria, (2) tailings
pulp density, (3) types of layouts, (4) embankment design, (4) tailings discharge, (5) common
water discharge systems, (6) operation consideration, (7) water balance, (8) site selection,
(9) site investigation, (10) risks, (11) monitoring, (12) auditing, and (13) TSF closure.
General Design Criteria
The design approach and safety requirements for tailings embankments are often adapted
from the practice of conventional dam engineering and a wealth of knowledge exists.
 
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