Subsoil Characteristics and Hydrogeology of the Export Processing Zone, Calabar-Southeastern Nigeria

Abstract

The subsoil characterization and hydrogeological investigation of the Export Processing Zone (EPZ), Calabar Southeastern Nigeria was undertaken using geotechnical analysis of soils and water level monitoring. Geotechnical analysis of soils in the EPZ show that the grain size range from poorly graded (well sorted) to well graded (poorly sorted) soils with very little or no fines (0.1-5.30% passing 0.075mm sieve). Permeability values vary from 6.80 x10-3 cm/s to 9.43 x10-3 cm/s for the sandy clay to gravelly clay, to 7.00 x10-1cm/s to 8.70 x10-1cm/s for the coarse sand to gravelly sand. Soil consistency shows a plasticity range (7.00 – 13.00%) for the clayey soils with the predominantly sandy soil being non-plastic. The local groundwater migration in the area is towards the north easterly direction, meaning that the local flow pattern discharges towards area which has the lowest groundwater elevation. Following this, the implication is that subsurface water migration in the area will move towards and intersect the Calabar River flowing mostly in a southerly direction. This, by implication, will decrease the concentration of probable contaminants due to dispersion and other attenuation effects. Therefore, regular assessment of the subsoil characteristics and hydrogeology of the area will provide baseline data for planning in order to reduce the associated/attendant negative environmental hazards of export processing activities.