Coal Mine Water Drainage: The Current Status and Challenges

Abstract

Any form of mining is a potential threat to the environment. The extent of environmental degradation depends on the status of mine (working/abandoned), type of deposit, mining and processing methods and the geo-atmospheric conditions. Coal mining has huge impacts to local water resources, both surface and ground water. Surface waters are being contaminated through the discharge of mine water, which is also called mine drainage. Ground water is being contaminated due to pilfer of the aquifers. Coal mine drainage is found heavily acidic throughout the world. High acidic water also poses to contaminate with toxic heavy metal ions. Heavy metal pollution comprises the trace occurrences of elements, namely, arsenic, lead, cadmium, cobalt, copper and zinc, coming from the host rock on its exposure to mine drainage water in acidic environment. As the mine water flows over the host rock, metals are leached into the water and mix with the surface waterbodies. These chemicals can be highly toxic to humans and wildlife. Though the heavy metals can dissolve in mine drainage even in non-acidic pH conditions also, but leaching is increased manifold in the acidic environment. From underground coal mines, million liters of mine water is daily disposed to the natural water sources, which are commonly used by the local inhabitants. Most of the Indian coal mines are not generating acidic drainage due to dearth of pyrites in the seams. Thus, it is a common belief that Indian coal mine drainage does not need treatment for heavy metals and is directly discharged into the surface streams. This present study shows that despite the non-acidic mine drainage, Indian coal mine water comprises high heavy metal contaminants and demands immediate attention. It is also revealed that Indian coal mine drainage shows neutral/slightly alkaline water despite having significant iron content.