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-level were 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 of biotite, 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 1.2 m to 55.4 m with most of the wells falling between depths of 3.2 m – 7.7 m. Depth to water (DW) ranges from 0.4 to 52.2 m, with the water column (WC) falling between 0.3 m and 3.2 m. Water level elevation (WLE) which defines the hydraulic head in the area ranges from 1528.3 m to 1585.8 m. Groundwater flows 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 further show that the physical and chemical parameters of the groundwater are all within the permissible limits of 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.