Recharge mechanism and processes controlling groundwater chemistry in a Precambrian sedimentary terrain: a case study from Central India

Abstract

Unplanned and unsustainable extraction has created stress on groundwater resources in many parts of India. The stress symptoms are more pronounced in hard rock areas, where the aquifer potentials are comparatively low. Present research targeted an area of 3000 km2 in the interstream region between the Kharun and Seonath rivers, which is one such region in Central India. In spite of being a water-stressed area, so far, little is understood about processes of recharge, amount of recharge and processes controlling chemical quality, which are key inputs for groundwater management in the area. This study presents an appraisal of recharge mechanism, recharge rate and prevailing water–rock interactions in the study area. Stable isotope composition of groundwater when compared to that of rainfall indicates monsoon rainfall as the primary source of groundwater recharge. Winter rains, which are characteristically enriched in heavier isotopes, do not contribute notably to groundwater recharge. Recharge is rapid with minor or no evaporative enrichment before recharge. Further, analysis of stable isotopes show that ‘macropore recharge’ is dominant in limestone or calcareous shale, covering more than 70% of the study area. Also apparent is the vertical connectivity amongst the aquifers. However, active intermixing of surface water and groundwater is not a predominant process. Annual groundwater recharge from rainfall, as derived from chloride mass balance, is 105.26 million cubic metre. Groundwater is predominantly of bicarbonate type, irrespective of its hydrostratigraphic (lithology) setting. Dissolution of carbonates and gypsum (occurring as veins), weathering of feldspar and ion exchange of clay minerals are amongst the most likely processes controlling the regional groundwater chemistry.