Tamonkem Adzeh Roger^1,, Kemgang Dongmo Tchouta¹, Mvondo Valentin Yvan Emmanuel², Iwoudam Maïvow Edmond¹, Ngounou Ngatcha Benjamin¹

The hard rock-aquifer system in the urban context of Ngaoundere was investigated using piezometric measurements and hydro-chemistry to enhance understanding of its functioning and assess groundwater suitability for drinking and domestic purposes. Seasonal and intra-seasonal piezometric monitoring was conducted in different localities, along with chemical analysis of thirty-five ground and surface water samples. The chemical composition was determined for major elements was determined using ion chromatography, and water facies and mineralization processes were assessed using Piper and Gibbs diagrams. The water quality index (WQI) was calculated to evaluate groundwater suitability for human consumption. The findings revealed diverse piezometric behaviors depending on well/borehole geomorphological positions and seasons. Wells situated on hilltops exhibited high piezometric fluctuations, while those in valleys near rivers showed low fluctuations due to support from river water levels. Recharge occurred during the rainy season through direct infiltration from hilltops, with stream water levels influencing piezometric levels in surrounding wells and boreholes. The surface and ground waters exhibited low mineralization, characterized by calcium-magnesium bicarbonate and sodic-potassic bicarbonate facies. Water-rock interactions and dilution with rainwater were identified as the main processes controlling water mineralization. According to the WQI, all groundwater samples were classified as "excellent quality water" for human consumption. However, the microbiological quality of groundwater in and around Ngaoundere was influenced by human activities, making it unsuitable for drinking without treatment.

hard-rock aquifer, hydrodynamic, water-mineralization, water-quality, Ngaoundere