摘要：Analytical results of thirty-seven water samples revealed that pH of the water samples ranged from acidic to alkaline throughout the sampling period. EC and TDS mean values were higher in the dry season in shallow aquifer and low in deep aquifer in the rainy season. This is an indication of the addition of leachable salts following the dissolution of waste materials in shallow aquifer. The low mean values of Ec and TDS in the case of deep aquifer is an indication of dilution effects due to recharging groundwater. The dominance of the cations in both seasons in shallow and deep aquifers was in the order of Na > Ca > K > Mg while the anions was in the order of Cl > HCO3 > NO3 > SO4 in both seasons in shallow aquifer and in deep aquifer in rainy season, and the anions was in the order of HCO3 >Cl>NO3> SO4 in the dry season in deep aquifer. The plots of log TDS against Na+ /(Na+ + Ca2+) indicated that most sample points plot in the region of rock dominance and weathering zone suggesting precipitation induced chemical weathering along with dissolution of rock forming minerals. Piper plots of the groundwater samples in the dry seasonin shallow aquifer classified the water types into Na-SO4-Cl, Ca-Mg-HCO3, Ca-Mg-SO4-Cl and Na-HCO3 water types while the sample plots indicated Na-SO4-Cl and Na-HCO3 water types in shallow aquifer in the rainy season. The plots of the samples indicated Na-HCO3, Ca-Mg-HCO3, Na-SO4-Cl and Ca-Mg-SO4-Cl water types in deep aquifer in both seasons. Cation exchange, salinisation and mixing processes were the processes responsible for the chemical evolution of groundwater in the area. Organic decomposition, sewage effluent and house hold solid wastes were themajor sources of nitrate in the area. It is recommended that controlled waste disposal practice should be encouraged while drilling of productive boreholes to deeper levels is also encouraged.
