Impact of Surface Runoff from Opencast Coal Mines in the Ib Valley Basin and its Management

Abstract

Energy is needed for economic growth,for improving the quality of life and for increasing opportunities for development.Most of energy requirement is fulfilled by coal,accounting for nearly 60% of the commercial energy demand of our country.Nearly 86% of these coals are obtained from opencast coal mines,which occupy very large areas.Opencast coal mining activities are known to cause serious environmental pollution if proper preventive and control measures are not adopted.Contamination of surface water bodies due to surface runoff in monsoon is one such concern.In this work,an attempt has been made to assess the runoff generated during monsoon in the Ib valley basin, which hosts some of the major opencast coal mines of the country.The Ib river valley is endowed with a very rich coal field known as Ib Valley Coalfield,which is a part of large synclinal Gondwana basin of Raigarh-Himgir and Chhattisgarh coalfields,and constitutes the south-eastern extension of the Sone-Mahanadi master basin.There are five opencast coal mines in this basin viz.Lajkura, Samaleswari,Belpahar,Lakhanpur and Lilari OCP, which come under Jharsuguda district in the state of Odisha.During monsoon season,rain water falls in the entire quarry area, external OB dump,coal stock and siding etc.in the entire coal field.The runoff flows into or out of the mine depending upon its topological profile.The surface runoff of the region takes its natural course flowing through the OB dumps,coal stocks,workshops and railway sidings into the surrounding water bodies which finally meet with Ib river. The Ib River flows from north to south and finally drains into Hirakud reservoir.This water often contains high load of total suspended solid(TSS),total dissolved solid(TDS), and heavy metals,which contaminate the surface and ground water.Sometimes it is acidic in nature and pollutes the water regime if the coal seam contains high amount of pyritic deposit.Therefore,the quantification of surface runoff from the coalfield and the study of its impact are very significant in order to formulate an appropriate management strategy.The present work deals with estimation of the runoff quantity during the monsoon season in a GIS interface.The surface runoff generated within the mine area and the sump capacity has been estimated by rational method.Visual interpretation of the DEM and flow direction maps generated in a GIS interface has helped us in understanding the behavior and direction of surface runoff because of the region’s topography.It was found that Lajkura and Samleswari OCP have adequate sump capacity to store the surface runoff generated during the monsoon. However,the other opencast projects do not have the storage capability to store the surface runoff within the mine premises.These mines need to create additional sumps; otherwise,sedimentation ponds of adequate dimension are required so that the suspended particles could be settled before the runoff is discharged to outside the mine boundary.
Additionally, water quality analysis was carried out to ascertain the quality of water within the mines as well as in the nearby areas. A number of water samples were collected from mine sumps, treatment plant inlet and outlet, mine discharges and nearby water bodies for the pre-monsoon and monsoon period. Analysis for Physical, chemical parameters and heavy metal content was carried out following the standard method given in APHA, 2012 and as per the CPCB guidelines. In general, the water quality of mine sump in most of the opencast mines are found to be within permissible limit for utilization in industrial activities like dust suppression, firefighting, irrigation of plantation, washing of HEMMs etc. It has been observed that there is increase in concentration of parameters like TSS, Oil and Grease in water samples collected in the monsoon season compared to the premonsoon quality. Most of the mine sump water is nearly neutral to alkaline in nature. However, the mine water of Lajkiura sump and Samaleswari south sump show strongly acidic characteristics. In most of the samples, the heavy metal concentrations are within the permissible limit as compared to effluent standards prescribed under Environment Protection Rules, 1986. But high concentration of selenium has been observed in some of the water samples, which have several health impacts on the human beings, animals as well as aquatic life. It is expected that the outcome of the study will help the mine management to formulate an appropriate strategy for control of surface runoff generated during the monsoon. This will help to avoid the surface runoff being discharged to the nearby areas and their probable contamination. Moreover, there is huge water demand in the mining area to fulfill the daily requirement during non-monsoon period. Thus, with adoption of proper management strategy, the runoff generated during the monsoon could be stored within the mine premises and used throughout the year. The water could also be supplied to nearby areas for irrigation of agricultural land in the dry seasons. If possible, it can even be used to supplement drinking water with some treatment.