Hydrogeochemical Investigation of Groundwater Resources in Umunya and Environs of the Anambra Basin, Nigeria

摘要

The study area falls within the Anambra Basin in southeastern Nigeria. The lithostratigraphic units within the study area are the Imo Shale (Paleocene) and the Ameki Formation (Eocene). This paper takes a closer look at the physico-chemical analyses of the groundwater discharge from the prolific Nanka Sands reservoir.A total of twenty-one (21) water samples were obtained from the groundwater sources and were analyzed for their physico-chemical characteristics with the aim of assessing their quality and usability. Result of some physical and hydrochemical parameters show mean values of 5.75 pH, 46.98 mg/l TDS; 10.86 mg/l Ca~(2+) , 7.50 mg/l Na~+ ; 3.29 mg/l K~+ , 1.46 mg/l Mg~(2+), 25.74 mg/l HCO_3; 16.70 mg/l Cl~- , 0.09 mg/l Fe~(2+), 4.65 mg/l NO~(3-) and 72.36 μs/cm conductivity. The water hardness and Sodium Absorption Ratio (SAR) are respectively, 34.74 mg/l and 0.73. Statistical analyses, using the product moment coefficient of correlation, indicate very strong correlation between the following pairs of parameters: Total Hardness and TDS (r = 0.94); TDS and EC (r = 0.99); Ca~(2+) and HCO_3~- (r = 0.83); Ca~(2+) and Mg~(2+) (r = 0.70) ; Na~+ and K~+ (r = 0.57); pH and TH (r = 0.52) while negative correlation was observed between pH and Cl~- (r = - 0.77).Five water groups were identified based on characterization in the piper trilinear diagram. These include Ca-Na+K-HCO_3, Na+K-HCO_3, Na+K-HCO_3-Cl, Ca-Cl-HCO_3, and Ca-Na+K-SO_4. They reflect diverse effects of bedrock lithologies, base exchange processes, precipitation and weathering. The groundwater source is strongly to weakly acidic fresh water with the exception of water sample (WS2) showing slightly alkaline fresh water. The water samples are generally soft with low sodium content. The groundwater quality is good and satisfies the World Health Organization (WHO) guidelines and the Nigeria Standards for Drinking Water Quality (NSDWQ) for domestic, agricultural and other industrial uses requiring minor treatment.