SHILLONG: A study conducted by the Geological Survey of India (GSI) on the causes for seepage of water in the rat-hole coal mines at Ksan in East Jaintia Hills district has ruled out the Lytein river flowing nearby contributing to any “lateral seepage.”
A team of geologists and geophysicists from the GSI North Eastern Region visited the site on January 15 to assess the probable cause of seepage of water in the underground coal mining areas.
In its preliminary report based on the short field inspection by the team, the GSI, going by reports that the water level was more or less same in all the shafts present in the area and the level of the river nearly 10 to 11 metres higher, said since the water level is different in the river and in the adjoining shafts “it is ruled out that the river is contributing to the lateral seepage through the rock formations from any nearby location.”
It suggested that the probable reasons of the continuous recharge of these shafts, including the main shaft where the 15 miners are believed to be trapped since December 13, has to be explored by conducting detailed geological/geophysical investigations.
The GSI team after the preliminary reconnaissance of the area arrived at an opinion that a location in the bed of the river needs to be searched for probable seepage. “The continuous recharge in the shaft/s may be from some highly pervious zones like fracture zone or limestone caverns present at similar water level in the river bed. It may also be possible that the miners might have punctured a confined aquifer at that depth while excavating the coal,” the report said.
It further said that if the contention of the GSI team could be validated in the field, then remedial measures would be required to seal such zones to check the ingress of water, which is suspected to be continuously recharging the nearby shafts, “and it will certainly be helpful in successfully bringing down the water level in the main shaft by pumping out operations which may ultimately lead to success in the rescue operation.”
The team had held detailed discussions with scientists and representatives of National Institute of Hydrology, Roorkee, National Geophysical Research Institute, Hyderabad, NDRF, Indian Navy and others.
The report said as per the information provided, it was understood that the depth of the shaft, where the miners are trapped, is about 115 metres from where the horizontal drives for rat-hole mining proceeded in at least four directions.
“Based on the available geological data of the area, it was found that the shaft had been dug from upper limestone bed exposed along the back-slope of the shaft and excavated almost up to the top level of lower limestone bed. The coal seams that are targeted by the locals in this part by rat-hole mining occur in the middle sandstone member which rests between upper and lower limestone beds”, the report said.
