OBEN GAS DEVELOPMENT PROJECT

Chapter Three Description of Environment
Table 3.3b: Physicochemical Characteristics of Soil in the Oben Field Area (Wet Season)
S/N PARAMETERS SS1 SS2 SS3 SS4 SS5 SS6 SS7 SS8 RANGE
1 Particle Size Analysis
% Sand
77.3 81.32 80.3 79.4 78.4 80.3 81.2 79.3 77.3 – 81.32
% Silt
1.81 2.13 2.23 2.21 1.93 2.10 1.90 2.10 1.81 – 2.23
% Clay
3.94 4.24 13.94 13.11 14.10 13.10 12.10 14.11 3.94 – 14.11
2 pH 4.9 5.0 5.1 6.0 6.1 6.3 6.2 6.4 4.9 – 6.4
3 Electrical Conductivity
(u s /cm)
150.0 165.0 161.0 155.1 161.0 159.1 161.0 162.1 150 – 165.0
4 Organic matter (%) 2.98 3.81 3.95 4.12 4.78 4.10 5.10 5.98 2.98 – 5.98
5 Total Nitrogen (%) 0.43 0.90 0.91 0.81 0.99 1.58 1.67 1.71 0.43 – 1.71
6 Available Phosphorus
(mg/Kg)
21.23 38.1 40.2 39.3 90.5 61.3 62.3 48.4 21.23 – 90.5
7 Exchangeable Cations
(cmol/kg)
Ca
0.25 0.28 0.22 0.36 0.29 0.40 0.32 0.34 0.25 – 0.34
Mg
0.45 0.61 0.75 0.66 0.65 0.66 0.80 0.70 0.45 – 0.80
Na
0.50 0.55 0.70 0.50 0.49 0.55 0.55 0.54 0.49 – 0.50
K
0.40 0.40 0.41 0.41 0.40 0.24 0.45 0.35 0.24 – 0.45
8 Cation Exchange
Capacity
1.21 1.87 1.96 1.39 1.41 1.48 1.39 1.42 1.21 – 1.96
The calcium values ranged from 0.12 to 0.28 cmol/Kg with an average of 0.16-cmol/Kg soils in the dry
season and 0.25 to 0.34 cmol/Kg and a mean value of 0.29 cmol/Kg in the rainy season. The mean
magnesium and potassium values are 0.61 and 0.16 cmol/Kg soils respectively in the dry season
and0.65 and 0.40 cmol/Kg in the rainy season respectively. The high rainfall from April to October and
high soil porosity encourages leaching of soil nutrients into subsoil outside the reach of most plants. As
with the exchangeable cations, the cation exchange capacity (CEC) values are low. The values ranged
from 1.05 - 1.87-cmol/Kg soil with an average of 1.42-coml./Kg soil in the dry season and1.01 - 1.76cmol/Kg
soil with an average of 1.52 cmol/Kg soil in the dry season (Table 3.3a and 3.3b).
The heavy metal concentrations of the soils in Oben Field are shown in during the dry and rainy
seasons are shown in Tables 3.4a and 3.4b respectively. The values are low except for iron whose
concentration ranged between 115 and 340 mg/kg in the dry season and 163.4 and 493.7mg/Kg in the
rainy season . Most of the heavy metal values are below limits that can be of environmental concern. In
a decreasing order, the concentration of the heavy metal are as follow: Fe > Zn > Mn > Cr > Cd > Pb >
Ni > V > Cu. The total hydrocarbon (THC) values are low and below the 50 mg/kg found in soils with
luxuriant growth of plants. The values ranged from 2.40 to 25.61 mg/kg with an average of 9.82 mg/kg.
The low THC values may be due to lack of oil spill incidence in the area.
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