Investigation of seasonal variation of groundwater quality in Jimeta-Yola area northeastern Nigeria

Seasonal variation of groundwater quality in Jimeta-Yola area was investigated using selected chemical contaminants. The results indicated that pollutant loading occurred in the dry and rainy seasons. The groundwater is fresh and varied from slightly acidic to alkaline in both the dry and rainy seasons. The mean values of BOD, COD and chloride exceeded the recommended standards of drinking water quality in the rainy season from the shallow and deep aquifers (hand-dug wells and boreholes). Nitrate and ammonium ion mean values in both seasons in shallow and deep aquifers exceeded the recommended limit of WHO. The mean coliform number counts exceeded the WHO recommended limit in both seasons in shallow and deep aquifers. The spatial distribution of EC and TDS reveal that the leachates from the dumpsites are significant source of groundwater contamination. The variation in contaminantdistribution is influenced by depth to water and well depth. There were increase in COD, BOD, nitrate, phosphate and chloride, and decrease in ammonium ion and coliform with water depth in shallow aquifer in the dry season, and COD, nitrate, ammonium ion, phosphate and chloride increase with water depth, and decrease in BOD and coliform in therainy season. COD, ammonium ion and chloride increase with well depth, and decrease in COD, BOD, nitrate, phosphate and coliform in deep aquifer in the dry season while COD, BOD, nitrate, ammonium ion, phosphate and chloride decrease in the rainy season. Coliform showed no depth control during the same period. In the dry season in leachate samples, contaminants revealed perfect correlation and nearly perfect correlation in the rainy season. The contaminants in all the aquifers revealed strong positive correlations in both seasons which are an indication of common source. Factor analysis indicates that groundwater chemistry is controlled by anthropogenic activities, salinity, ammonification and natural mineralization. It is recommended that safe waste disposal practice should be encouraged and drilling of boreholes to deeper levels is also suggested.