Ground water is part of the hydrologic cycle. Generally, ground water occurs in permeable geologic formations known as the aquifer. Before the exploitation of groundwater in a region, it is usually necessary to determine the hydraulic characteristics which allow the flow of water through the aquifer. The notable parameters are the hydraulic conductivity or permeability and transmissivity. Groundwater is a major source of water supply in most part of Nigeria including Ilorin, Kwara State. Data from pumping test carried out for drilled boreholes at different locations in the study area were collected from various agencies involved in water supply planning, exploration and development. The data consist of pumping test results, discharge, drawdown and geophysical and borehole constructional methods. The determination of the aquifer characteristics was based on the Theis Residual Recovery Method. The depths of the boreholes were found to range from 17 to 60 m with an average of 32.9 m while well discharge ranged from 0.24 to 2.5 l/s with an average of 0.89 l/s. The outcome of the analysis showed that the value of hydraulic conductivity ranged between 0.2 and 16.289 m/day with an average of 1.87 m/day and transmissivity ranged between 7.184 and 447.919 m2/day with an average of 49.12 m2/day. Maps showing the piezometric surface, the hydraulic conductivity and transmissivity of the aquifer in Ilorin have been developed. These can be used for the planning, site selection and drilling of wells in the area.
Key words: Hydraulic conductivity, transmissivity, Theis Residual Recovery Method.