BOREHOLE LOG CORRELATION AND GEOCHEMISTRY AS TOOLS IN DETERMINING RECHARGE ZONES TO THE MIDDLE ZONE AQUIFER OF THE CHAD FORMATION IN THE NIGERIAN SECTOR OF THE CHAD BASIN

Abstract

The continuous decline in hydraulic head of the Middle zone aquifer of the Nigerian sector of the Chad Basin and
the increasing water demand by human and animals necessitated a study of the recharge and flow direction of the
aquifer. In this work lithologic correlation and geochemistry are used as tools. The lithologic correlations of the
Middle zone aquifer indicate possible linkage of the aquifer with the overlying Upper aquifer at the southwestern
fringe near Damboa. The chemistry of the water samples indicates that the concentration of most of the elements
increases in the direction towards the Lake hence pointing at the southwestern fringe to be a recharge zone. The pH
and EC of the water samples were determined with a Combo pH/EC meter. Sodium, potassium, calcium and
magnesium ions were determined using Perkin Elmer Analyst 400 Atomic Absorption Spectrometer (AAS). The
anions of sulphate were experimentally determined by Lamda 35 Ultraviolet Visible Spectrometer and amount of
chloride and bicarbonate ions were determined by titration. The aim and objectives of the research is to determine
the recharge zones and flow direction for the Middle Aquifer using boreholes logs of 1960-2010 in addition to their
water samples analysis. Different authors gave divergent views on whether recharge into the Middle aquifer is
taking place or not. This issue is the main problem to be tackled. This will facilitate proffering solution to its
sustainability, realizing that the Middle Aquifer is the most extensive and most exploited of all the three known
aquifers in the Chad Formation to date. The major limitations of this study are that: The work relies on existing
boreholes as cost of drilling new ones for this study is prohibitive and hence based on locations of existing
boreholes.