Indices of SINTACS were used to analyze the aquifer vulnerability of the Lafia Formation aquifer (central Nigeria). The assessment of the aquifer vulnerability of the Lafia Sandstone aquifer is essential because the aquifer constitute the only aquifer in the region that supply the water demand of the region for all purposes. The urban area is growing and as such, more domestic and industrial wastes are generated which are disposed indiscriminately. Contemporaneously, agricultural activities are on the increase in the rural areas which generate agricultural wastes. The SINTACS model employs seven parameters (depth to water level, effective infiltration, unsaturated zone, soil media, aquifer media, hydraulic conductivity, and topographic slope), which were employed to produce vulnerability maps. The severe vulnerability index (VI) ranged from 139.79 to 209.19. The vulnerability mapping reveals that the water bearing formation is highly vulnerable in the central and southern parts of the area, which account for 27.98 percent of the total area. The medium vulnerability area encompasses approximately 46.23 percent of the region and is the most prevalent vulnerability class. 25.79 percent of the area around the northern part of the area accounts for low vulnerability. Nitrate concentrations measured in groundwater of the area compared significantly with the vulnerability zones classified by the VI. Parameters for the unsaturated zone and depth to water level imposed the largest impact on the VI thus, during groundwater development, wells should made to drilled to greater depths, wells should be concentrated in areas of low and medium vulnerability, and indiscriminate disposal of wastes should be discouraged.
Key words: Aquifer; GIS; Groundwater vulnerability; Lafia Sandstone; SINTACS; Sensitivity analysis