Determination of ground water quality associated with lignite mining in arid climate

Ground water and surface water create a range of problems in lignite mining utilizing surface mining methods. In order to create a safe and economic mining environment, it is essential to carry out mining after dewatering the rock mass surrounding the lignite mines by advance dewatering techniques. This paper briefly describes the ground water regimes including pressure gradients associated with various lignite deposits together with the practical examples of some important lignite deposits in the world. An effective method of controlling ground water in multi-aquifer environment in lignite deposits is to carry out rock mass dewatering using borehole pumps. This approach will help reducing the inflow rates of ground water to the mining excavation and also increase the effective strength of the overburden strata, thus, increasing the slope stability of the mining excavations. The main theme of this paper is to present a case history analysis of Thar lignite deposit in Sindh, Pakistan which has lignite reserves of some 193 billion tonnes. The paper presents a proposed method of dewatering the Thar prospect together with an assessment of the quality of aquifer water which can be used to improve the quality of life of people inhabiting in the Thar Desert area of Sindh, Pakistan. Water samples from three aquifers were collected from nine different locations and were analyzed in the laboratory for evaluating their physical and chemical characteristics. The test results indicated that the aquifer water can be classified as (sodium+ potassium) – chloride type water with a TDS range of 1000 to 20,000 mg/L. Consequently, this ground water is classified as brackish (saline water) requiring treatment before it can be utilised for domestic or industrial consumptions. It should be noted that this ground water does not contain heavy metals and toxic metals including arsenic, mercury and lead or cyanide. However, results indicate that groundwater from a few locations contained traces of silver (