Environmental Engineering Reference
In-Depth Information
5.6 Concluding Remarks
5.6.1 Mining Activities
Harvesting of nonrenewable natural resources brings with it at least three major areas of
geoenvironmental impacts: (1) depletion of the nonrenewable resource, (2) mining excava-
tions on the surface and underground, and (3) discharges from processes associated with
extraction of the natural resource. The biological components of the terrestrial ecosystem
are not covered in the discussions in this topic. We have focused speciically on the land-use
aspect of the geoenvironment in mining operations as an upstream activity. The use of the
raw materials obtained from such mining operations by downstream industries is covered
in Chapter 7. From the viewpoint of geoenvironment sustainability, we accept that deple-
tion of nonrenewable or depleting resources will not qualify for inclusion in any category of
sustainable resources. This means that if one requires land use to be sustainable, one must
deal with the physical landscape problems raised by above- and below-ground mining pro-
cesses, together with operations and discharges from extraction and beneiciation processes.
Underground mining excavations pose problems in two categories: (1) the physical
aspect of excavations as empty chambers, tunnels, etc., together with the heaping of debris
and other spoils as heaps and tips and (2) the chemical problem represented by acid gen-
eration and the resultant AMD problem because of the interaction of the exposed sulide
minerals in the mined-out areas to oxygen and water. If sustainable land use requires one
to return the land to its
ab initio
condition, this would mean illing the empty mined-out
chambers and excavations. This would, or should, avoid or minimize the problem of acid
generation. Since practical and economic considerations have so far militated against this
course of action, attention has been directed toward mitigating AMD and ARD problems.
5.6.2 Contaminated Water Management
The problem of water usage and “what happens to the used water,” which most often
is contaminated with products issuing from extraction/beneiciation and from usage in
underground in situ extraction of hydrocarbons (SAGD, CSS, and fracking), is perhaps
one of the most critical problems that requires considerable management to avoid and/
or minimize chemical stressor impacts on the geoenvironment. Two particular issues
or concerns need attention: (1) generation of acid leachates giving rise to the commonly
identiied problem of AMD and (2) contamination of shallow and deep-seated aquifers
from “used waters” associated with underground in situ hydrocarbon extraction practices.
Cleaning up contaminated aquifers is a task that is almost impossible, not without some
considerable expenditure and time. To avoid contamination of groundwater and aquifers,
it is essential to implement monitoring of water movement in the subsurface through the
use of monitoring wells and through systematic evaluation of the hydrogeological set-
tings and continuous hydrochemical analyses of abstracted samples from the monitoring
wells. The use of appropriate and valid analytical transport and fate models that address
site- and project-speciic in situ hydrocarbon extraction process, whether it be the steam-
assisted processes or the fracking process, would add considerable value to the monitoring
schemes required to ensure that hydraulic stressors carrying contaminants are not deliv-
ered to receiving waters—above ground and groundwater and aquifers.
Measures undertaken by industry to better protect against acid generation in present
mining and extraction operations, and in underground in situ hydrocarbon extraction
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