Study of coal mining areas in Nagaland and its impact on environment- Part III
Kohima | January 13
The Nagaland Pollution Control Board (NPCB) in a report has expressed concern at coal mining operations in Nagaland being a major source of water pollution.
Coal mining, being an environmentally unfriendly activity has attracted attention from the stand point of environmental impacts and their mitigation, the report titled ‘Study of coal mining areas in Nagaland and its impact on environment,’ said.
Mining, it stated affects all components of environment and the impacts are permanent/temporary, beneficial/harmful, repairable /irreparable, and reversible/irreversible.
The NPCB particularly pointed to the carry-over of the suspended solids in the drainage system of the mines. In some of the coal mines, acidic water is also found in the underground aquifers. In addition, waste water from coal preparation plants and mines are other sources of water pollution, it stated.
The report said that in Nagaland coal mining is done mostly in the hills except for some low lying areas bordering Assam. The excavated soil and coal residue in this terrain are left exposed and during rain, leaching takes place and the water containing SO2 gets into the streams thereby making the water acidic, affecting aquatic life and making the water unhealthy for consumption.
The Acid Mine Drainage (AMD), the NPCB explained, is a form of metal-rich water produced from the chemical reaction between water and rocks containing sulphur-bearing minerals. The runoff formed is usually acidic and frequently comes from areas where ore or coal mining activities have exposed rocks containing pyrite, a sulphur-bearing mineral.
This toxic water leaks out of abandoned mines contaminating groundwater, streams, soil, plants, animals and humans. The NCPB warned that these heavy metals are linked to serious health problems including an increase in birth defects.
Coal mining also consumes, diverts and dangerously pollutes local water supplies. It pollutes fresh water through the dumping and leaking of toxic waste. “This contaminate rivers, streams, underground water and soil, threatening the lives of animals and humans,” the report stated adding that even after a mine is closed, the impact of pollution still continues.
The high –risk period for water contamination from coal mines occurs in the post-mining phase, when water pumping and treatment of the closed or abandoned mines are left to flood. It may take years or decades for a new water cycle to re-establish at the mine site, and by the time AMD occurs, the mine operators and regulators are often no longer monitoring, it stated. The NPCB said that water pollution from mine waste rock and tailing may need to be managed for decades, if not centuries, after closure.
In addition, the NPCB stated that ground-water pollution can also occur both directly and indirectly as a result of surface mining. Direct degradation can occur to ground water situated downhill or down gradient from surface mine, by flow of contaminated drainage from the mine during mining and after reclamation.
Indirect degradation of ground water could result from blasting, which causes a temporary shaking of the rock and results in new rock fractures near working areas of the mine, the report stated. It warned that blasting can also cause old pre-existing rock fractures to become more open or permeable, by loosening mineral debris or cement in these fractures; this could affect nearly vertical leakage of ponded mine drainage from nearby abandoned deep mines to underlying aquifers.
The NPCB report cautioned of the varying effects that these sediments have on aquatic wildlife. High sediment levels can kill fish directly, bury sprawling beds, reduce light transmission, alter temperature gradients, filling pools, spread stream flows over wider, shallower areas, and reduce production of aquatic organisms used as food by other species. These changes, it lamented, have destroyed the habitat of valued species, and could enhance habitat for less-desirable species.