GROUND WATER POTENTIALS OF NUMAN AND ENVIRONS, ADAMAWA STATE, NORTH-EASTERN, NIGERIA

Numan town is situated along the confluence of rivers Benue and Gongola and is a road junction town about some 60 km west of Yola. Lithologic logs of 7 boreholes, field measurement data, stream flow and meteorological data and hydrochemical data generated from sampling and analysis of groundwater from 17 points (7boreholes and 10 handdug wells) were evaluated to establish the potentials of groundwater in Numan area. The area receives about 800mm of rainfall annually out of which 80% is lost through surface runoff and evapotranspiration while about 20% goes to recharge the groundwater system. Groundwater in the area is hosted in three aquifer systems all tapping from three geologic formations- the Bima Formation, the Yolde Formation and the Quaternary river course alluvium. Handdug wells tap their water from mainly the upper unconfined aquifer whose depth ranges from 0- 40m and the boreholes are completed in either the middle semi confined aquifer 40 -75m or the lower confined aquifer 75-240m (depth range of 0-240m). The computed aquifer parameters gave a mean hydraulic conductivity of 5.6 x10 -1m/day, a Transmissivity of 65.67m2/day groundwater velocity of 2.43m/yr, groundwater discharge of 612.69m3/yr, a groundwater reserve of 1.01x1010m3 which is capable of supporting a population of 1.4m for one year on an average of 220/l/day/head and a mean borehole yield of 20 m3/hr. Results of the hydrochemical analysis indicate that most of the water samples agreed with both the WHO 2006 and the NIS 2007 drinking water quality standards. However isolated samples especially from the upper unconfined aquifer tested moderately hard to very hard (106-421mg/L). Few cases of high NO3- (88-132mg/L) in HW6 HW10 HW11, high Fe2+ (1-2mg/L) in HW1 and HW2, were recorded. Two dominant water types were recorded; Ca2+-HCO3- (from four boreholes and seven handdug wells) and Na++K+-HCO3- (from three boreholes and three handdug wells). This study suggests that Numan and environs could be considered as a potential source of sustainable groundwater supply as a good alternative to the existing sources of supply. It would however require an improved waste management system and proper well completion methods to check the encroachment of surface generated pollution