Hydrogeochemical evolution and groundwater quality assessment using chemical systematics, statistical techniques, and pollution index of groundwater (PIG): a case study

Abstract

Herein, we investigate the hydrogeochemical processes influencing the chemistry and suitability of groundwater for drinking in Mubi south area, north-eastern Nigeria based on physicochemical results of water samples collected from 30 boreholes in the area. The cations and anions distribution in the samples are in the order Mg2+ > K+ > Na+ and HCO3− > NO3− > Cl− > SO42− > CO32− respectively. The low turbidity (0.02–4.86 NTU) and neutral–mildly alkaline nature (pH = 6.65–8.70) of the groundwater indicate high clarity, low level of cloudiness, high CO2 abundance and dissolve ions in form of HCO3−. Hydrogeochemical (e.g., Piper, Durov, bi-variant and scatter plots) and statistical (PCA and HCA) evidences highlight the biogeochemical hydrolysis (i.e. silicate weathering) of silicate minerals (such as K-feldspars, pyroxenes, amphiboles) as the major process controlling the groundwater chemistry. The dominance of Ca2+–Mg2+–HCO3− water type, coupled with the strong positive correlation between EC and K+ (r = 0.75), and the strong positive loading of Ca+ (0.74) are robust evidences for the silicate weathering process. However, the elevated Cl− concentrations (15–206 mg/l), and the insignificant variation of Na+/Cl− ratio with increasing EC as well as the high positive loadings of EC and TDS imply other secondary processes (e.g., evaporate salts and anthropogenic pollution) were also involved in the hydrogeochemical evolution. The pollution index of groundwater (PIG = 0.27–0.737) fall below the insignificant pollution state of less than 1, diagnostic of good water quality for drinking purpose and sustainability of public health.