Environmental Geological Baseline Study of Obite Gas Plant, Eastern Niger Delta, Nigeria

In this study, a total of six (6) boreholes were sunk with rotary drilling equipment to depths of about 60 ft (about 18.30m) for BH1, BH2 and BH3. Boreholes 4, 5 and 6 were drilled to 13.60m, 12.60m and 12.20m, respectively. The measured static water levels fall between 4.45m, 3.75m, 0.94m, 6.30m, 6.10m and 6.20m for BH 1, BH 2, BH 3, BH 4, BH 5 and BH 6, respectively. All the boreholes are overlain by a reddish brown, fine grained, silty clay overburden of 3.00m to 4.60m in thickness. This is followed by a thinner stratum of dark brown, fine-medium grained, clayey sand in BH4 and BH5, which is absent in BH6. Another layer of silty clay underlies this formation in both the boreholes with a 0.9m thickness of clayey sand in BH4 preceding the sand and gravelly sand aquifer. There is less measure of uniformity in lithostratigraphic correlation between BH6 and the other two boreholes located within proximate vicinity. Below the overlying silty clay soil, BH6 records a rhythmic succession of loose sand and medium to very coarse, and moderately plastic, gravelly silty clay intercalations, before the aquifer (gravelly sand) is encountered. With respect to the area, the subsurface drainage pattern is multi-directional from north-east to the south-west and vice versa, with the migration being more inclined west-wards towards the location of BH3, which records the lowest depth to water table. Leachates introduced at a given point in the area will migrate as pollution plumes along these flow paths.