Abstract
Resistivity surveys have been utilized to delineate the sand horizons and possible water bearing zones in the shallow Quaternary deposits that mask the Benin Formation that underlies the Sombreiro-Warri Deltaic Plain at Orerokpe in the western Niger Delta. Fifteen dug wells and shallow boreholes were sampled for water quality analysis. The results show that from the surface to about 70m, there are four layers of water bearing sands that are separated in places by discontinuous clay horizons. Depth to water level ranges from 3.5m to 5.5m. Ground water flow is from northeast to southwest towards the Warri River. Ground water which is used here for domestic purposes without treatment is soft and it is shown that the most important factor contributing to groundwater chemistry is weathering of the aquifer matrix. The order of preponderance of the cations is Na+ > K+ > Ca2+> Mg2+ and HCO3 - > SO4 2-> Cl- for the anions; trends that are not only a departure from normal pristine conditions, but also basically different from those observed in nearby Warri and indicative of possible contamination. The relatively low calcium and magnesium content is identified as a potential health problem if water constitutes the main source of ingestion of these ions. The results reinforce the complex geological nature and geochemical conditions that exist in the Quaternary superficial deposits of the Niger Delta environment.
Highlights
The Niger Delta is one of the most important petroleum provinces in the world as a result of which the petroleum geology of the area has been subject of intense study
The quality of water yielded is crucial but various studies (Ejechi et al, 2007; Akpoborie et al 2000; Olobaniyi et al 2007; Abimbola et al 2002). Have indicated that these shallow aquifers are highly vulnerable to contamination from surface sources as a result of which the quality of groundwater in many cases been compromised by contaminants
The primary objective of this study is to identify and delineate at greater depth than that penetrated by dug wells, the configuration of the Quaternary sands and clays that are known to underlie the Orerokpe area as well as establish general ground water conditions
Summary
The Niger Delta is one of the most important petroleum provinces in the world as a result of which the petroleum geology of the area has been subject of intense study. The practice has been to generally lump these deposits of alternating finemedium grained sands, silts and subordinate lensoid clays together as the recent and present day deposition of sediments on the Benin Formation, Amajor (1991) These important deposits possess distinct characteristics and engineering properties (Bam, 2007), and cover more than 70 per cent of the land surface of Delta State, Nigeria, Figure 1. Have indicated that these shallow aquifers are highly vulnerable to contamination from surface sources as a result of which the quality of groundwater in many cases been compromised by contaminants Based on these considerations, the primary objective of this study is to identify and delineate at greater depth than that penetrated by dug wells, the configuration of the Quaternary sands and clays that are known to underlie the Orerokpe area as well as establish general ground water conditions. The electrical resistivity method that is selected for this study has been used successfully for many geological and ground water investigations in the Niger Delta (Atakpo and Akpoborie, 2011; EtuEfeotor, and Michalski, 1989; Atakpo et al, 2008; Okolie et al 2000.)
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