Assessment of Groundwater Potential in Parts of the Coastal Niger Delta, Nigeria: Implications for Well Design

The location, design, drilling and completion of wells for potable groundwater abstraction require exploration and mapping of groundwater potential zones within the geologic framework of any region. In this study, field data acquisition involved seven vertical electrical sounding and three horizontal resistivity profiling (HRP) carried out. Field data were interpreted using IPI2win 1-D software while subsurface lithologic layering and correlation was realized in rockworks v 22. Modelled true geolectric sections after curve matching revealed the study area to be underlain predominantly by clayey lithologic units followed by coarse grained sands with silty sands and fine sands in minor fraction. Total investigation depth range between 314.0m and 510.0m and fresh water was found to occur at a depth of 168m in VES L2, 430m in VES L3 and 154m in VES L6 locations. Iron water was found in some coarse sands at a depth interval of 129 m to 314 m at VES L1 while fresh water in coarse sands underlain by iron water saturated fine sands occurs at a depth interval of 73.20 m to 206 m at VES L2. At VES L3, fresh water saturated coarse sands were found at a depth interval of 131 m to 430m. Boreholes should be drilled to 430m and screened from 131m to 430m at L3. At VES L4, fine sands overlying coarse grained sands were saturated with iron water from 50.20 m to 422m. At VES L6, fresh water saturated coarse grained sandy aquifer was found from 114 m to 154m. Although VES L2, L3 and L6 provides the most suitable prospective locations for fresh water in the area at depths of 168m for L2, 430m for L3 and 154m for L6, lithologic modelling revealed that both coarse sands and fine sands are either juxtaposed or interfingered at the shallow, intermediate and deeper depths, hence, there is strong potential for iron water and fresh water inter-mixing during pumping. All twenty proposed boreholes are recommended not to be pumped at rates exceeding 3,500 l/min. Boreholes should be 450m apart to prevent well interferences and pumping schedule of 10 to 14 boreholes daily will greatly reduce stresses on the well field as well as potential risk from saline intrusion. Three saline water encroachment monitoring boreholes should be sited at 1.5km from L1 and L2 and 2.4km from L7 respectively at the East, West and Southern sections of the plant area.