ENVIRONMENTAL HYDROGEOCHEMISTRY OF THE BENIN FORMATION OF THE PORT HARCOURT, ABA AND OWERRI AXIS IN THE NIGER DELTA, NIGERIA

Abstract

ABSTRACT

Soil and water pollution are major environmental problems facing many coastal regions of the world due to high population, urbanization and industrialization. The Environmental Hydrogeochemistry of the Benin Formation of the Port Harcourt, Aba and Owerri axis in the Niger Delta, Nigeria was investigated in this study. The study area lies between latitudes 440IN to 5º40IN and longitudes 6º50IE to 7º50IE covering parts of Port Harcourt, Aba and Owerri a total area of about 12,056 km2. Hydrogeological investigations show that the aquifers in the area are largely unconfined sands with intercalations of gravels, clay and shale. Results of geoelectric sections, boreholes logs and sieve analysis confirm the dominance of sandy horizons in the area. Pumping test results show that the transmissivity ranged between 152.0 m2/day and 2835.0 m2/day with an average value of 1026.0 m2/day while the specific capacity varied between 828.0m3/day and 15314.0 m3/day with a mean value of 6258.0 m3/day. Well discharge ranged between 1624.0 m3/day and 7216.0 m3/day with an average value of 3218.0 m3/day while hydraulic conductivity varied between 3.2 m/day and 478.4 m/d with a mean value of 98.6 m/day. These findings indicate that the aquifer in the area is porous, permeable and prolific in groundwater. The observed wide ranges and high standard deviations and mean in the geochemical data are evidence that there are substantial differences in the quality/composition of the groundwater within the study area. The plot of the major cations and anions on Piper, Durov, and Scholler diagrams indicated six hydrochemical facies in the area: Na-Cl, Ca-Mg-HCO3, Mg-Ca-SO4, Ca-Mg-Cl, Na-Fe-Cl and Na-Fe-Cl-NO3. Heavy metal enrichment index revealed 12 elements in the decreasing order of: Fe > Ni > Cu > Zn > Mn > Cd > V > Co > Pb > Cr > As > Hg. The study identified salt intrusion, high iron content, acid-rain, hydrocarbon pollution, use of agrochemicals, industrial effluents and poor sanitation as contributors to the soil and water deterioration in the area. Saltwater/freshwater interface occurs between 5 m and 185 m while iron-rich water is found between 20 m and 175 m. The first two factors are natural phenomenon due to the proximity of the aquifer to the Ocean and probably insitu weathering and mobility of marcasite, a sulphite mineral contained in the rock. The occurrences of the marcasite are localized at depths between 150m and 180m. The last four factors are results of various anthropogenic activities domiciled in the area. DRASTICA model, a modification of DRASTIC model was developed and used in the construction of aquifer vulnerability map of the area. Modern sanitary landfill that ensures adequate protection for the soil and groundwater was designed and recommended to replace the existing open-dumpsites. Owing to the monumental and devastating effects of hydrocarbon pollution in the area, the need to eradicate gas flaring and minimize oil spills in the area was advocated. Bioremediation and phytoremediation techniques were recommended to be applied in the clean-up of soils and water contaminated with hydrocarbon in the area. The efficiency of multivariate statistical techniques in evaluating hydrogeochemical data have been demonstrated in this study.