Underground
mining is the extraction of minerals of economic value that lie below the
Earth’s surface, their conveyance to the surface, and processing (including ore
handling, crushing, milling, screening-separation, washing, concentration, and
smelting). Shafts and tunnels linked to the surface provide access to the
ore-bearing vein, layer, or host rock. Every step of underground or hardrock
mining, from exploration, development on mining infrastructure, through
post-closure, has the potential to generate adverse environmental and social
consequences. In addition to the obvious disturbance of the land surface
through construction of roads and a great number of mining-milling operations,
mining may affect to varying degrees air, aquatic organisms, ground and surface
waters, socioeconomic patterns, soils, terrestrial vegetation, and wildlife
resources. Certain of the key adverse effects are outlined below and discussed
briefly.[1]
Air Quality issues generated by mining-milling-smeltering
operations include emissions of particulates, fugitive dust, odors, and
sulfuric acid that can produce extensive regional air pollution through
sulfuric deposition and acidification of streams and lakes that in turn can
cause adverse changes in aquatic biotic composition and chemical processes. Those
adverse atmospheric effects can be felt many hundreds of miles from the mining
source in cities and even other countries. The above issues associated with the
atmosphere around or in the vicinity of surface operations can also adversely
affect air within underground mines and is of great consequence, especially to
those inside the mine. Heat, dust, oxygen deficiency, carbon dioxide, carbon
monoxide, hydrogen sulfide, nitrogen oxide, methane and other natural gases,
and hydrocarbon aerosols among others can result in poisoning, explosions,
fatigue, disorientation, asphyxia, and death.
Aquatic Biota can be adversely affected by mining in three ways.
First, cyanide and metals that are toxic to aquatic life even at low
concentrations can seriously impair the functioning of natural and cultural
aquatic ecosystems. Second, acid drainage and leaching of materials with high
concentrations of sulfates and chlorides can adversely affect pH requirements
and result in precipitations that can coat stream beds with iron-rich and heavy
metal-rich cements, impairing habitat for fish and macro-invertebrates by
reducing the spaces between gravels with very fine-grained sediment,
threatening egg survival through oxygen deprivation; those adverse acid drainage effects have been known to persist in some mines for centuries. Third, placer mining in
active streams can disturb or completely destroy stream bed sediments that
provide habitat for macro-invertebrates and spawning habitat for salmonids.
Landscape/Ecosystem Alterations can be caused by exploration or access roads,
construction of mining-smelting infrastructure — such as cranes, hoists,
conveyor systems, buildings, electrical substations and distribution lines,
power generating equipment and facilities, workshops, showers and
decontamination facilities, testing labs, wastewater treatment facilities,
offices, parking-vehicle storage areas, material storage, and smelters, etc. — the
use of mechanized equipment such as off-road vehicles, drill rigs, or seismic
exploration vehicles and construction-operation of mining activities in
previously remote, roadless, mountainous regions, high latitudes, or wetlands
where human activity had resulted in little alteration of relatively pristine
ecosystems.
Natural Riparian Vegetation has been damaged and decreased and even totally
destroyed when valleys have been used as sites for placing waste rock in areas
where mountaintop removal is practiced. Obviously, if a valley is filled with
several hundred feet of waste rock, the vegetation, habitat, and the valley
itself will be drastically altered and most likely can never be restored. Other
mining activities that adversely affect riparian vegetation include the
placement of leach pads, tailings impoundments, and even major mining-milling
facilities. In some areas, particularly but not exclusively in the American
Southwest, mining activities can potentially consume much if not all the
locally available water through extensive dewatering and groundwater
withdrawal, which may affect surface flow and disrupt shallow and even regional
aquifers and spring flows with the effects of stressing riparian vegetation,
causing either reduced vigor or mortality. Contaminated substrates can be
created when metal-contaminated water and sediments reach wetlands or settle
along streams in wetland or riparian zones, adversely affecting plants that
take up metals and store them in foliage and stems. In addition, contaminated
soils and sediments from mine sites can negatively affect stream bank, stream
bed, and floodplain sediments, as well as down-gradient wetlands and riparian
systems located at some distance from mining activities.[2]
Noise and Vibration from heavy equipment, blasting, and milling
operations at mine facilities adjacent to rural residential settlement or
larger communities may cause people to abandoned their homes and move away or
change their behavior in an effort to avoid adverse effects. Research conducted
over the past thirty years, particularly into noise from aircraft operations on
human receptors, has demonstrated that constant noise and vibration can cause
serious physical and emotional impairment in human as well as animal
populations.
Surface and Sub-Surface Soils can be altered, indurated, contaminated, or
otherwise adversely affected by road building or mining construction to certain
depths below the surface such that short-term and even mid-term recovery
following reclamation is problematic. The fairly intense disturbance of soil
surfaces by mining activities may make soils susceptible to water and wind
erosion, thus contributing to sediment loading in local or regional stream
systems that reduce water quality and aquatic habitat. Chemical particulates
and metals from smelter emissions and blowing tailings can settle on soil
surfaces near or some distance from mineral processing facilities although
typically contamination of soils decreases with distance from the contaminant
source. Real World Example: The
Omaha Lead site in the City of Omaha, Nebraska, includes surface soils present
at residential lots, child care facilities, schools, and other residential-type
properties that have been contaminated as a result of air emissions from the
ASARCO (originally American Smelting and Refining Company, now a wholly owned
subsidiary of Grupo Mexico
[1] Much of the information in this definition was
adapted from: Committee on Hardrock Mining on Federal Lands, Committee on Earth
Resources, Board on Earth Sciences and Resources, Commission on Geosciences,
Environment, and Resources; National Research Council, Hardrock Mining on Federal Lands: National Academy Press,
Washington, DC: http://books.nap.edu/html/hardrock_fed_lands/index.html
as well as from the German Federal Ministry for Economic Cooperation and
Development materials (Environmental Handbook — Documentation on Monitoring and
Evaluating Environmental Impacts) on underground mining and its environmental
effects posted on the Centre for
Ecological Sciences, Indian Institute of Sciences web site: http://ces.iisc.ernet.in/energy/HC270799/HDL/ENV/enven/vol214.htm#37.
percent20Underground percent20mining
[2] For a
book full of ugly examples of how mining can kill a mountain ecosystem and the
surrounding valleys, see: Erik Reece, Lost
Mountain: A Year in the Vanishing Wilderness. New York
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