Variation of Some Hydrogeochemistry with CBR of Residual Soils from North-Central Nigeria: Impact of Underlying Lithology

Abstract

This work was done in an area lying between latitudes 9o051N and 9o361N and longitudes 6o011E and 7o001E which is underlain by Pan-African Nigerian Basement Complex gneiss/schist and granite and Campanian Bida Sandstone. A total of 18 water and 18 soil samples were collected from water wells and soil pits respectively occurring in the 3 lithologic terrains. The water samples were subjected to atomic absorption spectrophotometer to determine the concentrations of the cations - Ca2+, Na+ and Mg2+. The water samples were also tested with digital titrator to ascertain the total hardness and with EC meter to determine the electrical conductivity. The soil samples were subjected to sieve analysis to determine the soil types and to California bearing ratio (CBR) test to determine the CBR of the soil. Results of the atomic absorption spectrophotometer reveals that concentration of Ca2+, Na+ and Mg2+ in the water samples ranges from 5.2 to 45.3 mg/l, 1.0 to 22.5 mg/l and 0.2 to 23.9 mg/l respectively; results of the digital titrator reveals that the water total hardness ranges from 11.0 to 184.0 mg/l while results of the EC meter reveals that the water electrical conductivity ranges from 20.0 to 640.0μS/cm. The sieve analysis reveals that all the soil are coarse-grained while the CBR test reveals that wet CBR of soils ranges from 1.45 to 132.42%. Result of the tests show that water samples collected from gneiss/schist terrain have relatively high concentration of the cations - Ca2+, Na+ and Mg2+, total hardness and electrical conductivity while the soils collected from same (gneiss/schist) terrain have relatively low wet CBR. The reverse situations occurred in water and soil samples collected from sandstone terrain. Water and soil samples collected from granite terrain have relatively intermediate values. This work has shown that the inverse variation existing between the groundwater hydrogeochemistry and soil CBR is controlled by the mineralogy and texture of the underlying lithology that formed the soil and hosting the groundwater.