Erosion - Mining and the Environment: From Ore to Metal - page 796

mitigating dust, can trigger other environmental consequences. For instance, in areas
where water is a scarce resource, water for dust suppression competes with other needs
for water. There are other potential environmental consequences resulting from the over-
application of water that must be considered. These include runoff problems, soil insta-
bility, spreading of contaminants in the environment (for example, oil from engines), and
water erosion. The over-application of water can also lead to transport problems if the
wetted surface becomes slippery or boggy. Chloride salts also need to be used with care.
Magnesium chloride used for dust control in the USA has been implicated in the death
of pine trees located immediately downslope of the sites of application. It is important to
keep these environmental consequences in mind when deciding on the extent to which
water and chemical dust suppressants are to be used.
Stabilization of disturbed sites upon completion of earthworks is important. Disturbed
soil may be compacted with rollers or other similar equipment in order to reduce the ero-
sion potential of the area. With time, however, disturbed land areas need to be stabilized
through revegetation. Although the main objective of revegetation in wet climates is to
reduce water erosion, reducing wind erosion is also important.
As a rule of thumb, surfaces of completed earthworks (including landscaping) should
be re-vegetated (i.e. seeded and mulched) within one or two weeks after active operations
have ceased. Groundcover should be of sufi cient density to expose less than one-third
of un-stabilized ground within two to three months of planting, and all times thereafter
(Cheminfo Services 2005). Restoration control measures should be maintained and reap-
plied, if necessary. The area should be restored such that the vegetative groundcover
and soil characteristics are similar to adjacent or nearby undisturbed native conditions.
Reseeding using native grasses is prudent. Care must be taken to avoid introducing or
promoting the spread of noxious weeds and plants or those foreign to the area (see also
Chapter Twenty-One on mine closure).
Temporary seeding and mulching may be applied to cover bare soil and to prevent
wind erosion. The soil must be kept moist to establish cover. Mulch can protect the soil
surface until newly seeded vegetation can take over and improves the chance of rapidly
establishing a dense grass stand. Some types of mulch require tilling to integrate them into
the upper layer of soil, if they are to be effective in dust control. Light mulches, such as
straw, should be tacked in place, either mechanically or by application of a chemical tack-
ing agent. Areas may need to be reseeded, so that a stabilized surface is formed within
eight months of the initial application.
Vegetation belts can provide extra protection against wind erosion reducing the wind
velocity for distances up to 30 times the height of the vegetation. Vegetation grown on and
around strategic locations to mitigate fugitive dust emissions may consist of scrubs, bushes,
or trees in one to ten rows. One, two, three and i ve-row barriers of trees are found to be
the most effective arrangement for planting to control wind erosion (Cheminfo Services
2005). The type of tree species planted also has considerable inl uence on the effectiveness
of a windbreak. In arid and semi-arid regions where rainfall is insufi cient to establish
vegetative cover, mulching may be used to conserve moisture, prevent surface crusting,
reduce runoff and erosion, and help establish vegetation. Storage piles can also be sited in
order to take advantage of existing landscape features and vegetation, which can act as a
windbreak.
Site rehabilitation including providing for adequate landforms and revegetation of
disturbed areas and mine waste placement areas provides the only feasible long-term
preventive erosion measures after mining operations cease. Mine waste placement areas
are designed to last for centuries, and relying on nature to prevent both water and wind
erosion is the only feasible option.

As a rule of thumb, surfaces
of completed earthworks
(including landscaping) should
be re-vegetated (i.e. seeded and
mulched) within one or two
weeks after active operations
have ceased.