Application of Environmental Isotopes in Elucidating Groundwater Recharge in Abuja, North-Central Nigeria

Abstract

The study area covers an area of about 5,000Kim" in the central part of the Federal Capital Territory, Abuja, Nigeria, stretching along a NE-SW axis, cutting across geological, geomurphological and geopolitical boundaries of the territory. The aquifer systems in the study area are formed by weathered and fractured basement except in the southwestern part, which is formed by the sandstones of the Bids Basin. Eleven groundwater and one rain water samples were collected and analyzed for stable isotopes of deuterium (H) and Oxygen-18 ("O) and radioactive isotope of tritium (IT), according to standard methods. Results of isotope analyses revealed that the measured & II values of the groundwater samples range from-17.1 10 -14.3%0 while that of & "O range from -3.53 to -2.59%n. The 8 H and 8 O diagram shows that the water types originated from precipitation as the samples plut around the Global Meteoric Water Line (GMWI) with a deuterium excess in the range of 102 2.7. This indicates similar recharge conditions and an isotopic enrichment by evaporation. Tritium (H) concentration for the groundwater samples varies from 2,3 to 5.0 TU with a mean of 3.56TU while that of the only rainwater sample was 4.85 TU. Applying qualitative age categorization, the range of tritium values depicts active recharge and recent groundwater.