The United States is a net exporter of coal. However, some coal is still imported, mostly for power plants on the eastern and southern coasts of the country, where it is cheaper to ship in coal by sea from South America than transport it from mines in the northern and western United States.1
In the third quarter of 2017, the U.S. exported 24.6 million short tons of coal (12.5% of total production)2 to dozens of countries around the world; the largest markets were India (11.7% of all exports), the Netherlands (10.7%), and South Korea (10.6%).2
The U.S. Energy Information Administration (EIA) estimates that, in 2015, around 12% of world marketed (bought and sold) energy consumption came from renewable sources (biomass, geothermal, hydropower, solar, and wind). EIA projections suggest that this will increase to 17% by 2040.
Frac sand is a type of sand with small, uniform particles. It is injected into the rock formation along with the water used to fracture the rock in the process known as hydraulic fracturing ("fracking"). The sand is used to prop open the fractures that are created. Because the particles are uniform, fluids like water, oil, and gas are able to flow through the spaces between the particles.
Water flowing through active or abandoned mine sites can become polluted by the material being mined. By far the most common mine drainage problem is that of acid mine drainage (AMD). Sulfuric acid is produced when water interacts with sulfur-bearing materials in the presence of oxygen and common bacteria.