This study of the gneiss-fractured-rock aquifer in
Yaoundé capital of Cameroon determines: the aquifer setting-flow systems, the aquifer type, seasonal variations
in rock-water interactions, evolution of the hydrogeochemical processes,
physicochemical parameters and the suitability for domestic-agro-industrial use
of the groundwater. Physicochemical field tests were carried out on 445 wells
during four seasons for EC, pH, TDS, Temperature and static water level from
July 2016 to May 2017. 90 well samples were analyzed 45 samples per season: wet/dry. 38 borewell logs were used together with structural data to determine the aquifer setting. The field
physico-chemical and laboratory analysis data of well samples were
mounted unto various GIS software platforms: Global mapper, AqQa, Aquachem, Rockworks, Logplot7, Surfer and ArcGIS,
to get indices/parameters/figures, by use of Durov’s, Piper’s and Gibbs diagrams, Water quality index WQI, USSL ratio, Sodium Absorption
ratio SAR, Percent sodium %Na, Kelly Ratio KR, Magnesium Absorption Ratio MAR,
Total Hardness TH, Residual Sodium Carbonate RSC and Permeability Index PI that were determined. The process of groundwater ions acquisition is three-fold: by recharge through atmospheric precipitation, by ion exchange/simple dissolution between the rock-groundwater and by groundwater mixing in
its flow path. Water types are Ca-HCO3, Mg-HCO3 and Mg-Cl
while hydrogeochemical facies are Ca-Mg-HCO3 and Ca-Mg-Cl-SO4.
Most water samples are fresh, potable and soft all seasons. The hydrogeological
conceptual model is that of a three-layered single phreatic fractured-rock-aquifer
while other researchers postulated a two-aquifer, phreatic and semi-confined, two-layered model.