Environmental Engineering Reference
In-Depth Information
d. Assessment of the required 4R technologies—remediation, reclamation, restoration,
and rehabilitation requirements to meet the required land-use schemes or plans.
e. Assessment of quality of rehabilitated lands.
Matching land quality, land suitability, and site functionality with community or regu-
latory land-use plans and requirements for rehabilitated land use that does not necessarily
mean returning the land to initial conditions, for example, reclamation of land for housing
developments.
5.5.2 Acid Mine Drainage Impact Mitigation
As mentioned previously, other than the presence of metal sulide minerals, the two main
elements in the production of acidic leachates are oxygen and water. These two constitute
the sources for the acid (chemical) stressors. The impacts from these stressors are seen in
the contamination of receiving waters and surface land soils. Although it may not be pos-
sible to totally eliminate or obviate these impacts, there are two clear paths where impact
mitigation can be implemented. These are (1) source control and (2) leachate management.
In the case of source control, the mitigating actions undertaken by the stakeholder include
(a) control of quality of discharges by the stakeholder and (b) control of discharge by lim-
iting and channelization of low into treatment stations prior to discharge. These actions
include technology and processes that are physical, chemical, geochemical, and biogeo-
chemical—and various combinations of these. In the case of leachate management, the
steps taken to mitigate impact of the acid leachates are essentially remediation efforts,
i.e., remediation efforts undertaken “once the horse has left the barn.” These efforts have
been called “passive control methods,” which are designed to minimize the deleterious
effects of acid leachates on the environment by treating the leachates in transport through
the geoenvironment. The industries involved in this type of problem, together with the
pertinent governmental agencies have spent (and are still spending) some considerable
effort in combating AMD. There are countless documents reporting on the various studies
and efforts in “curing the problem,” and the reader is advised to consult these for detailed
elaboration of the various research and case studies undertaken (and also presently under-
way). For the discussion that follows, only the basic elements of the mitigating efforts will
be addressed.
The phenomenon of acid generation from heaps with trace amounts of sulide minerals
and from exposed sulide minerals in mined-out caverns, pits, etc., has been discussed in
Section 5.2. The magnitude of the sets of cascading problems attributed to the actions of
acid leachate cannot be overstated. Cleanup of all the affected areas, mining sites, water-
ways, etc., is estimated in the billions of dollars in North America. Not only is the threat
expressed in terms of acid leachates inding their way onto the land environment and into
receiving waters, but also in terms of release of trace metals into the geoenvironment. The
leachates and released metals will negatively affect the functionality of the various ecosys-
tems that comprise the geoenvironment—causing them to be eventually unsustainable. In
terms of sustainable land use, the obvious protection against such stressors (acid leach-
ates) is to remove conditions and circumstances favorable for generation of acid leachates
through source control. This means denying access to oxygen and water. The principle
of “keep it dry” is a good principle to practice at mine sites. This is an easy statement
to make, but is in reality a very dificult and an almost impossible principle to adhere
to. Since water is an essential element in mining-extraction processes, “keeping it dry”
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