Evaluation and characterization of groundwater of the Maastrichtian Lafia formation, Central Benue trough, Nigeria

Abstract

Hydrochemical assessment of groundwater in the Lafia formation, Central Benue trough, Nigeria was carried out with the aim of determining its quality for domestic and irrigation purposes. Thirty groundwater samples from boreholes and hand-dug wells were analyzed using atomic spectrometry and titrimetric methods. The water quality index (WQI) was evaluated from physicochemical parameters and used in assessing the groundwater quality for drinking, while the electrical conductivity (EC), percentage sodium (%Na), sodium absorption ratio (SAR) and magnesium hardness (MH) were evaluated to assess its suitability for irrigation. The physico-chemical parameters in order of dominance are $\hbox {HCO}_{3}^{-} >\hbox {NO}_{3}^{-}>$ Cl- > $\hbox {PO}_{3}^{-} >\hbox {SO}_{4}^{2-}$ for the anions and $\hbox {Fe}^{3+}>\hbox {Na}^{+}>\hbox {Ca}^{2+}>\hbox {Mg}^{2+}>\hbox {Pb}^{2+} >\hbox {K}^{+}$ for the cations. The pH indicates acidic to weakly alkaline water (5.1–7.3); EC ranges from 110 to 1396 $\upmu$S/cm, while the total dissolved solids range between 136.9 and 3.4 mg/l, based on which it is classified as freshwater. WQI showed that only 40% of the groundwater samples are suitable while 60% are unsuitable for drinking and will therefore require treatment. Three water facies: $\hbox {Ca}^{2+} + \hbox {Mg}^{2+}, \hbox {Ca}^{2+} + \hbox {Na}^{+} + \hbox {K}^{+}$ and $\hbox {HCO}_{3}^{-}$ characterized the area indicating the groundwater-quality situation. Based on EC classification, 33.33% of the water samples are considered excellent, 60% as good, 6.67% as permissible while on the basis of %Na, only 13.34% are unsuitable for irrigation. SAR of 96.67 and 3.33% of the groundwater samples indicate excellent and doubtful waters, respectively. 93.4% of groundwater samples has MH < 50 and are considered suitable for irrigation.