Hydrogeological Issues Concerning the Thar Lignite Prospect

The paper is concerned with the hydrogeological appraisal of the proposed mining operations in the Thar lignite field in Sindh, Pakistan. The Thar coalfield covers an area of approximately 9000km2 and contains three lignite seams lying at depth of 130m to 250 m. In the Thar lignite field, the presence of three main aquifers induces pore pressure in the rock mass surrounding the lignite seams and makes high wall slopes potentially unsafe. It is, therefore, necessary to dewater the rock mass before commencing mining excavations. The paper describes the proposed mine dewatering scheme to facilitate depressurising of the rock mass surrounding the mining excavations. Inflow prediction of groundwater to the surface mining excavation was carried out using a SEEP/W finite element software package. The simulation results show that the ground water inflow from the Top aquifer is 114m 3/d, from the Intermediate confined aquifer is 141m 3/d and from the Bottom confined aquifer is 1.28 x 105 m3 /d. These results were compared with the analytical solutions which indicated that the relative error of estimation of inflow quantities varies from 3.4 % to 6.4%.