Understanding rat-hole mining

Subject: Environment

Section: Pollution

Context:

Two scientific methods of mining — vertical drilling and auger or horizontal drilling — were employed to rescue 41 workers on November 28 after 17 days of being trapped in the partially collapsed Silkyara tunnel in Uttarakhand. The last leg of the rescue involved rat-hole mining once used extensively in Meghalaya.

Coal in Meghalaya:

The State has an estimated reserve of 576.48 million tonnes of low-ash, high-sulphur coal belonging to the Eocene age (33-56 million years ago).
Unlike in Chhattisgarh and Jharkhand, coal seams in Meghalaya are very thin. This makes rat-hole mining more economically viable than opencast mining.

Auger mining:

Auger mining is a relatively low-cost method of coal mining and is practical in areas where the overburden (material covering the coal seam) is too thick to be removed economically or where the coal seam is too thin for underground mining.
Auger mining uses large-diameter drills mounted on mobile equipment to bore into a coal seam. Holes are horizontally drilled at regular intervals to depths of as much as 1,000 feet. As the cutting head of the auger bites into the coalface, the cut coal is carried out by the screw portion of the bit. Once the hole is mined to its required depth, the auger machine is moved a few feet and another hole is drilled.

Rat hole mining:

Rat-hole mining involves digging tunnels 3-4 feet deep, barely allowing workers to crawl in and out. They have to squat while extracting coal with pickaxes.
Two types:
- The side-cutting type of mining is usually done on hill slopes by following a coal seam — dark brown or black-banded coal deposited within layers of rock— visible from the outside.
- The second type called box-cutting entails digging a circular or squarish pit at least 5 sq. metre in width up to a depth of 400 feet.
Miners who drop down in makeshift cranes or using rope-and-bamboo ladders dig horizontally after finding the coal seam. The tunnels are dug in every direction from the edge of the pit, resembling the tentacles of an octopus.
It was banned by the National Green Tribunal (NGT) in April 2014.

The negative impact of Rat-hole mining:

Asphyxiation because of poor ventilation, collapse of mines due to lack of structural support, flooding, land degradation, deforestation, and water with high concentrations of sulphates, iron, and toxic heavy metals, low dissolved oxygen, and high biochemical oxygen demand.
At least two rivers, Lukha and Myntdu, became too acidic to sustain aquatic life.

Why is such mining banned?

The Coal Mines Nationalisation Act of 1973 is not applicable in Meghalaya, due to being a sixth schedule state. The landowners are thus also the owners of the minerals beneath.
There is a widespread issue of human trafficking and child labour in these mines and at least 17 miners were drowned in an illegal mine in the East Jaintia Hills district’s Ksan in December 2018 after water gushed in from a river.