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.
Llangolman
The springs emerge in boggy land at the base of the gravel banks, where deposits of blue boulder clay, known by the natives as "indiarubber clay", can also be found. Clay pits close to the farmhouses of Llangolman Farm (still visible) and Llyn are evidence that the clay was once extracted on a significant scale. The study by Jehu mentions that the clay pit at Llyn was down to a depth of 15 to 20 feet, and ladders were required to get in and out. His report goes on to state that the clay is bluish in color and very tough (hence the nickname indiarubber clay). The clay covers the valley bottom from Llyn to Llangolman Farm at a level of over 400 ft.