Hydrochemical processes and groundwater quality in the basement-sediment aquifer of Lapai, central Nigeria

Sub-Saharan Africa countries, such as Nigeria rely heavily on groundwater resource to meet domestic, agricultural and industrial needs because of its sustainable nature, and growing demand fuelled by rising population explosion. Prior knowledge of groundwater evolution is significant for the preservation, and effective use of water resources, as such knowledge is scarce present in basement-sediment aquifers. To achieve this, the basement-sediment aquifers in Lapai, Central Nigeria were assessed for their geochemistry and hydrochemical processes using field, laboratory and statistical methods. Groundwater samples from fifty (50) locations were collected within the study area and analyzed for this purpose. Sampling was done during peak dry season such that minimal interaction with surface water is present in the aquifer. Physical (temperature, pH, electrical conductivity, total dissolved solids) and chemical (Ca 2+ , Mg 2+ , Na + , K + , HCO 3 - , Cl - , NO 3 and SO 4 2- ) parameters were considered for the investigation. Analysis and interpretation of the hydrochemical processes were done using hydrochemical modelling, bivariate plots and scatter diagrams. The study revealed dominant hydrochemical facies to be Ca-Mg-Cl (54%), Mg-Cl (32%) and Ca-Cl (14%) water facies. Silicate and carbonate weathering, as well as reverse ion exchange are the dominant hydrochemical processes regulating the groundwater chemistry in the groundwater from both basement and sedimentary aquifer. Oversaturation of carbonate minerals in the groundwater obtained from saturation indices modelling could lead to precipitation of carbonate minerals and co-precipitation of heavy metals from the aquifer at the right kinetic condition, leading to a reduction in heavy metals mobility and concentration. Assessment of the water quality suggest that the groundwater is generally suitable for consumption, although there is elevated nitrate above the WHO recommended limits in some of the samples (n=4) which signifies anthropogenic influence, requiring treatment before consumption