Environmental Engineering Reference
In-Depth Information
10. Pit Wall Acid Rock Drainage - ARD from the pit wall prevents vegetation from
establishing and is usually the main source of poor quality water draining into the pit.
If necessary, steps can be taken to minimize this source by covering or inundating areas
of potential acid generation.
11. Final Void Abandonment Bund - this is to prevent inadvertent access to the pit area
and should be designed in accordance with the following:
● The location is based on an evaluation of the long-term stability of the pit walls.
In the absence of dei nitive slope stability studies, it should be assumed that, in the
long-term, the slopes will fail back to an angle of 37ΒΊ from the toe. The bund should
be located beyond this notional i nal crest.
● The bund, in conjunction with the vegetation grown on it, will provide a screen,
shielding the pit walls from view, and
● The bund proi le should be such that it prevents vehicular access and deters pedes-
trian access.
Soil Preparation and Use of Topsoil
Much has been written about the salvage, storage and re-use of topsoil in mine land
rehabilitation. Some advocates claim that the benei ts of using natural topsoil are so
overwhelming that its use should be mandatory. Others claim that the benei ts are not jus-
tii ed by the costs, and that artii cial soils can be produced that provide the same or bet-
ter conditions for plant growth. Examples can be found to support either case. However,
it is probably true that increasing recognition of topsoil as a valuable resource (a concept
that resonates with the mining industry) has resulted in its use on most projects devel-
oped during the past decade. However, there are examples of successful projects where
It is probably true that increasing
recognition of topsoil as a
valuable resource (a concept
that resonates with the mining
industry) has resulted in its use
on most projects developed
during the past decade.
CASE 21.3
Flooding of the Island Copper Mine Pit
The Island Copper Mine Pit near Port Hardy, Vancouver
Island, BC, Canada, was fl ooded in 1996 with seawater
and capped with fresh water to form a meromictic (per-
manently stratifi ed) pit lake of maximum depth 350 m
and surface area of about 1.7 km 2 . The pit lake is being
developed as a passive treatment system for acid rock
drainage (ARD). The physical structure and water quality
has developed into three distinct layers: a brackish and
well mixed upper layer; a plume stirred intermediate layer;
and a thermally convecting lower layer. To date the upper
halocline has risen due to the injection of buoyant acid
rock drainage (ARD) into the base of the intermediate
layer. An upper layer 'equilibrium' depth is expected in the
near future refl ecting a balance between meteorological
forcing from above and rising ARD plumes from below. The
lower halocline depth fl uctuates seasonally: deepening
in the winter due to high ARD fl ows, which erode the
lower halocline; and rising in the summer when thermal
convection in the lower layer dominates over reduced
intermediate layer stirring. The proposed treatment of
acid rock drainage by metal-sulphide precipitation using
sulphate-reducing bacteria is dependent on anoxia develop-
ing in the intermediate and lower layers. The major issues
facing the passive treatment system are developing and
maintaining anoxia in the intermediate layer and maintain-
ing meromixis.
Source: Fisher and Lawrence 2006
Photo Credit: www.minemosaic.com
 
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