ENVIRONMENTAL EFFECTS OF URBANISATION ON GROUNDWATER RESOURCES IN PARTS OF MINNA METROPOLIS, NORTH-CENTRAL NIGERIA

ABSTRACT

A study on the geology and hydrogeology of part of Minna Sheet 164NE was conducted with the aim of establishing the groundwater potential and control mechanism. Minna lies along longitude 6°30′E and 6°32′E and latitude 9°37′36′′ N and 9°39′34.5′′ N covering a total area of 14 km2. The area has a high population most of whom depends on groundwater for domestic uses. Geology of the area was studied on a scale of 112,000 using traverse method. Structural disposition of outcrops was established and positions taken. Thin sections of representative rock samples were made and analysed using petrological microscope. Groundwater inventory consisting of well locations, including borehole depth, water level and yield were taken. Samples of the water were obtained and analysed for physical and chemical composition. 90% of the area is underlain by rocks belonging to the older granite suite of the Nigerian Basement complex system while the remaining 10% is underlain by schist. Joint direction is principally in the NNE-SSW. Thickness of the weathered rock is in the range of 5-10m. Wells have a mean depth of 5m and water level of 3.57m. Boreholes have an average depth of 134m and mean yield of 71.28m3/d(0.83lt/s). Groundwater potential map shows that the north-eastern part of the area has greater potential at shallow level while other areas have slightly lower potential. Regional groundwater flow is in the NE-SW direction. Groundwater has a mean pH of 7.3, Electrical Conductivity 637.5µS/cm, and temperature of 28.6oC. Parameters with higher concentration include chloride 82.35mg/l, bicarbonate 70.18mg/l, sodium 56.18mg/l and calcium 46.16mg/l, nitrate. Trace elements that occur in fairly high concentration include zinc 1.15mg/l, phosphate 0.81mg/l and fluoride 0.32mg/l. The water primarily plots as mixed calcium- magnesium-chloride water and secondarily as sodium-bicarbonate water. The heavy metals are considered as Potentially Toxic Elements (PTEs)