QUANTITATIVE EVALUATION AND HYDROGEOCHEMICAL PROPERTIES OF GROUNDWATERS FROM PRECAMBRIAN ROCKS OF SAN PEDRO AREA (SOUTHWESTERN CÔTE D’IVOIRE)

Abstract

San Pedro area covers 6,912 km² at southwestern Côte d’Ivoire. Its rural population returns to use surface waters for domestic and agricultural needs because of many drillings previously established were damaged. This study aims to contribute best knowledge of quantity and quality groundwater from basement aquifers of this area. Database includes monthly temperatures, rainfalls, outflows and groundwater samples. The calculation of pluviometrical indexes through reduced centered data led to identify climate variability. Recharge of aquifers was calculated by hydrological balance following Thornthwaithe and GR2M methods. Hydrogeochemical properties were determined through the calculation of ions exchange indexes and chemical classification with Korjinski and Riverside diagrams.

During last three decades (1977-2007), climate variability presented consecutively humid, dry and humid periods. Aquifers recharge was evaluated to 701 m³/ hectare and 1008 m³/ hectare respectively through Thornthwaite and GR2M methods. Surface and groundwater levels are influenced by climate variability. Groundwaters are healthy for drinking water and agricultural irrigation. Hydrolysis of primary silicate minerals is the major process of groundwater mineralization. Groundwaters develop stability with kaolinite. During interaction between groundwater and surrounding-rocks, waters exchange their ions Mg²⁺ and Ca²⁺.