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Hardrock Mining: Environmental
Impacts
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Fugative Dust
Emissions
Definition
A variety of mining
operations emit particles, usually in the form of fugitive dust. Specific
sources include ore crushing, conveyance of crushed ore, loading bins,
blasting, mine and motor vehicle traffic, use of hauling roads, waste rock
piles, windblown tailings, and disturbed areas. In a few cases, dust can
contain arsenic, lead, and other toxic heavy metals.
Potential Impacts
Particulate matter is an environmental
concern because it can contaminate air. It can also deposit dust in
surface water, causing sedimentation and turbidity.
Habitat
Modification
Definition
Habitat is the
environment in which an organism normally lives. There are three basic
habitat types:
acquatic habitats (e.g., lakes, ponds, streams, rivers)
terrestrial habitats (e.g., deserts, grasslands, forests)
wetlands
Concerns
By its very nature, mining can
cause large disturbances to the land. Not only can there be a direct
impact as a result of mining, but the withdrawal and discharge of water,
manipulation of topography, and releases of particulates and chemicals can
all have indirect impacts on various habitats.
Beneficiation
processes can use large quantities of water. Large withdrawals of
groundwater or surface water can affect aquatic habitats and wetlands by
lowering the water table or decreasing recharge.
Surface Water and
Groundwater
Definition
Hydrology relates to
the flow characteristics and patterns of surface water and groundwater,
including springs, wetlands, brooks, streams, rivers, ponds, lakes, and
aquifers.
Potential Impacts
Mining can impact hydrological systems
by it nature. The massive quantities of water necessary for many
beneficiation processes can disrupt surface water and groundwater flows.
The removal of water from mine workings can result in drawdown. Drawdown
can reduce the amount of water available for recharging wetlands and
surface water, thereby affecting any organisms that depend on those
waters.
Water that percolates through waste piles and tailings can
become contaminated with heavy metals. This water can contaminate both
groundwater and surface water. Additionally, the hydraulic head pressure
of tailings ponds can cause hydraulic mounding underneath and adjacent to
the pond, potentially altering the local groundwater flow pattern.
Control and Remediation
One of the most effective
control measures for minimizing surface water and groundwater impacts is
to reduce the amount of water needed during mining operations as much as
possible. Recycling water can dramatically reduce overall water
withdrawals. Tailing impoundments can be operated to recycle water back to
the mill and can be underlain with a liner to prevent the release of
contaminated water.
The effect of pit design, specifically the
depth of the mining operation, on groundwater and surface water should be
considered. Pits can fill with water after mining is completed and this
water can become contaminated with metals.
Other
Concerns
Subsidence
Mining subsidence is the
surface impact of collapsing overlying strata into mined-out voids.
Subsidence may manifest itself in the form of sinkholes or troughs.
Sinkholes are usually associated with the collapse of a portion of a mine.
Sinkholes or depressions interrupt surface water drainage patterns,
affecting ponds, streams, and wetlands. Reducing the withdrawal of
groundwater through specific practices such as recycling mine water can
reduce the potential for subsidence.
The threat and extent of
subsidence is related to the method of mining employed. In many instances,
traditional room and pillar methods leave enough material in place to
avoid subsidence. However, high volume extraction techniques, such as
pillar retreat and longwall mining, result in a strong likelihood of
subsidence. Preventing subsidence involves leaving support mechanisms
(e.g., pillars) in place after completing the mining operation or
backfilling with waste rock.
Aesthetics
Aesthetics
involve the general visual environment, including the overall scenery and
unique topographical characteristics. Since most mining operations result
in large land disturbances, aesthetic impacts can be significant.
Recontouring the land to reduce unnatural anomalies, backfilling holes,
revegetating, and promoting wildlife habitats can all improve the
aesthetics of a mining operations.
The information contained on these pages is a general
statement of policy. It does not establish or affect legal rights or
obligations. It does not establish a binding norm and is not finally
determinative of the issues addressed. Agency decisions in any particular
case will be made by applying the law and regulations to the specific
facts of the case. |
