Spoil tip

A spoil tip (also called a boney pile, gob pile, bing or pit heap) is a pile built of accumulated spoil - the overburden removed during coal and ore mining. These waste materials are generally composed of shale, as well as smaller quantities of carboniferous sandstone and various other residues. Spoil tips are not formed of slag, but in some areas they are referred to as slag heaps.

Spoil is distinct from tailings, which is the processed material that remains after the valuable components have been extracted from ore.

Physical description

Spoil tips may be conical in shape, and can appear as conspicuous features of the landscape, or they may be much flatter and eroded, especially if vegetation has established itself. The highest in Europe is in Loos-en-Gohelle in the former mining area of Pas-de-Calais. It comprises a range of five cones, of which two reach 180 metres (590 ft), surpassing the highest peak in Flanders, Mont Cassel.

Environmental effects

Spoil tips sometimes grew 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.

Subterranean combustion

As some spoil tips resulting from industries such as coal or oil shale production can contain a relatively high proportion of hydrocarbons, they can commence spontaneous subterranean combustion, which can be followed by surface fires.

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 weak environmental and public health impact of these fires leads generally to waiting for their natural extinction, which can take a number of decades.

Landslip

With spoil tips there is a danger of landslip. An example was the Aberfan disaster in Wales 1966, in which a total 144 people were killed, 116 of whom were school children, mostly between the ages of 7 and 10. Five teachers also died in the accident.

Reuse

The question of re-utilisation of spoil tips is sometimes raised.

At Nœux-les-Mines, an artificial ski slope has been provided on an old spoil tip, the building of which has provided it with a novel use.
Because they are inappropriate for building purposes, old spoil tips can be partially revegetated and provide valuable green spaces.
Some spoil tips contain residual coal and evolving techniques allow renewed exploitation of this asset.
There has also been research into various recycling techniques, which result in spoil being removed from the site and potentially used for other commercial or construction purposes.

The oldest coal-based spoil tips may still contain enough coal to begin spontaneous slow combustion. This results in a form of vitrification of the shale, which then acquires sufficient mechanical strength to be of use in road construction. Some can therefore have a new life in being thus exploited; for example, the flattened pile of residue from the 11/19 site of Loos-en-Gohelle. Conversely, others are painstakingly preserved on account of their ecological wealth. With the passage of time, they become colonised with a variety of flora and fauna, sometimes foreign to the region. This diversity follows the mining exploitation. For example, because the miners threw their apple or pear cores into the wagons, the spoil tips became colonised with fruit trees. One can even observe the proliferation of buckler-leaved sorrel (French sorrel - Rumex scutatus), the seeds of which have been carried within the cracks in the pine timber used in the mines. Furthermore, on account of its dark colour, the South face of the spoil tip is significantly warmer than its surroundings, which contributes to the diverse ecology of the area. In this way, the spoil tip of Pinchonvalles, at Avion, hosts 200 different varieties of higher plants. Some thirty species of birds nest there.

Some cultivate vines, as in the case of spoil tip No7 of the coal-mining region of Mariemont-Bascoup near Chapelle-lez-Herlaimont (province of Hainaut) which produces some 3,000 litres of wine each year.

Some spoil tips provide for various sporting activities. The slopes of the spoil tips of 11/19 at Loos-en-Gohelle, or again, at Nœux-les-Mines, are used for winter sports, for example ski and luge, since the provision of a piste on the flank of the heap. In Belgium, a long distance footpath along the spoil tips (French: terrils) (GR-412, Sentier des terrils) was opened in 2005. It leads from Bernissart in western Hainaut to Blegny in the province of Liège.

In the United States, mining companies have not been allowed to leave behind abandoned piles since the Surface Mining Control and Reclamation Act was passed in 1977.

External links

Spoil heap 11/19 in Loos-en-Gohelle Template:Fr icon
chaine.des.terrils.free.fr/ Template:Fr icon
Turning coal waste into light, 8 October 2004
Photo of a typical coal breaker with culm bank
Breaker Boys and Bony Pickers, 28 November 2006
Management of Disused Tips UK Department of Energy
Waste Rock and ARD