Geochemical assessment of water quality for irrigation in abandoned limestone quarry pit at Nkalagu area, southern Benue Trough, Nigeria

In the study, the quality of groundwater for irrigation is assessed. The following parameters were analysed using American Public Health Association standard method: pH, turbidity, electrical conductivity, total dissolved solids, Mg²⁺, SO₄²⁻, Cl⁻, HCO₃²⁻, K⁺, Na²⁺ and Ca²⁺. Important constituents that influence the water quality for irrigation are electrical conductivity which ranges from 4 to 1560 µS/cm, soluble sodium percentage which ranges from 4 to 33%, magnesium adsorption ratio (MAR) which ranges from 30 to 81, Kelly’s ratio which ranges from 0 to 0.5, sodium percentage (Na %) which ranges from 4 to 50%, sodium adsorption ratio which ranges from 0 to 0.6, residual sodium carbonate (RSC) which ranges from 1.5 to 3.5, permeability index which ranges from 157 to 675% and total hardness (TH) which ranges from 102 to 614 mg/L in Nkalagu water. The above estimated parameter values satisfy the various permissible standard values for irrigation except MAR, TH, RSC that are slightly above the various permissible standard values. The hydrogeochemical facies analysis plotted in Piper diagram reveals that 53.85% of the samples are predominantly (Cl⁻–SO₄²⁻) facies, 15.38% are (SO₄²⁻–Cl⁻ and SO₄²⁻–Cl⁻–HCO₃⁻) facies, while 7.69% are (Mg²⁺–SO₄²⁻–Cl⁻–HCO₃⁻ and Cl⁻–SO₄²⁻–HCO₃⁻) facies. The water type is Ca–Cl₂ with much considerable permanent hardness. Although some samples satisfied the various permissible standard values for irrigation, treatment is, however, very strongly recommended to improve the quality and make it more suitable for irrigation.