Quantification of the Impact of Irrigating with Coalmine Waters on the Underlying Aquifers
It is predicted that vast volumes of impacted mine water will be produced by mining activities in the Mpumalanga coalfields of South Africa. The potential environmental impact of this excess water is of great concern in a water-scarce country like South Africa. Research over a period of more than 10 years has shown that this water can be used successfully for the irrigation of a range of crops (Annandale et al. 2002). There is however continuing concern from the local regulators regarding the long-term impact that large scale mine water irrigation may have on groundwater quality and quantity. Detailed research has been undertaken over the last 3 years to supplement the groundwater monitoring program at five different pilot sites, on both virgin soils (greenfields) and in coal mining spoils. These sites range from sandy soils to very clayey soils. The research has included soil moisture measurements, collection of in situ soil moisture over time, long-term laboratory studies of the leaching and attenuation properties of different soils and the impact of irrigation on acid rock drainage processes, and in depth determination of the hydraulic properties of the subsurface at each of these sites, including falling head tests, pumping tests and point dilution tests.
This has been supported by geochemical modelling of these processes to quantify the impacts. The results indicate that many of the soils have considerable attenuation capacities and that in the period of irrigation, a large proportion of the salts have been contained in the upper portions of the unsaturated zones below each irrigation pivot. The volumes and quality of water leaching through to the aquifers have been quantified at each site. From this mixing ratios have been calculated in order to determine the effect of the irrigation water on the underlying aquifers.
KeywordsCoal mining irrigation gypsum-saturated waters attenuation capabilities
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Funding from Water Research Commission and Coaltech 2020.
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