SOURCE:

Faculty: Physical Sciences
Department: Applied Geophysics

CONTRIBUTORS:

Obasi P. Njoku
Odoh, B. I
Akudinobi, B.E.B

ABSTRACT:

Hydrogeological and geochemical assessment of the lead – zinc mining areas of Abakaliki, Ebonyi State was carried out with emphasis on the quality status of available water supply sources, agricultural soils, geohydrological studies, aspects of the physical environment and socio- environmental implications of mining activities. A total area of about 794.2 km2 was assessed, with major communities covered including Enyigba, Mkpuma Akpatakpa, Ameka, Amorie, Amanchara and Alibaruhu where active and abandoned mines are located. One hundred and sixteen water samples, comprising forty – seven from groundwater sources and sixty- nine from surface water sources were analysed using Atomic Absorbtion Spectrophotometric and Ultra Violet / Visible Spectroscopy. One hundred and sixteen soil / stream sediments were collected and subjected to geochemical analysis using Atomic Absorbtion Spectrophotometric method, and pedologic safety analytical tools including Effect Range Low (ERL), Effect Range Median (ERM), Pollution Index (€), Geoaccumulation Index (Igeo), Contamination Factor (Cf), Pollution Load Index (PLI), and contamination degree were used to assess the impact level of mining activities in arable soils. One hundred and ten hand dug wells were sampled for geohydrological studies while surface geological mapping (including the studies of rock types and fracture pattern) was done. Geological mapping and studies of rock types show that the area is underlain by shales, mudstone and thin beds of sandstone and limestone. These shales are deeply jointed and fractured, and form a semi – confined aquifer which is the major aquifer in the area. The trend of fracture system is predominantly NW- SE. This controls the groundwater flow and hydrothermal mineralization of the area. Groundwater flow studies reveal predominance of recharge area in the central part which include Abakaliki Metropolis, Agbaja and Isieke, while the Enyigba, Ameka, Ikwo and Amanchara axis forms the discharge areas. Geochemical assessment of soils and stream sediments using six different pollution indices showed high degree of contamination for Ag, As, Pb, Hg and Cd (in the order of increasing pollution indices). This implies that arable soils around the mining areas are not suitable for food crop production as biomagnification can occur in the food chain. Assessment of contamination degree show higher contamination degree for the Mkpuma Akpatakpa and Ameka areas than the Enyigba and Amanchara areas. Results of hydrochemical analysis revealed that Ca2+, Mg2+, Fe2+, K+ ,Na+ (cations) and Cl-, SO42-, NO3-, HCO3- (anions) are the major hydrochemical constituents, while Al3+, Mo2+, Pb2+, Cu2+, Hg2+, Cr3+, Ni2+, Cd2+, Ag+ and Mn2+ are the trace constituents. pH values indicate acidic to basic water (3.67 – 10.68), while electrical conductivity, turbidity, Total Dissolved Solids (TDS) and temperature are within the limits of World Health Organization guidelines for drinking water. Concentrations of Cl-, SO42-, CO32-,Fe2+, Mn2+, Pb2+, Cr3+, Ni2+, Cd2+, Ag+, are above the recommended standard for drinking water, especially in areas close to the active mines. However, the Ameka and Mkpuma Akpatakpa mining areas recorded higher concentrations of the hydrogeochemical constituents. The trend of these hydrogeochemical attributes follows the NW – SE fracture system of the rocks of the area. There is aerial variation between the mining areas and other areas in the dissolved chemical constituents. Seasonal analysis shows a decreased concentration of chemical constituents in the rainy season relative to the dry season. The adverse socio – environmental implications of mining in the area includes destruction of vegetation, badland development, pollution, ecological disturbance system, destruction of buildings and health hazards.