resulting from
strip mining in
Großräschen, Germany , Sweden, in the 1970s Spoil tips sometimes increased to millions of tons, and, having been abandoned, remain as huge piles today. They trap solar heat, making it difficult (although not impossible) for
vegetation to take root; this encourages erosion and creates dangerous, unstable slopes. Existing techniques for regreening spoil tips include the use of
geotextiles to control erosion as the site is resoiled and simple vegetation such as
grass is seeded on the slope. The piles also create
acid rock drainage, which pollutes streams and rivers.
Environmental problems have included
surface runoff of
silt, and leaching of noxious
chemical compounds from spoil banks exposed to
weathering. These cause
contamination of
ground water, and other problems. In the United States, current state and federal
coal mining regulations require that the earth materials from excavations be removed in such a fashion that they can be replaced after the mining operations cease in a process called
mine reclamation, with oversight of mining corporations. This requires adequate reserves of monetary bonds to guarantee a completion of the reclamation process when mining becomes unprofitable or stops. (See for example, the
Surface Mining Control and Reclamation Act of 1977.)
Subterranean combustion is colored red due to
combustion In some spoil tips, the waste resulting from industries such as coal or oil shale production can contain a relatively high proportion of hydrocarbons or coal dust.
Spontaneous subterranean combustion may result, which can be followed by surface fires. In some coal mining districts, such fires were considered normal and no attempt was made to extinguish them. Such fires can follow slow combustion of residual hydrocarbons. Their extinction can require complete encasement, which can prove impossible for technical and financial reasons. Sprinkling is generally ineffective and injecting water under pressure counter-productive, because it carries oxygen, bringing the risk of explosion. The perceived weak environmental and public health effects of these fires leads generally to waiting for their natural extinction, which can take a number of decades.
Landslides The problem of
landslides in spoil tips was first brought to public attention in October 1966 in the
English speaking world when a spoil tip at
Aberfan in
Glamorgan, Wales, gave way, killing 144 people, 116 of them children. The tip was built over a
spring, increasing its instability, and its height exceeded guidelines. Water from heavy rainfall had built up inside the tip, weakening the structure, until it suddenly collapsed onto a school below. The wider issue of stability had been known about prior to the
Aberfan disaster; for example, it was discussed in a paper by Professor
George Knox in 1927, but received little serious consideration by professional engineers and geologists — even to those directly concerned with mining. Also the Aberfan disaster was not the first landslide with casualties: for example, in 1955 two successive landslides killed 73 people in
Sasebo, Nagasaki in Japan.
[ja] In February 2013, a spoil tip landslip caused the temporary closure of the Scunthorpe to Doncaster railway line in England. Landslides are rare in spoil tips after settling and vegetation growth act to stabilise the spoil. However, when heavy rain falls on spoil tips that are undergoing combustion, infiltrated water changes to
steam; increasing pressure that may lead to a landslide. In
Herstal, Belgium, a landslide on the Petite Bacnure spoil tip in April 1999 closed off a street for many years. ==Re-use==