Seepage Modeling for a Large Open Pit Coal Mine in India

Medapalli Open Cast Project (MOCP) owned by M/s Singareni Collieries Company Limited (SCCL), Andhra Pradesh, India where “Highwall mining” is practiced lies in the immediate vicinity of a large perennial river, ‘Godavari’. The mine and river, which are only 140–150 m apart, an artificially constructed embankment, built above highest flood level, restricts the water leakages into the mine. A need to know seepages that may occur at active working faces of MOCP highwall mining faces, referred here as web holes/web cuts, is realized and this seepage modeling study is undertaken. Since the coal mine has “Barakar formations” which, in general, has watery field conditions, there exists an enhanced possibility of seepage or water inflow into the mine pit. For this reason also this predictive assessment study of seepage modeling became essential. The quantitative estimation of water is done by conceptualized model of mine which was based on the sub-surface geology and hydrological set up of the area. SEEP/W module of ‘Geostudio’ software is used for prediction, estimation and assessment of water flux, inflow and recharges quantities as it is capable to consider the saturated/unsaturated flow conditions for the encountered unconfined aquifers. In the modeling exercise, we used ‘steady state’ and ‘transient state’ conditions to determine the water quantities of the seepage faces at pit walls/web holes. The estimation so done for this coal mine is compared and verified by another popular “Ground water flow and contaminant transport and river modeling software” namely, MODFLOW. Briefly and concisely, this study concludes that the water seepage from river to mine pit is very less and hence it has no adverse effect on the web holes and web pillars of highwall mining faces. The results of this study had helped mine management in taking decision about (a) uninterrupted operation of ‘highwall miner’ at the coal extraction faces, (b) safe extraction of the locked in coal between river and mine, (c) developing and designing safe work places for both man and machinery, (d) achieving targeted coal production as per production schedule, (e) effective drainage and utilization of mine water as per the action plan of mine. Thus, on account of seepage water any harm/damage to already deployed, ‘highwall miner’ is very remote and the coal wining operation at MOCP is safe. The mine planning can be done easily using estimated water quantities and mine faces can be kept dry during maximum period in a year.