Groundwater quality variations in Precambrian hard rock aquifers: a case study from Kerala, India

P Nandakumaran,K Balakrishnan

doi:10.1007/s13201-019-1084-8

Abstract

Analytical data of groundwater samples collected from weathered and deep fractured zones in the Precambrian charnockite aquifers in Kerala, India, have been studied to understand their hydrochemical variations and reasons thereof. Concentrations of the majority of the constituents analyzed were found to increase with increasing depth of aquifers, with the exception of nitrate. Studies indicate that various processes such as ion exchange reactions, carbonate weathering and silicate weathering are active in both the aquifers which influence the hydrochemical composition of groundwater in them. The prevailing groundwater quality in the aquifers is dependent on the dominance of each process in relation to others. Principal component analysis of the data suggests that contamination from anthropogenic sources has a major role in determining the hydrochemical characteristics of groundwater in the weathered zone unlike in the case of fractured aquifers where water–rock interaction is the major factor responsible. The study also indicates limited hydraulic connection between the weathered and fractured aquifers at the local scale.

Highlights

Fractured hard rocks are important repositories of groundwater in many countries of the world
Based on the detailed study of hydrochemical data of groundwater samples collected from the weathered and fractured aquifers in the Precambrian charnockite aquifers in Kerala, India, it is observed that groundwater in both the aquifers is generally basic in nature and frequency distributions of the majority of constituents are positively skewed with significant deviation from normality
Study of cation dominance in the aquifers indicates more Na in weathered zone when compared to the fractured aquifers, likely to be due to factors such as anthropogenic input of common salt (NaCl) into the groundwater system, contribution from marine aerosols and reverse ion exchange reactions between Ca in groundwater with Na in the aquifer material

Summary

Introduction

Fractured hard rocks are important repositories of groundwater in many countries of the world. These rocks are exposed as outcrops in large areas of the world, covering more than 20% of the present land area (Krasny et al 2003). They are highly heterogeneous and anisotropic and represent complex hydrogeological environments. Characterization of groundwater quality and a comparative study of hydrochemical characteristics of groundwater in the weathered zone and deeper fractures in the Precambrian charnockite aquifers of Kerala, India, has been attempted in this paper

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Discussion

Conclusion