Water Resources Assessment Associated with Lignite Operations in Thar, Sindh, Pakistan

Major lignite deposits, all over the World are associated with unconfined and confined aquifers. This creates hydrogeological issues with a range of operational, safety and environmental problems associated with lignite mining. Ground water and surface water create a range of problems in lignite mining utilizing surface mining methods. The paper discusses a method of ground water control in a multi-aquifer environment in mining lignite using borehole pumps to dewater the mining operations. The technique will increase the slope stability and will present environmentally friendly solutions. The paper describes a proposed solution for the Thar lignite deposit in Sindh, Pakistan that has total reserves of 192 Bt. The water extracted for safe and economic mining operation can be used after treatment to provide a beneficial water regime to support human and agricultural development in an extremely arid climate. The paper also presents a proposed method of dewatering the Thar prospect together with an assessment of the quality of aquifer water. A series of boreholes were drilled to intersect lignite seams and surrounding aquifers to obtain water samples to determine their physical and chemical characteristics. The ground water assessments indicated that the saline water can be classified as brackish water with total dissolved solids contents ranging from 1000 to 20,000 mg/L, containing sodium and potassium chloride water. This water could be treated for industrial or agricultural purposes and for carrying out mining operations and supporting local inhabitants because it does not contain heavy and toxic metals such as arsenic, lead, mercury, or cyanides. However, results indicate that groundwater from a few locations contained traces of silver <4 ppb and zinc <0.1 ppm.