Hydrogeophysical Evaluation of Groundwater Potential of Southwestern Part of Ilorin, Kwara State, Southwestern Nigeri

Groundwater potential evaluation study was carried out in the southwestern part of Ilorin metropolis which lies within the Precambrian Basement Complex of Nigeria using hydrogeophysical exploration method. As a result of inadequate potable water supply in the study area due to ever increasing population in Ilorin from 777,667 in 2006 to 893,304 in 2017. Which led to high withdrawal of groundwater and low productivity of many boreholes during the dry season. This research attempted to study the lithological characterization, possible groundwater water potential zones, overburden thickness, and rock types in the study area. The methodology involved desk study, field investigation and interpretation of all acquired data's in respect to the geologic information acquired in the proposed study area. Hence, Forty two Vertical Electrical Soundings (VES) were carried out across seven profiles in the area using the Schlumberger electrode array configuration, with current electrode separation (AB/2) varying from 50m to 150m. The interpretation of the VES data assisted in the characterization of three to five geo-electric layers from which the aquifer unit was delineated. The geo-electric sections obtained from the sounding curves revealed 3-layer, 4-layer and 5-layer earth models respectively. The 3-layer model with 46.34% (percentage) of occurrence, the 4- layer (43.9%) and 5-layer (7.32%) models show the subsurface layers categorized into the topsoil, sandy-clay/clayey-sand, lateritic clay, weathered basement and fresh bedrock. The weathered and fractured basement are the aquifer unit delineated across the area. The thickness of the weathered basement unit varies from 5.3m to 32.8m in the area. On the basis of geo-electric parameters the study area was zoned into high, intermediate and low groundwater potential zones.