EGEE 101
Energy and the Environment

Open Cast (Strip) Mining

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 An enormous coal truck with Dr. Mathews standing next to the wheel. He comes up the middle of the wheel.
There are some very large "Tonka toys" around
surface mines. This truck cost @ $1,000,000 -
no wonder they run it about 22 hours of the day,
about 340 days of the year. 
Credit: ES

In some locations, the coal lies deep in the ground, but in others, only a few feet from the surface. If the material above the coal (overburden) can be removed, then there is easy access to the coal. Sometimes the tops of mountains can be removed to expose the coal, other times vast acreage of mines is created. Either way, this technique requires the ability to move vast quantities of rock and coal. Surface mining is an expensive operation, with environmental challenges, and a great deal of expense. It can, however, extract lots of coal with which to provide the engines of industry (and the computer chips, etc.) the energy they require.

The removal of both the coal and the overburden is performed with some of the largest mining vehicles in existence. First, the overburden is drilled into with power drills. The intent is to use explosives to fragment the various rock layers into manageable chunks that can be removed. Then, the holes are filled with an explosive mixture of fuel oil and fertilizer. The fragmented rock is then scooped with very large buckets via draglines. The process then repeats but this time the coal is fragmented with explosives. This is done by truck, or by miles of coal conveyor belts. After collection, the coal is transported to the breaker. There the coal is crushed and a cursory cleaning is performed to remove the large pieces of rock.

 Picture of a surface mine with holes drilled in the side of a hill with an inset image showing one of the holes going down 40 feet. See caption
A field of holes 40 feet deep awaits the explosive mixture and detonation fuses that set off the explosions one after the other separated by a very small fraction of a second to fragment the rock.
Credit:JPM
 Picture of a small dragline
The draglines are very heavy and slow when moving along on the caterpillar tracks but when in motion, moving the bucket is a swift beast of burden, moving tons of coal with ease. This is a small dragline. Realize that the bucket on a dragline can be the size of a house!
Credit: JPM
 Picture of an area which was surface mined.
This image does not capture the impressive scale of surface anthracite mining at this site. The drop is about 200 feet with the water being another 100 feet deep. This operation had shut down to replace the pumps that keep the workings dry otherwise the water would not be as high.
Credit: JPM
A large quarry with many horizons and ledges.
Mountain Top Removal Mining

A special form of surface mining is Mountain Top Removal. This occurs in locations such as West Virginia and eastern Kentucky. This is a highly contentious form of mining that provides jobs and tax benefits to the region, but damages streams and removes mountains. Dam bursts of coal dust retention ponds have also been a problem.

a valley.  The walls of the valley are covered in gravel. The walls of the valley are covered with grass and wild flowers a surface mine.
Click on the images to learn more about what you are seeing.

The scale of these mines can be very impressive, check out a drone view of a surface coal mine.

Aerial drone view of a huge opencast coal mine cut into a rural hilly area
Aerial drone view of a huge opencast coal mine cut into a rural hilly area

Reclamation

Mining reclamation is now required for all active mines, but that was not always the case. There are many sites where the work finished and the miners and the owners just walked (or ran) away. Not only is mining reclamation the norm these days, but it is also required. Mined land is required to be returned to its original contours. A tax on every ton of coal (15 cents for surface coal) helped to fund "Superfund", a large-scale government environmental program for cleaning up the abandoned mine sites. The fund, which started in 1978, is now in the many millions (fines, interest, and late payments are also included). The ash from fluidized beds is currently used in the anthracite region to fill in the open pits from long ago abandoned strip mines. This reclamation and others help to remediate acid mine drainage, prevent landslides, and aids in recovering land for other useful purposes, such as land development to the West of Pittsburgh International Airport.

So after the coal is removed the overburden is moved back, leveled, the topsoil is returned, and vegetation planted.

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Diagram of the Mining and Reclamation Process
Credit: Feng et al. Earth-Science Reviews, Volume 191, April 2019, Pages 12-25