Geology and Groundwater Quality Assessment of IDO/OSI Area, Southwestern Nigeria

Abstract

Detailed geological mapping of Ido area was conducted with a view to establishing the lithologic units and compiling a working geological map of the area. Also, water quality assessment, entailing the bacteriological and physico-chemical analyses, of water samples from 20 hand dug wells within the study area was carried out. The geological studies confirmed the area to be a part of the Nigerian Basement Complex with lithologic units such as migmatites, gneisses, charnockites and granites underlining it. The results of bacteriological analysis revealed that the hand dug wells are contaminated with faecal coliform and E-coli. The value ranges from 4-13 cfu/100ml which is beyond WHO recommended standard for drinking water. The results of physical parameters revealed that the water samples are colourless and odourless, with average temperature of 26.05⁰ C. The pH value ranges from 5 – 7.3, which was interpreted to be slightly acidic to neutral. The results of chemical analysis give values of cations and anions in the water  samples as follows (Ca²⁺ 2.83 mg/l), Mg²⁺ (26.99mg/l) , Fe²⁺ (8.48mg/l)  SO₄^2- (16.24mg/l) Na⁺ (8.5 cfu/100ml) Cl^- (1.655mg/l), andNO₃^- (0.026mg/l) .Other parameters determined include total hardness (33.8mg/l), calcium hardness (11.7mg/l), magnesium hardness (13.52mg/l), electrical conductivity (257.6us/cm), turbidity (2.7NTU), total dissolved solids (45.5mg/l). A comparison of the rock chemistry to the chemical parameters of the water showed moderate influence of bedrock on the chemistry of the water. In general, the parameters   are within the limit recommended by WHO. Nevertheless, because of the bacteriological contamination, it is advised that all hand dug wells in the area should be cased and fitted with necessary filter and screens, or  covered at all times, boiled or chlorinated to ensure safe consumption.

Keywords: Ido, Water quality,   Bedrock, Contaminants, Lithologic units