Origin of Dissolve Ions in Groundwaters in the Northern Densu River Basin of Ghana Using Stable Isotopes of 18O and 2H

Stable isotopes of oxygen-18 and deuterium content in groundwater, surface water and rainfall in the northern part of the Densu river basin were studied with the main aim of identifying the origin and sources of ions in the groundwater in the area. The conversion of stable isotopes to d-excess was also exploited as a complementary tool to understand the processes of recharge. A comparison of the isotopic data with the rainfall, Local Meteoric Water Line (LMWL) and Global Meteoric Water Line (GMWL) indicates that the groundwater in the study area is mainly meteoric with few groundwater and all the surface water showing an evidence of evaporation. The study has also shown that, mineral dissolution from the geology is the main factor controlling the chemistry of the groundwater with evaporation having a minimal effect. The d-excess values show that the groundwater has undergone dilution with the rainfall and this is observed from the decrease of the d-excess of the groundwater with increase in Oxygen-18. This observation also suggests a modern day recharge to the groundwater.

Hydrogeochemical and Groundwater Quality Studies in the Northern Part of the Densu River Basin of Ghana

Agriculture, rapid urbanization and geochemical processes have direct or indirect effects on the chemical composition of groundwater and aquifer geochemistry. Hydrochemical investigations which are significant for assessment of water quality have been carried out to study the source of dissolve ions in the groundwater in some rural communities in the northern part of the Densu River basin. Twenty six samples comprising of twenty one boreholes, one hand-dug well and four surface waters were sampled for this study. The samples were analyzed in-situ for pH, Conductivity and salinity using a Hach potable meter, bicarbonate using a digital titrator. Major ions such as Na+, Ca2+, K+, SO42-, NO3-, Cl- etc were analyzed using ion-chromatography, flame photometer and Atomic Absorption spectrometer. The results showed that the groundwater in the study area are fresh and low in TDS (49.5-361 mg/l) and generally mildly acidic to alkaline (pH 5.57-7.48). The ground water quality of the study area are suitable for domestic purposes, since most of the parameters measured were within the WHO recommended values for drinking water, with the exception of nitrate (NO3--N which showed an elevated concentration in most of the samples (about 60%). Higher concentrations of NO3-, Cl-, SO42- etc were observed at the middle portion of the basin where there is extensive agriculture and rapid urbanization. The Piper diagram shows three major water types namely Na-Cl or Na-HCO3-Cl, Na-Mg-Ca-HCO3 and Na-HCO3 water types and Ca-Mg-HCO3 as minor about (8%) which are moderately mineralized. Ion-exchange, Weathering, Oxidation and Dissolution of minerals were found to be the major geochemical processes governing the groundwater evolution in the study area.

Hydrochemical and Isotopic Characterisation of Groundwaters in the Eastern Region of Ghana

Major ions and stable isotopes of groundwater in the Cape Coast granitoid complex (G1) and Lower Birimian (LB) formations in the Eastern Region of Ghana were evaluated to establish the source of recharge to the groundwater system. Five major hydrochemical facies were identified in the various rocks in the study area. They are calcium-magnesium-bicarbonate, sodium bicarbonate, sodium chloride and calcium chloride waters and mixed or non dominant water type. Sodium chloride and calcium chloride waters dominate aqui-fers of the Cape Coast granitoid complex whereas calcium-magnesium-bicarbonate is the dominant hydro-chemical facies in the Lower Birimian aquifers. The most probable geochemical process responsible for the evolution of these hydrochemical facies is dissolution of minerals in the various rock types. Stable isotope composition of the groundwaters established that the recharge to the groundwater system is derived from rainfall.