DIMAPUR | JAN 7, 2015:
There has been an adverse effect on lives of fish and aquatic animals in four districts of Nagaland -- Mon, Longleng, Mokokchung and Wokha, where more than 48 coal mines sites have been under operation for more than nine years. According to a report prepared by Nagaland Pollution Control Board (NPCB), the acidic water and high sediments level 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.
The changes destroy the habitat of some of the valued species, and enhance habitat for less-desirable species, the report said. It may be mentioned that the major source of water pollution in coal mines is the carry-over of the suspended solid in the drainage system of the mine sump water and storm water drainage. The study found acidic water in the underground aquifers in some of the coal mines. In addition, waste water from coal preparation plant and mine are other sources of water pollution.
The report also said the acid mine drainage (ACD) is a metal-rich water formed from chemical reaction between water and rocks containing sulphur bearing minerals. The run off formed is usually acidic and frequently comes from areas where coal mine activities have rock containing pyrite, a sulphur-bearing mineral. However, metal rich drainage can also occur in mineralized areas that have not been mined. AMD is formed when the pyrite reacts with air and water to form sulphuric acid and dissolved iron. This acid run off dissolves heavy metals such as copper lead, and mercury into ground and surface water. This toxic water leaks out of abandoned mines contaminating ground water, streams, soil, plants, animals and humans. As a result, an orange colour of mixed chemicals derived from coal mining areas blankets the river, estuary or sea bed killing plants making the surface water undrinkable. These heavy metals are linked to serious health problems including an increase in birth defects.
Further, the survey report pointed out that coal mining consumes, diverts and dangerously pollutes local water supplies through the dumping and leaking of toxic wastes. This contaminates rivers, streams, underground water and soil threatening the lives of animals and human.
The impact of pollution still continues even after closing of mine in several sites. The high risk period for water contamination from coal mines occurs in the post-mining phase, when water pumping and treatment of the abandoned mines are left to flood. It may take several years or decades for new water cycle to re-establish at the mine site, and the time AMD occurs, the mine operation and regulations are no longer monitoring.
Moreover, ground water pollution may 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. This mine drainage can come from pits, ponds, or from rainfall infiltration and ground water flow during mining and after reclamation. Ground water pollution would result from the same toxic overburden and coal minerals that cause surface water contamination, the report also said.
On the other hand, indirect degradation of ground water would result from blasting which causes a temporary shaking of the rock and results in new rock fractures near working areas of the mine.
Blasting also causes old pre-existing rock fractures to become more open or permeable, by loosening mineral debris or cements in these fractures, this would affect nearly vertical leakage of ponded mine drainage from abandoned deep mines to underlying aquifers. The deep mines could be situated in the same coal seam being surfaced mined or in lower coal seam. Increased runoff of poor-quality water and erosion from soil piles, Recharge of poor quality water to shallow ground water aquifers, poor quality water flows to nearby seams, it added.
(Source: http://www.nagalandpost.com/)