Iron in shallow ground water in Moro area, Kwara state, Nigeria

Hydrochemical analyses and a study of shallow ground water (basement aquifer) from several boreholes in the Moro area (UNICEF-assisted water project) have been carried out. The occurrence of relatively high iron content above the normal permissible level in relation to incrustative and/or corrosive potentials of the water are highlighted. Chemical analysis results indicate a predominantly Ca-HCO3 wafer type with low TDS and hardness. The interplay of high iron concentration (0-8.0 mg/l), mostly derived from the lateritic overburden materials, together with CO2-charged precipitation, and dissolved oxygen, as well as relatively high saturation indices with respect to siderite are thought to promote incrustative and/or in same cases possible corrosive characters of the ground water - thus the reported damage to riser pipes in the study area. Possible models of the observed incrustation presented are attributed to the interplay of oxidation of the ferrous ions and subsequent precipitation of Fe(II)-hydroxide and in some cases siderite. The corrosion process, on the other hand is insignificant, possibly limited to acid-attack/dissolution induced by CO2-charged precipitation recharging rite system. In general, the ground water in the study area could be regarded as potable and suitable for some domestic or agricultural uses. The high iron content in some locations suggests the need for some treatment and the measure recommended in this study.