Hydrogeological and Hydrogeochemical Investigation of Shallow Groundwater in Gembu, Mambilla Plateau, Nigeria

Abstract

Hydrogeological and hydrogeochemical techniques were used to investigate shallow groundwater in Gembu, Mambilla Plateau, Nigeria.A total of ninety (99) nine hand dug wells were studied, where their geographic location and ground elevation, well depth, depth to water-levelwere determined. Thirty three (33) representative samples collected from hand dug wells in the study area were analysed for their physico-chemical characteristics. Standard field and laboratory procedures were taken in the collection and analysis of the water samples.The area is underlain by granitic rocks of two major varieties, biotite granite and alkali feldspar granite, composed mainly ofbiotite, orthoclase feldspar, quartz, hornblende and opaque minerals. Hydrogeological mapping carried out shows that the elevation of the wells above sea level ranges from 1529 m to 1592 m, while well depths (WD) range from 1.2m to 55.4m with most of the wells falling between depths of 3.2m – 7.7m. Depth to water (DW) ranges from 0.4 to 52.2m, with the water column (WC) falling between 0.3 m and 3.2m. Water level elevation (WLE) which defines the hydraulic head in the area ranges from 1528.3 m to 1585.8m. Groundwaterflows generally towards the eastern portion of the central part of the area, with localized minor low portions , representing local flow directions in western part of the area. The results furthershow that the physical and chemical parameters of the groundwaterare all within the permissible limitsof World Health Organisation (WHO) and Nigerian Standard for Drinking Water Quality (NSDWQ), with the exception of magnesium (Mg++) and iron(Fe++).Only two of the 33 wells had concentration of bicarbonate and phosphate above the permissible limits, hence the water is not considered safe for drinking. The dominant hydrogeochemical facies was found to be sodium-potassium-sulphate-chloride (Na-K+ SO42- + Cl-)type. The dominant process contributing ions to the groundwater in Gembu is rock: water interaction, with minor contribution of domestic effluents and vegetable farming within the metropolis.