On the use of electrical resistivity methods in monitoring infiltration of salt fluxes in dry coal ash dumps in Mpumalanga, South Africa

G Steyl,I Muchingami,J Nel,Y Xu,K Reynolds

doi:10.4314/wsa.v39i4.7

G Steyl, I Muchingami + Show 3 more

Open Access

https://doi.org/10.4314/wsa.v39i4.7

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Journal: Water SA	Publication Date: Jul 10, 2013
Citations: 2	License type: cc-by

Affiliation: University of the Western Cape

Abstract

One of the principal environmental concerns relating to coal combustion waste disposal is the potential for groundwater contamination from salt fluxes and trace elements that may be leached into the underlying groundwater system. Since changes in moisture and salt concentrations usually provide contrasts in electrical properties against the host media, electrical resistivity methods can be used to monitor ingression of solute plumes as well as to detect any preferential flow paths within the ash medium. In this study, 2D electrical resistivity tomography was used to monitor brine (10% NaCl) water ingression through the unsaturated zone of a dry coal ash dump at a power station, Mpumalanga, South Africa. This was after the initial laboratory determination of the relation between electrical resistivity and moisture/salt content for the ash dump. The results showed that infiltration plume progression was more pronounced in the vertical direction, suggesting that moisture movement is mainly due to gravitational pull. There was no evidence of preferential flow within the ash medium, although the different infiltration rates for different sites suggested different permeability within the unsaturated zone.

Highlights

Despite environmental concern, coal-fuelled thermal power stations remain the main sources of electricity generation in most developing countries
Changes in resistivity were correlated to changes in moisture content during moisture and salt leachate ingression for a coal ash medium, and the relationship was successfully used to evaluate the conductivity of fluid through the ash dump
The high cementation factor obtained for the ash medium is generally associated with a medium with pore spaces that are less well connected (Tiab and Donaldson, 1996)

Summary

Introduction

Coal-fuelled thermal power stations remain the main sources of electricity generation in most developing countries. More than 90% of South Africa’s electricity is generated from the combustion of coal (Kruger and Krueger, 2005). Large quantities of solid residues (ash) remain after the combustion of coal during the electricity generation process. These large volumes of ash are disposed of in holding ponds or ash heaps, which are often referred to as ash dumps. There is a need to implement a close monitoring mechanism for the environmental impact assessment of the dangers associated with such ash dumps. In order to implement an efficient monitoring scheme, a thorough knowledge of the migration of solute fluxes within the ash dump is required

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