GEOHYDROLOGICAL AND RESISTIVITY STUDIES OF A LIMESTONE MINE IN r' COASTAL SAURASHTRA

Abstract

The present work embodies the details and outcome of the hydrogeological, geophysical and hydrological investigations carried out in an open cast limestone mine situated near Ranavav in the Saurashtra region of the State of Gujarat with the objective of studying the quantity of groundwater flooding. Geologically, the study area is comprised of sedimentary formations viz. Miliolite limestone of Pleistocene age on the surface underlain by gypseous clay, marl, grit and sand (Gaj formation) of Lower Miocene age which in turn is underlain unconfirmably by basalt (Deccan trap) of Upper Cretaceous to Lower Eocene age. Electrical resistivity imaging has been carried out in the mine area to ascertain the subsurface architecture which reflects a good co-relation between the observed and existing geological and geophysical attributes. Water samples were collected to perform the isotope analysis to establish the origin of the mine water which was found to belong to groundwater origin. Along with the above analysis, an ionic tracer (NaCl) was employed to find out the groundwater flow direction which was inferred to be towards south-west within the cavernous limestone aquifer. A layer of marl (calcareous clay) occurring beneath the Miliolite limestone was found to possess a laboratory permeability of lO to iO rn/day. Besides, ArcGIS tool was extensively used to digitize and work out the groundwater flow data collected from the site for computation of available groundwater resource in the mining area. As an outcome of the study, a pumping system has been worked out on the basis of yearly recharge of groundwater and the standing volume of water in the mine pits for efficient dewatering of the flooded mine. The study has brought out the intricate details of water flooding the limestone mine.