Explanation:

 • It involves digging of very small tunnels, usually only 3-4 feet high, which workers enter and extract coal.
• The rat-hole mining is broadly of two types. In side-cutting procedure, narrow tunnels are dug on the hill slopes and workers go inside until they find the coal seam. The coal seam in hills of Meghalaya is very thin, less than 2 m in most cases. In the other type of rat-hole mining, called box-cutting, a rectangular opening is made, varying from 10 to 100 sq m, and through that is dug a vertical pit, 100 to 400 feet deep. Once the coal seam is found, rat-hole-sized tunnels are dug horizontally through which workers can extract the coal.

• The National Green Tribunal (NGT) banned rat hole mining in 2014, and retained the ban in 2015, on grounds of it being unscientific and unsafe for workers.
• The rat-hole mining in Meghalaya had caused the water in the Kopili river (it flows through Meghalaya and Assam) to turn acidic.