Geo- Electric Characterization Of Recent Hydrocarbon Contaminated Soil And Groundwater In Parts Of Ogale Community, Eleme Local Government Area Of Rivers State Nigeria.

Abstract

Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) were jointly carried out to characterize petroleum hydrocarbon impacted site, in parts of Ogale Community, Eleme Local Government Area of Rivers State, using ABEM Terrameter SAS 1000. The objective is to delineate the lateral and depth extensions of the hydrocarbon contaminated soil and groundwater. The VES and ERT were taken parallel to NNPC oil pipeline. The interpreted geo electric sections from the VES result revealed five geo-electric layers. The first geo-electric layer has resistivity value of 59.80ΩM and a thickness of 1.93.m. This layer is interpreted as topsoil. The second layer which has a resistivity value of 143.32ΩM with a thickness of 2,92M was interpreted as lateritic sand. The third geo-electric layer has a resistivity value of 480.4ΩM and a thickness of 11,22M and this layer is interpreted as moderately hydrocarbon contaminated fine sand. The fourth geo-electric layer has a resistivity value of 793ΩM with a thickness of 32.7M and this layer is interpreted as hydrocarbon contaminated aquifer. The fifth geo-electric layer has a resistivity value of 319 ΩM, both depth and thickness are unknown. From the Tomogram results three resistivity zones were identified, the deep blue zone which has a resistivity value of 33.4ΩM with a depth of 0.89m and this is interpreted as topsoil. The second zone is the green –yellow resistivity zone which has a resistivity value of 694 ΩM with depth ranging from 0.98m to 14m and this is interpreted as moderately hydrocarbon contaminated fine sand. The third resistivity zone is the pick –purple zone. This zone has a resistivity value of 1328ΩM with depth ranging from 3.0m to 14m. The pink purple zone is interpreted as hydrocarbon contaminated aquifer. The vulnerability of the aquifer to hydrocarbon contamination is due to unconsolidated sand, high porosity, permeability, sands are poorly sorted and coarse grained, heavy rain fall, aquifer nearness to hydrocarbon spill site and ground surface. Soil degradation due to hydrocarbon contamination may alter the bulk density of the impacted soil and this may affect the compressibility and hydrogeology of the soil, infiltration rate and direction of groundwater flow which may alter groundwater recharge from precipitation in the investigated site