In essence, environmental impacts from mining are those that directly and indirectly affect ecological and human health. The type of mining and operations results in different environmental and human health impacts but they can generally be grouped into major categories. Those categories are:
Metal contamination of ground and water
In either open-pit or underground mine sites, both mining methods pose the risk of water contamination through contact with surface water or groundwater. Contamination of groundwater may cut off or limit the supply to nearby areas. For surface water, dissolved metals like sulfates, radio-nuclides, and nitrates may travel through streams, or through erosion be carried to local groundwater. In reference to mining, the chemicals used in processing the ores are a source of contamination. This affects the quality of water sources in nearby communities and will affect aquatic life.
In Utah, from 1910 to 1972 the International Smelting and Refining Company (IS&R) had lead, copper, and zinc smelting and refining activities in Tooele County that caused contamination of the smelter property and adjacent lands of neighboring towns including the Lincoln Township.
Site investigations found heavy metal contamination in soils, tailings, and slag. Up to 18 inches of contaminated soil has been removed and excavated from the public, commercial, and residential affected areas. Capping was also implemented on areas where the soil was not removed, fences were installed in restricted areas that cannot be remediated due to access limitations and physical hazards, and contaminated soil up to 24 inches thick is removed and backfilled with clean ones to revegetate the area. The site remediation process took 11 years from 2000 to 2011, the site is now known as the Pine Canyon Conservation Area.
Structural instability in mining is when the soil aggregates are unable to resist degradation caused by changes to the surrounding soils. In mining, instability is most often seen around tailings disposal systems – especially with older mine sites. When the stability of the tailings fails it could result in the release of contaminants into the environment and waterways.
In 1972 at Buffalo Creek, West Virginia, Pittston Coal’s slurry impoundment collapsed due to heavy rain releasing 500,000 m3 of tailings that traveled 27 km downstream, demolishing 500 homes, 125 casualties, and $65 million in property damage. This disaster has a significant impact in the country and it has lead to senate hearings that passed Public Law 92-367 and the creation of the National Dam Safety Program that focuses on creating dam safety programs to reduce the risk to human life, property, and the environment from dam related hazards.
Using the lessons from the past, tailing systems today are being designed to take into consideration the physical characteristics of the waste material as well as conditions on-site. Nowadays, most tailing disposal systems have special liners and are equipped with earthquake-ready measures.
For our purposes, slopes in mine sites are either cut or manufactured. Cut slopes are slopes created from the removal of ore or overburden rocks from the surface of an undisturbed landscape. Manufactured slopes are the slopes created in piling and dumping waste rock, overburden, and tailings. Slope failure tends to spread these wastes, releasing toxic or reactive materials to its surroundings.
In 2013, the Bingham Canyon copper minefield in Utah operated by Rio Tinto-Kennecott had two consecutive avalanches that displaced a total of 65 to 70 million m3 of dirt and rocks, which is considered as one of the largest non-volcanic landslides in Northern America. The Manefay Landslide has caused damage to the mine site and has resulted in significant immense economic costs. Through the installed interferometric radar system, movement of up to 2 inches a day were detected and warnings are sent out to the workers and nearby communities that a landslide is imminent. Mining operations were shut down a day before the landslide and there were no injuries or casualties. Though anticipated, the extent of damage was unexpected, destroying large mining shovels, thirteen 320 ton trucks, roads, buildings, and other equipment and supplies.
There are many methods in measuring safety parameters from the combination of the earth to satellite-based technologies or traditional to remote sensing techniques to manage or predict slope instabilities. Proper design analysis through numerical modeling, as well as analytical, and empirical techniques to identify zones of weakness and probability of slope failures provides information to which site managers can strategize risk management plans from.
Subsidence is the lateral ground movement resulting from the collapse of an overlying layer into an underground mine cavity. Subsidence occurs in underground mine sites when pockets of unfilled rooms or collapsing supports and pillars are triggered by surface movements. Sinkholes and land troughs are manifestations of subsidence and are highly destructive to the community that is unaware of the extent of the excavation activity of old, inactive or abandoned underground mines.
In Pennsylvania, where coal and clay mining began for over 200 years, the state is still dealing with mine subsidence threats as more than 1 million residential homes are situated above lands that are historically mined using the room and pillar method. Mine subsidence is devastating and destructive not only to the structures above it but it also affects the overlying aquifer’s drainage patterns, misdirection of streams, and disruption on wells and irrigation systems.
Even though the timing and extent of subsidence damage are inevitable, there are some remediation techniques and prevention measures that can be implemented. For room and pillar mines with insufficient pillar support, backfilling with rock, mine wastes, or cement grout can be applied until mined out voids are filled. Roof supports and the construction of grout columns can be implemented to prevent subsidence as well.
Acid mine drainage (AMD) is the outflow of acidic water that is generated in the oxidation of pyrite or iron ores rich in sulfur. It is also commonly referred to as Acid Rock Drainage (ARD). Acid is produced when mined materials such as excavated host rocks with metal sulfide minerals are exposed to air and water. Acid drainage sites may contain dissolved metals like lead, copper, silver, iron, and zinc. High concentrations of these dissolved metals affect aquatic life and the quality of water in streams.
Iron Mountain Mine
The US mining industry considers acid drainage as its largest environmental problem. It may occur rapidly or it may take years to manifest and exhaust its full damage extent. The Iron Mountain Mine or Richmond Mine’s 4,400-acre land has been mined for many resources such as iron, copper, gold, silver, and zinc for more than 100 years until mining operations halted in 1963. Even after mining in the Richmond mine was stopped, the mining activities have left the mountain fractured. Its minerals were exposed to rain and air that leached heavy metals like cadmium and copper to seep out of the mine site and reach the Spring Creek Reservoir. The acidic water with low pH levels and high metal concentrations have resulted in fish kills, including the migrating salmons in the 1940s, the elimination of other aquatic life and contamination of potable water of neighboring communities in Spring Creek, Boulder Creek, and Slickrock Creek as well.
The occurrence and extent of acid mine drainage vary from site to site depending on the generation factor or the capability of a material to react and produce acid. Physical factors such as the waste structure, particle size, permeability, and the local hydrology are contributors that will affect the site’s potential to produce AMD.
Cyanide is used in the beneficiation process during gold and silver recovery. In low doses, cyanide is acutely toxic to humans and according to the International Cyanide Management code, commercial gold operations only typically use 100 to 500 parts per million (.01 to 0.05%) of cyanide. Fish kills happen when the cyanide is spilled due to the tailings dam design failure or poor waste management practices.
The Summitville Mine in Rio Grande County, Colorado has been mined from the 1870s up until 1992 when a cease and desist order from the state government was issued due to the alarming contamination levels in the area affecting nearby creeks and community. Concerns on the run-off of excess water from the heap leach pad- an estimate of 320 m3 had leaked from the damaged liner. Another major cyanide release was caused by a pump failure that resulted in a fish kill downstream along the Alamosa River.
Cyanide is a toxic material that can be ingested or inhaled and constant exposure could be lethal. Nowadays, the use of cyanide has declined as less harmful alternatives are already available in the market. The chemical was mostly used during the 70s and 80s – but began to decrease in the 90s due to political pressure and environmental impacts.
Gaseous and particulate emissions are both released in heat treatment, beneficiation, mining, and mineral processing. Particulate Matter (PM) released from mining have sizes ranging from 2.5 micrometers (PM2.5) to 10 micrometers (PM10) of aerodynamic diameter.
PM10 coarse particles can form into fugitive clouds of dust that are generated from mining activities like blasting, loading, hauling, dumping waste rocks, as well as crushing activities. PM2.5 covers all suspended particulate matters that are less than 2.5 micrometers in diameter and are mostly released from other combustion processes. Flue dust comes from sinter, roaster, and refinery stacks. The spread of fine particulate matter is dependent on the height of the stack. While the release is in low concentration, the deposition of the metals over time, decades to centuries, becomes substantial to contaminate the air and soil.
Air emissions can cause an adverse effect on the respiratory health of the people living near mine sites. Studies show that the exposure of the locals to both fine and coarse particles have a correlation to increased hospital respiratory disease admissions, restricted activity days, and respiratory symptom cases attributable to the direct impact of the mining .
State agencies such as the Environmental Protection Agency (EPA) have regulatory actions and mandates that set specific targets for operators to follow in order to legally enforce commitment to the reduction of air emission risks. The Clean Air Act has also established standards that operators must meet and comply to regulate the release of air pollutants for the protection of the community and the safety of the mineworkers.