Logging and Mining
Water is used in mining to extract solids, such as coal, gravel, and sand, liquids, such as crude petroleum, and gases, such as natural gas. Water is also used to cool equipment, generate power, and suppress dust. In the process of mining, many substances that would otherwise be buried underground are brought to the surface and can become water quality concerns after being exposed to the atmosphere and water. Logging can also have deleterious effects on water quality.
WATER QUALITY CONCERNS
If air, water, and sulfur-containing rocks mix, chemical reactions can lead to the formation of sulfuric acid and iron hydroxide. This acid runoff dissolves certain heavy metals (e.g., copper, lead, and mercury) which contaminate waterways. Acid mine drainage can also affect the pH of water. Water with an extremely high or low pH is deadly. Water with relatively low pH (acidic) may reduce the hatching success of fish eggs, irritate fish and aquatic insect gills, and damage membranes.
Source: Western Pennsylvania Conservancy
Ore from various minerals must be separated into two parts, the desired valuable and economic part and the non-valuable waste product. Oftentimes, this is accomplished by pulverizing and adding chemicals to the ore to extract the valuable parts. The non-valuable parts are called "tailings" (gangue). These leftover tailings are generally mixed with water to create a slurry and are stored in long term ponds or behind containment dams.
These containment areas can contain high concentrations of heavy metals such as Zinc, Arsenic, Cadmium, Mercury, and other chemicals. These can come from the chemicals used to extract the valuable portion of the ore, or the rock and sediment itself. The concern for water quality arises when there is a breach in impoundments or leakage into surface or ground water.
Many precautions must be taken to prevent water from running over exposed rock and contaminating water bodies near mining operations. These can be things such as diversion of precipitation and runoff, water recycling, and impermeable liners surrounding ore and rock waste piles. Inevitably, some water will have to be treated. Water exiting mining operations is regulated as a point source pollutant. Permits must be issued that specify maximum amounts of each pollutant that can be discharged.
Water treatment can be either passive or active. In passive treatments, water does not have any additional chemicals added to remove pollutants. An example would be installing wetlands or filtration through soils. In active treatments, chemicals are added to speed up and aid the cleaning process. Active treatment is often conducted with lime, limestone, or caustic soda to elevate pH, as most of the runoff from mines is acidic (below 7 pH). When pH is elevated, many dissolved metals will precipitate out of the water where they are more easily collected. Depending on effluent water quality requirements, some companies may use more complex technologies such as reverse osmosis to get water even cleaner.
INACTIVE AND ABANDONED MINES
Runoff and pollution coming from inactive or abandoned mines present unique challenges to protecting water quality. Pollution from these mines is diffused (not concentrated) and is considered a non-point source pollutant. It is estimated that between 17,000 and 20,000 abandoned mines exist in the state of Utah. The most concerning types of abandoned mines are those that mined metals due to the chemically intensive process and large quantities of waste that are produced. Additionally, many of these mines were opened at times when environmental impacts were not well understood. Much of the waste was put directly into streams, as this was the most expedient way to get rid of waste.
The most common pollution problems from abandoned and inactive mines are:
- Acid Mine Drainage that can enter waterways and water supplies
- Heavy Metal contamination
- Alkaline runoff that is high in salts and sediments
- Breaches in dams, impoundments, and ponds
- Sediment erosion that causes an increase in turbidity
Abandoned mines lack any responsible party, and are therefore even more challenging to clean up after. Similarly, water and pollutants do not adhere to man-made borders. Because much of Utah is federal and state lands, much of the responsibility of reclamation falls on federal and state agencies. Old mining sites, if not cleaned up, can potentially be a source of pollution forever.
Forestry is considered a non-point source pollutant, due to its many diffused and indiscernible sources. The primary water quality concern is increased turbidity in streams due to excess sediment. The increase in sediment can be attributed to removal of riparian vegetation, road building, and mechanical preparation of logging sites. The Environmental Protection Agency (EPA) estimates that road building and road use make up 90% of the total sediment from logging operations.