There are several ways in which gold mining can affect water quality.
The following information is taken from the Safe Drinking Water Foundation online article, entitled "Mining and Water Pollution." Local photos are displayed, pertaining to Buckhorn Mountain and the associated facilities.
While there have been improvements to mining practices in recent years, significant environmental risks remain. Negative impacts can vary from the sedimentation caused by poorly built roads during exploration through to the sediment, and disturbance of water during
mine construction. Water pollution from mine waste rock and tailings may need to be managed for decades, if not centuries, after closure. These impacts depend on a variety of factors, such as the sensitivity of local terrain, the composition of minerals being mined, the
type of technology employed, the skill, knowledge and environmental commitment of the company, and finally, our ability to monitor and enforce compliance with environmental regulations. One of the problems is that mining has become more mechanized and therefore
able to handle more rock and ore material than ever before. Therefore, mine waste has multiplied enormously. As mine technologies are developed to make it more profitable to mine
low grade ore, even more waste will be generated in the future.
Waste from the Mining Process
Ore is mineralized rock containing a valued metal such as gold... The ore is crushed into finely ground tailings for processing with various chemicals and separating processes to extract the final product.
Types of Water Pollution from Mining
There are four main types of mining impacts on water quality.
1. Acid Mine Drainage
Acid Rock Drainage (ARD) is a natural process whereby sulphuric acid is produced when sulphides in rocks are exposed to air and water. Acid Mine Drainage (AMD) is essentially the same process, greatly magnified. When large quantities of rock containing sulphide minerals
are excavated from an open pit or opened up in an underground mine, it reacts with water and oxygen to create sulphuric acid. When the water reaches a certain level of acidity, a naturally occurring type of bacteria called Thiobacillus ferroxidans may kick in, accelerating the oxidation and acidification processes, leaching even more trace metals from the wastes. The acid will leach from the rock as long as its source rock is exposed to air and water and until the sulphides are leached out – a process that can last hundreds, even thousands of years. Acid is carried off the minesite by rainwater or surface drainage and deposited into nearby streams, rivers, lakes and groundwater. AMD severely degrades water quality, and can kill aquatic life and make water virtually unusable.
2. Heavy Metal Contamination & Leaching
Heavy metal pollution is caused when such metals as arsenic, cobalt, copper, cadmium, lead, silver and zinc contained in excavated rock or exposed in an underground mine come in contact with water. Metals are leached out and carried downstream as water washes over the rock surface. Although metals can become mobile in neutral pH conditions, leaching is particularly accelerated in the low pH conditions such as are created by Acid Mine Drainage.
3. Processing Chemicals Pollution
This kind of pollution occurs when chemical agents (such as cyanide or sulphuric acid used by mining companies to separate the target mineral from the ore) spill, leak, or leach from the mine site into nearby water bodies. These chemicals can be highly toxic to humans and wildlife.
4. Erosion and Sedimentation
Mineral development disturbs soil and rock in the course of constructing and maintaining roads, open pits, and waste impoundments. In the absence of adequate prevention and control strategies, erosion of the exposed earth may carry substantial amounts of sediment into streams, rivers and lakes. Excessive sediment can clog riverbeds and smother watershed vegetation, wildlife habitat and aquatic organisms.
Mining can deplete surface and groundwater supplies. Groundwater withdrawals may damage or destroy streamside habitat many miles from the actual mine site.
[end quote from the Mining and Water Pollution article]
Water Quantity Issues at the Existing Mine: Spring 2010 was very rainy, and at the Buckhorn Mine, 7.5 million gallons of water were stored in sumps in mine shafts. The mining company is required to treat water from the mine shafts and from the dewatering wells. Since last spring, the company has taken measures to increase the capacity of their water treatment system. Before these measures were completed, the company trucked waste water (25-30 gpm or over a million gallons per month) to the tailings pond. There was no environmental review, mitigation or permitting for this out of basin transfer of water.
Water Quantity Issues in the Proposed Buckhorn Exploration (2010-2014): The proposed Plan of Operations calls for 120,000 gallons of water to be used per day. This roughly equates to the average U.S. annual household water usage being used daily for the exploration. This would involve a generator-powered well, large steel water tanks or towers, and water to be transported 30 trips per day in 4,000 gallon trucks, 5.6 miles to the mine site, to fill a 300,000 gallon tank and/or 6,000 to 12,000 gallon portable tanks. From the tanks, water would be trucked or piped depending on the location. These figures do not address the quantity of water that would be required should the exploration lead to new mining activity.
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