Site characterisation for LNAPLs investigation using electrical resistivity tomography (ERT) survey
| dc.contributor.advisor | Vermeulen, Danie | |
| dc.contributor.advisor | Lorentz, Simon | |
| dc.contributor.author | Ngeleka, John Kalala | |
| dc.date.accessioned | 2018-01-12T09:01:56Z | |
| dc.date.available | 2018-01-12T09:01:56Z | |
| dc.date.issued | 2009-11 | |
| dc.description.sponsorship | This thesis is part of the project that the South African government and research institutions had initiated to study the fate and the transport of the LNAPLs contaminant in groundwater. The aim of the dissertation is to characterize the geology and hydrogeology of the Joint Fuel Depot site in East London, as well as to characterize the state of groundwater which is exposed to LNAPLs contamination from the tank’s leakage. This characterization has lead to the drawing of a geological and hydrogeological conceptual model of the site. Site characterization has been initiated as the first step of the investigation to provide detailed information on the geological and hydrogeological conditions of the site. Such information is important as it leads to a better understanding of the position and flow of LNAPLs in the sub-surface and how the groundwater is affected. The electrical resistivity tomography (ERT) was selected as one of the techniques to delineate the geological units, to locate the aquifers as well as weathered and fractured zones which are considered as preferential pathways of groundwater and contaminants. The literature review and site description had a permit to acquire relevant information on the previous use of the ERT techniques in LNAPLs site characterization and on the local geological and hydrogeological setting. ERT techniques have proved to be applicable and appropriate for this investigation. ERT is a 2-D electrical resistivity technique which uses an automatic multielectrode instrument to inject a current into the ground through two electrodes, and which measures the voltage drop at two other electrodes. The injection of a current and the measurement of the voltage drop are sequentially repeated along a line of several electrodes to produce a 2-D resistivity distribution of the subsurface. Like any other geophysical methods, the ERT results need to be complemented by other field testing results to permit an integrated interpretation which leads to the complete characterization of the LNAPLs site. The field testing includes soil testing, groundwater testing, borehole logs and groundwater levels. The soil testing provided the initial soil water content, soil particle distribution and the spatial distribution of volatile organic carbons on the site. Groundwater testing evaluates the presence of petroleum hydrocarbons in the saturated zones. Borehole logs gave the nature and thickness of geological units and water level data allowed to determine the direction of the groundwater on the site. The field testing results were very useful in ERT interpretation. They have been used to compare to the contrasts revealed in the resistivity model sections provided by the ERT surveys. This integrated interpretation has lead to establish, firstly, that the Joint Fuel Depot site is underlain by four major geological units including the sand, clayey sand, clay and dolerite sill; and secondly, that there is evidence of LNPALs contaminant on the surface of the groundwater. From the integrated interpretation of the results, it could be concluded that the ERT survey has proved to be applicable in the LNAPLs site characterization. It is recommended that the ERT survey be used for threedimensional resistivity distributions for a more accurate delineation of LNAPLs plumes and that a time-lapse survey be considered to monitor the changes and progress of LNAPLs contaminant in the subsurface. | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/7590 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Hydrogeology -- South Africa -- East London | en_ZA |
| dc.subject | Tomography | en_ZA |
| dc.subject | Groundwater -- Pollution | en_ZA |
| dc.subject | Nonaqueous phase liquids | en_ZA |
| dc.subject | Dissertation (M.Sc. (Institute for Groundwater Studies))--University of the Free State, 2009 | en_ZA |
| dc.title | Site characterisation for LNAPLs investigation using electrical resistivity tomography (ERT) survey | en_ZA |
| dc.type | Dissertation | en_ZA |