Geochemical Characterization of Sediment and Ground Water Contamination in Addis Ababa City from Petroleum Stations
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Date
2015-06-06
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Addis Ababa University
Abstract
Addis Ababa is located on the shoulder of the Western Main Ethiopian Rift Escarpment in which the city is surrounded by mountain ridges from north and northwest and gentle slope to south and southeast part. The general surface and groundwater movement direction is dominated by north-south and east-west flow. Hydrogeologically the area characterized by fracture porosity and interstitial porosity and lithostratigraphic units from bottom to top includes Alaji basalts, Entoto silicics, Addis Ababa basalts, Nazareth group, and Bofa basalts associated. The main focus of the study is geochemical characterization of groundwater contamination in Addis Ababa mainly related to organic contaminants from petroleum station. Physico-chemical parameters: such as EC, TDS and PH, measured in-situ and from secondary sources; redox sensitive compounds and major ions analysis from secondary data; laboratory analysis of COD and Organic Carbon from ground water samples taken in the field were used to characterize the chemistry and possible contamination of groundwater. These secondary groundwater quality parameters were obtained from two different sources: from Addis Ababa Water and Sewerage Authority (AAWSA) and Addis Ababa water work design and supervision. Each parameter has been determined in order to assess the contaminant distribution in the study area. The values of the parameters have been evaluated with respect to the maximum acceptable standard level of WHO (World Health Organization) for drinking and groundwater. The result of physio-chemical analysis (TDS, EC H, redos-sensitive compounds) from groundwater wells reveals that the source of the organic contaminants in the study area is difficult to identify while physical evidence from gas stations and garages suggests that organic compounds are entering surface and subsurface environment. Finally for effective remediation program this work proposes in-situ capping for sediment and air sparging for groundwater.
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Addis Ababa, Physio-Chemical, Organic Contaminant, Redox Condition, Groundwater, Cod