Water is essential for human existence, ecosystem health, wildlife, and various kinds of economic activity. It is also a limited resource. Wise use, management, and conservation are critical to balancing and meeting these needs.
Water is used throughout the mining process; without an economical water supply, the growth of the mining industry in Nevada over the past three decades would not have been possible. The acquisition of rights and permits to appropriate water for these uses are critical steps in large-scale mine development.
Some individual mine sites may have increased concentrations of specific metals and salts in water used in – or runoff from – mine sites. Acid mine drainage (AMD) is a phenomenon that can occur when rock containing sulfides is exposed to air and water. The water can become acidic and often carries elevated levels of toxic metals. AMD occurs most frequently in association with metals mines and can affect water quality.
Pit lakes, another water-quality concern during and after
mine closure, are created when mining is completed in a pit
and dewatering pumps are turned off, allowing groundwater
to flow back into the pit. Similar concerns about the acidity
and concentration of heavy metals in these water bodies arise
in association with metals mines.
Changes in water quality and quantity can affect not only human health but also wildlife habitat and ecosystem health. Environmental impact assessment processes often intensively focus on biodiversity issues in Nevada, and as a consequence, operating plans require significant dedication to design of mitigation and management efforts.
Mining companies use a variety of techniques to reduce, conserve,
and recycle water from mining processes—and to reuse
it to meet other needs, such as irrigation or restoring it
to the groundwater system. Some techniques include:
- Using saline water that is unsuitable for agriculture or domestic use for processing ore
- Using groundwater pumped from mining excavations for processing
- Re-use and recycling of water for ore processing to reduce the total water required
- Returning water to surface waters or to groundwater systems via infiltration ponds or reinjection into aquifers after treatment to ensure it meets water-quality standards
Companies also implement protective management measures and technologies to avoid or minimize impacts on water quality and meet regulatory standards. These include:
- Testing to determine the potential for acid
mine drainage from waste dumps, leach piles, and tailings
- Design of management strategies and technical
solutions to prevent acid mine drainage and the acidification
of pit lakes. Detailed management plans aimed at mitigating
and minimizing exposure to air and water of sulfide minerals
in waste rock and processed ore are created by mining companies
and reviewed and approved by regulatory agencies. Similar
plans are created for pit lakes
- Use of water treatment plants to treat dewatering
water prior to discharge either to surface or groundwater
At a Glance: Water Regulation
In Nevada companies pursuing new mining projects must apply
for water use permits from the Nevada Division of Environmental
Protection Bureau of Mining Regulation and Reclamation as
a part of the project’s Plan of Operations.
The Division of Water Resources (a sister agency to the Division to Environmental Protection, under the Department of Conservation and Natural Resources) administers all surface and groundwater in the state. Companies can acquire water only through permits, which requires, among other things, evaluation of the impact to proposed surface and groundwater withdrawals before permits are issued.
Discharge of water from mining operations is regulated by
the State of Nevada and by federal statutes, such as the Clean
Water Act and Safe Drinking Water Act.
Mining operations are required to obtain several permits,
which set guidelines for controlling water pollution through
establishment of discharge standards. These permits include
National Pollution Discharge Elimination System permits (which
regulate point sources for pollution) and Stormwater Pollution
Prevention plans in case of overflow. These permits set limits
on the amounts of particular substances that can be discharged
in water, to protect public and environmental health.