Open-pit mining
After mining finishes, the mine area may undergo land rehabilitation. Waste dumps are contoured to flatten them out, to further stabilise them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access of rain and oxygen from the air, which can oxidise the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals. There are no long term studies on the success of these covers due to the relatively short time in which large scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become "acid neutral" and stop leaching to the environment. The dumps are usually fenced off to prevent livestock denuding them of vegetation. The open pit is then surrounded with a fence, to prevent access, and it generally eventually fills up with ground water. In arid areas it may not fill due to deep groundwater levels. Instead of returning the land to its former natural state, it may also be reused, converting it into recreational parks or even residential/mixed communities.
Aldridge
In the 1800s, Aldridge became an industrial town with coal mines and lime kilns. The coal and clay in the area prompted many to set up collieries and brickworks. Aldridge clay is especially useful in the manufacture of blue bricks. The 1881 census shows that the mines and brickworks were major employers. Because the coal and clay beneath the eastern side of Aldridge (towards Stonnall) is located much deeper under the surface, extraction of this coal and clay would not have been economically viable. As a result, farms continued to dominate the eastern part, though a sand quarry was set up and still remains on Birch Lane.