Abstract
The JES field, an onshore field in the Jisike – Izombe area of southeastern Nigeria had a number of oil-producing wells before it was abandoned over a decade ago. By means of soil/sediment samples retrieved from three strategically located boreholes around the field, the subsurface units were delineated and the physical characteristics of the vadose zone were determined in order to predict the groundwater pollution potential of the upper aquifer system in the area. Ground conditions were found to be approximately 1metre (3.043ft) of loamy top soil overlying about 1.2metres (3.65ft) of clayey laterite which overlies 19.4 – 24.6metres i.e (60ft – 75ft) of reddish-brown silty sand, beneath which is medium – coarse grained white sand which constitutes the aquifer system with estimated hydraulic conductivity in the range 1 x 10 -1 to 169 x 10 -1 mm/sec. Flow analysis of groundwater indicates a southwesterly flow with the River Niger as possible discharge zone. The high leaching potentials and high transmissive properties of the sediments below the clayey laterite suggests a vulnerability of the aquifer to pollution through vertical infiltration. However, borehole water quality parameters for the area show that groundwater quality is not in anyway compromised when compared to the WHO limits. Rather, it is argued that the groundwater is naturally well protected by the upper part of the vadose zone where the clayey lateritic soil with iron oxide cementation of soil particles provides an appreciable degree of barrier to downward movement of contaminants. Because of the clayey behavour of the near-surface soils and their affinity for the retention of contaminants, it is concluded that the area is not a locus of groundwater pollution. © JASEM
Highlights
Petroleum activity has been on for many years over a vast area in the Niger Delta region of Nigeria covering some 6400km2 on-shore and 76,000km-2 off-shore
The lateral continuity of this unit is broken in BH1 and BH2 by reddish brown medium to coarse-grained silty sand interspersed with gravel
The result of the analysis indicates a southwesterly flow of groundwater with the River Niger as a possible discharge zone
Summary
Petroleum activity (exploration and exploitation) has been on for many years over a vast area in the Niger Delta region of Nigeria covering some 6400km on-shore and 76,000km-2 off-shore. The JES field located in the Jisike – Izombe area of southeastern Nigeria is one of the on-shore oil fields within an estimated total land area of about 3.95km2 It was discovered in 1975 and is adjacent to and east of Izombe field. It is imperative to carry out an Environmental Impact Assessment (EIA) as a sine-qua-non of a field development plan (FDP) prior to the commencement of the project Where this had not been done, prediction of impacts of petroleum activity would be based on a postimpact assessment (PIA) and environmental evaluation report (EER) relying essentially on control samples, since baseline data would not be available. It is often necessary to characterize the geomaterials above the aquifer (vadose zone) because of the need for groundwater protection against pollution
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