Assessment of hydraulic connectivity among shallow and deep aquifers and surface water of Central Gujarat: An isotopic approach

Abstract

The primary objective of this study is to identify the surface water - groundwater interaction and interaction among groundwater at different depths using stable isotopes (δ18O and δ2H). The Fence diagram of the study area describes the subsurface geology where the main aquifer system includes both confined and unconfined in the VRB area and is complex multi-layered with different sources of recharge. The flow pattern of groundwater is generally from the highland of north-east to low-lying south-west of VRB and is indicated by the piezometric surface map of pre-monsoon, and post monsoon, 2016. The δ2H (‰ VSMOW) and δ18O (‰ VSMOW) values do not show any symmetric distribution among them. The values for shallow groundwater ranges between −23.0‰ and 1.9‰, and −3.2‰–2.3‰, respectively with a mean value for δ18O and δ2H are −1.26‰ and −11.194‰ respectively. The depth wise interpretation revealed that the locations Virpur and Nana Pura show connectivity. Therefore, deep and shallow aquifers are contaminated due to this connectivity. The plots of d-excess vs. electrical conductivity, d-excess vs δ18O and electrical conductivity vs. δ18O indicate that most of the groundwaters are primarily influenced by evaporation process, high mineral dissolution and enrichment of δ18O. The plot of δ18O vs. nitrate indicate the anthropogenic influences like agricultural activities in this region. The SI values of calcite and dolomite indicates oversaturated condition along with dissolution of these minerals in the aquifer matrix.