Variation of groundwater depth and cation concentrations with CBRs of residual soils: Case study of three lithologic terrains from North-central Nigeria

Twenty nine (29) water samples and 24 soil samples were collected from three lithologic terrains. The waters were subjected to Atomic Absorption Spectrophotometer (AAS). The soils were subjected to California Bearing Ratio (CBR) tests. The AAS revealed that water from gneiss/schist terrain have mean Ca2+, Na+, Mg2+ and K+ concentrations of 25.09, 13.14, 10.92 and 3.90 mg/l respectively; water from granite terrain have mean Ca2+, Na+, Mg2+ and K+ concentrations of 13.68, 6.39, 5.45 and 2.78 mg/l respectively while water from sandstone terrain have mean Ca2+, Na+, Mg2+ and K+ concentration of 7.82, 1.61, 1.41 and 2.16 mg/l respectively. The CBR tests revealed that the soils from gneiss/schist terrain have mean soaked and unsoaked CBRs of 12.37% and 13.75% respectively; soils from granite terrain have mean soaked and unsoaked CBRs of 35.25% and 65.53% respectively; while soils from sandstone terrain have mean soaked and unsoaked CBRs of 78.13% and 104.13% respectively. Results revealed that terrains of shallow groundwater depth are characterized by low CBRs and vice versa. This work has shown that the variation existing between the groundwater cation concentrations and overlying residual soil CBRs is based on the intrinsic properties of the lithology that formed the soil and that is hosting the groundwater.