Hydrogeochemical Investigation of Surface Water and Groundwater Resources in Nnewi and Environs of Anambra Basin, Nigeria

Abstract

The study area falls within the Anambra Basin in south eastern Nigeria. The lithostratigraphic units within the study area are Oligocene – Miocene Ogwashi-Asaba Formation and the Eocene Ameki Formation. This study investigates the hydrogeochemical analyses of the surface water and the groundwater discharge from the prolific Nanka sands reservoir. A total of twenty-four water samples were obtained from both groundwater and surface water sources from different locations within the study area and were analysed for their physico-chemical characteristics with the aim of assessing their quality and usability.  Results of some physico-chemical parameters show average values of 4.85p^H, 18.18mg/l TDS, 6.47mg/l Ca²⁺, 14.92mg/l Na⁺, 8.46mg/l K⁺, 0.67mg/l Mg²⁺, 0.46mg/l HCO₃^-, 12.27mg/l Cl^-, 0.50mg/l Fe²⁺, 1.87mg/l NO₃^- and  26.33µs/cm conductivity. The Total Hardness and Sodium Absorption Ratio are respectively 17.33mg/l and 1.82. The Total Hardness, Hydrogen bicarbonate, Calcium and conductivity are higher in the surface waters than in groundwater while Nitrate and Magnesium are comparatively higher in groundwater than in surface waters. Statistical analysis, using the product moment coefficient of correlation, indicates positive correlation between the following pairs of parameters: Total Hardness (TH) and TDS (r = 0.87); TDS and Ec (r = 0.97); Ca²⁺ and HCO₃^- (r = 0.31); Ca²⁺ and Mg²⁺ (r = 0.58). Negative correlation was obtained between p^H and Cl^- (r = -0.04) while very weak correlations were observed between p^H and TH (r = 0.18) and Na⁺ and K⁺ (r = 0.22). Seven water groups were identified based on characterization in the piper trilinear diagram. These include Na-SO₄, Ca-SO₄, Ca-Cl-SO₄, Na-Cl, Ca-Na-SO₄, Na-Mg-SO₄ and Na-Cl-SO₄. They reflect effect of different bedrock lithologies, base exchange processes, precipitation and weathering. In general, both water sources are acidic fresh water. The water samples are generally soft with low sodium content. The Sodium Absorption Ratio (SAR) and other related parameters such as p^H, NO₃^-, SO₄^2-, Cl^-, HCO₃^-, Ca²⁺, Mg²⁺, K⁺, Ec, TH and TDS falling within the permissible limits for potable water. The sources are generally suitable for both domestic and agricultural uses requiring minor treatments.