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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 Naand 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. @JASEM

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A water table head distribution map of the shallow Benin Formation aquifer in the Effurun-Warri area has been drawn from dug well data and used to define groundwater gradients as well as identify directions of groundwater movement in this densely populated urban setting. Water samples from forty dug wells were also screened for the presence of lead and cadmium and results showed a variation in concentration from not detectable to 0.04mg/l for each metal. Iso-concentration contours for lead in groundwater suggest that enrichment may be from two sources: wastes from the refinery and petrochemical industrial complex on the northwestern edge of the city and secondly from leachates associated with the many unregulated waste dumpsites. Lead appears to be constrained from spreading eastwards from the industrial complex area by the south and westwards trending groundwater gradient. The city wide prevalence of elevated levels of cadmium is also probably due to leachates from unregulated dumpsites as well as the mixing of groundwater as suggested by existing gradients. Potential implications of the findings for public health, local and regional water quality monitoring are discussed.

Groundwater conditions and hydrogeochemistry in the Sombreiro-Warri Deltaic Plain deposit at the Agbarho area were described with the aid of data obtained from dug wells. Ten dug wells and two surface water locations were sampled for water quality analysis. Regional groundwater flow is from the northeast to southwest direction with local distortion resulting from sustained groundwater withdrawal in more populated areas of the town. pH in surface water range was from 4.9 to 5.4 and that of groundwater from 3.8 to 5.9. TDS in groundwater and surface water ranges were from 39.6 to 123 mg/L and 9 to 25.6 mg/L, respectively. Two hydrochemical facies, magnesium chloride and sodium chloride facies were defined in this study. The order of abundance of cations are Mg>Na+K>Ca, Na+K>Mg>Ca and Na+K>Ca>Mg and for anions is Cl>HCO3>SO4. This study indicates that the groundwater chemistry is controlled largely by precipitation. Water qualities from the dug wells and surface water are well within the SON permitted levels except faecal coliform occurring at minimal level in two wells and one of the locations on the river.