Evaluation of the hydrochemistry and pollution levels in groundwater of Njahasang, Southeast Nigeria

This study assesses groundwater quality, chemistry, and pollution levels in Njahasang, southeastern Nigeria, by evaluating physicochemical parameters. Fifteen (15) groundwater samples were collected and analyzed using standard laboratory techniques. Physical parameters were measured using the HANNA Instrument multi-parameter probe (model HI9813). Major anions were analyzed using volumetric methods (HCO₃⁻, Cl⁻), colorimetric methods (SO₄²⁻), and ultraviolet (UV) spectrophotometry (NO₃⁻), while major cations and heavy metals were determined using an Atomic Absorption Spectrophotometer (Bulk Scientific model 210VGP). Results showed that major cations followed the order: Ca²⁺ > Mg²⁺ > Na⁺ > K⁺, anions followed HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻, and heavy metals followed Mn > Fe > Zn > Cr > Cd > Pb. The Water Quality Index (WQI) indicated that all groundwater samples were of excellent quality for domestic use. Hydrochemical facies identified Ca²⁺-Mg²⁺-HCO₃⁻ and Ca²⁺-Mg²⁺-SO₄²⁻ water types. Chloro-alkaline indices (CAI-1 and CAI-2) revealed a dominant reverse ion exchange process, as all values were positive. Cluster analysis suggested both geogenic and anthropogenic sources of ion contamination, while Gibbs plots indicated that rock-water interaction and host rock weathering were the primary processes controlling groundwater chemistry. The degree of contamination (Cd) indicated low contamination overall, except for Mn, which exhibited moderate levels based on the contamination factor (Cf). According to the Pollution Load Index (PLI), 27% of the samples showed progressive deterioration, likely due to elevated Mn concentrations from shales, while 73% exhibited no pollution. Plots, tables, and models based on major ionic constituents provide an effective visualization of groundwater quality and chemistry.