CHEMICAL CHARACTERIZATION OF GROUNDWATER SEDIMENTARY BASINS: THE CASE OF THE WATERS OF THE AQUIFER OF THE CONTINENTAL TERMINAL OF THE TOWN OF ABOMEY-CALAVI (BENIN

We conducted from March to June 2014 a study that focuses on the chemical characteristics of the wells water in the town of Abomey-Calavi. This work required sampling campaigns, and the statistical analyzes of the measurement results. Thus we found that the water studied is mainly acid. The most abundant ions in these waters are generally chlorides and sodium ions. These ions come from seawater intrusion, base exchange related to clay minerals that fix the calcium in the water after release of sodium and masses precipitating steam mainly original oceanic rich in Na+ and Clfrom the evaporation of sea water. The facies of studied waters is chlorinated potassic sodic. These water present an abundance of iron and nitrate which certainly come from surface (respectively, soil and wastewater). These high levels of iron and nitrate have disadvantages on the potability of water and justify the abandonment of certain drilling by the population. Thus do we see in the waters studied high levels of dissolved CO2. This demonstrates that the water circulate in open system relative to CO2. The pHeq = f (pHreal) diagram shows that these waters are all aggressive. The diagram ISD = f (ISC) indicates that the aquifer waters of the continental terminal of the town of Abomey-Calavi are relatively recent. They have a short residence time and a high circulation velocity.