Hydrogeology And Ground Water Potentials Of The Pre-Cambrian Basement Rocks Of Tabe And Environs In Gwagwalada Area, Abuja North Central, Nigeria

Abstract

The hydrogeology and groundwater potentials of Tabe and Environs in Gwagwalada Abuja Nigeria were carried out using lithologic logs of 7 boreholes, field measurement data, stream flow / meteorological data and hydrogeochemical data. 17 sampling points (7 boreholes and 10 hand-dug wells) were evaluated to establish the potential of groundwater in the area. Annual rainfall in the area is 800mm and 80%of it is lost through surface runoff and evapotranspiration while about 20% recharges the groundwater system. The area exhibits four aquifer systems from four distinct geologic lithologies - weathered layer aquifer, weathered/fractured or partly weathered aquifer; fractured aquifer and the Quaternary alluvium.  Groundwater from the hand-dug wells is mainly from the upper unconfined aquifer with a maximum depth of about 25m, while the boreholes are completed either within the middle semi-confined aquifer 25 -45m or the lower confined aquifer 45-65m (depth range of 0-65m). The computed aquifer parameters gave a mean hydraulic conductivity of 5.60 x10^-1m/day, a transmissivity of 28.32m²/day groundwater velocity of 2.43m/yr, groundwater discharge of 612.69m³/yr, a groundwater reserve of 1.01x10¹⁰m³which 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 hydrogeochemical analysis indicate that most of the water samples are within 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); with a few cases of high NO₃^-(88-132mg/l), high Fe²⁺ (1-2mg/l). The area has two dominant water types, the Ca²⁺-HCO₃^- and the Na⁺+K⁺-HCO₃^-. The study reveals that the Gwagwalada area (Tabe and environs) could be considered as a potential source of sustainable groundwater supply and also 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 avoid surface contaminant migration to the groundwater.