|
Three wells were sunk with a hand-operated light cable percussion rig to the maximum depth of 15.00 to 21.00 m. The static water levels recorded after drilling for each well were 8.00 m for borehole 1 (BH 1), 4.40 m for BH 2, and 5.00 m for BH 3. The soil stratigraphy reveals a uniform correlation in the three boreholes of medium to very coarse grained sand and gravelly sand. The lower layers are coarser, so that there appears to be a downward coarseness of the grains. There is also a downward decrease in the shade of brownish color. In BH 1, there is an upper stratum of dark brown, mediumgrained, friable sand to a depth of about 9.00 m. This is underlain by light brown, very coarse-grained, gravelly sand. BH 2 and BH 3 display similar profiles of overlying dark brown, medium-grained, friable sands of about 3.0 m in thickness. This is followed by light brown, coarse-grained sands to depths of about 15.00 m. Light brown, very coarse grained, gravelly sands extend from this depth to the maximum drilled depth of 21.00 m. The results also reveal that the soil is non-plastic and fall within the soil classification group of SP under the Unified Soil Classification System. Permeability tests of the samples are moderately high values as expected for the sandy soils and range from 7.83 x 10-1 cm/s to 8.92 x 10-1 cm/s. The hydraulic gradient between BH 1 and BH 3 is about 6% or 1 m in 16 m (1:16), while that between BH 1 and BH 2 is about 7% or 1 m in 14 m (1:14). Since the hydraulic gradient between BH 1 and BH 2 is slightly higher, more rapid effluent discharge is expected towards BH 1. This may explain the higher concentration of crude oil contamination of the groundwater, particularly within the region of the waste pit. |
