Radial anisotropy technique to target fractured aquifer in Precambrian Metamorphics: An exemplar from Eastern India

Abstract

Prospecting of groundwater in sub-surface horizons is a major challenge in Precambrian metamorphic terrains, e.g. the Purulia district of West Bengal, providing little scope for locating groundwater. However, detailed study of the Fracture-Correlated Lineaments (FCL) in variably fractured metamorphic terrains can give vital hydrological clue in selecting sites for tube wells with promising discharge of groundwater. This is an attempt to identify the hydraulically significant FCL using twin approach of surface geological investigation and radial anisotropic method. An integrated approach was adopted based on study of bedrock fractures, weathered-zone profiles, hydrological data with use of radial anisotropy method by Georient and Surfer softwares; revealing directional dominance of hydraulically significant FCL along 100–140°, concordant to regional foliation-trend of granite gneiss, and also along 15–40°, perpendicular to regional foliation-trend of phyllite, mica schist and epidiorite. The litho-stratigraphic preference of hydraulically significant FCL was found maximum for phyllite (38%) followed by mica schist (26%), epidiorite (21%) and granite gneiss (15%). The FCL pattern shows concurrence with thick weathered mantle, and high groundwater productive zones. The findings validate the usefulness of radial anisotropy as an important technique for identification of hydraulically significant FCL, and encourage their applicability in groundwater development in case of Precambrian metamorphic terrains.