Acid mine drainage is by far the most significant long term groundwater quality
impact associated with both opencast and underground coal mining, in both a local
and international context. The modern day geohydrologist has access to numerous
tools, which can be used to determine important decant issues â issues ranging from
when decanting will begin to occur, and the volumes of water that are expected to
decant.
The continuous development and improvement of numerical groundwater flow
models is steadily leading to an increasing dependence on them. The main aim of
the thesis was to determine whether there exists any correlation between modern
day numerical groundwater flow models and analytical calculations, and the
presentation of a toolbox of tools that may be used for decant related issues. The
following conclusions were drawn after numerous numerical and analytical scenarios
and statistical correlations were performed:
⢠Given the amount of uncertainty regarding aquifer heterogeneity, there do
exist a good correlation between the numerical and analytical groundwater
decant volume estimations,
⢠An increase in the effective porosity of the backfilled opencast pits cause an
increase in the time-to-decant, as more water is required to fill the pits to their
decant elevations,
⢠An increase in the effective aquifer recharge cause an increase in the decant
volumes and a decrease in the time-to-decant, because more water is
available to fill the pits to their decant elevations,
⢠The effective aquifer recharge is a very sensitive parameter (more so than
specific yield, storage coefficient, and transmissivity), as significant decreases
in the time-to-decant were simulated with an increase in the aquifer recharge,
as were significant increases in decant volumes simulated with an increase in
recharge,
⢠The volumes of groundwater decant are more sensitive to variations in the
transmissivity of the surrounding aquifer/s compared to the transmissivity of
the backfilled opencast pits,
⢠During the numerous flow model scenarios it was found that the groundwater
contribution to pit water is far less compared to the recharge component.
The above conclusions prove that there are still applications for analytical
calculations in modern day geohydrology, despite the continuous development of
numerical groundwater flow models.
Based on experience in similar coal mining operations within the Mpumalanga coal
fields, the results of both the analytical decant volume and time-to-decant
estimations correspond well with actual figures. One must however understand and
master the various equations and keep in mind that an aquifer is a highly
heterogeneous system. The results of both numerical groundwater flow model
simulations and analytical calculations are only as good as the understanding of the
geohydrological environment and the data they are based on.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-11112011-091847 |
| Date | 11 November 2011 |
| Creators | du Plessis, Johannes Lodewiekus |
| Contributors | Dr I Dennis |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-11112011-091847/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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