The rehabilitation and restoration of degraded landscapes adjacent to gold tailings disposal facilities (TDFs) that have suffered loss of efficiency through anthropogenic forces has become a primary concern to environmental sciences and management in recent decades. Due to the lack of environmental legislation and enforcement thereof, minimal surface rehabilitation took place on the Mine Waste Solutions (MWS) No. 5 TDF prior to 1992, a commonplace occurrence in South Africa at the time.
In 2000, MWS intervened and committed to the rehabilitation of the entire site with profits generated by the reprocessing (extraction of residual gold and uranium) of certain TDFs. However, the adjacent grazing land north of the MWS No. 5 TDF had already been subjected to pollution from the TDF which resulted in a pollution plume on the land.
Although it has been inactive since April 2011, the pollution plume can be seen from the north-eastern corner of MWS No. 5 TDF, with a north-eastern/south-western direction on the farm Stilfontein. During dry periods, significant amounts of sulphate salts accumulate on the soil surface on the farm Stilfontein over a distance of at least 3.5 km from the TDF. The presence of sulphate salts in association with gold TDFs is highly common but not particularly common, in the chert-poor dolomites of the Oaktree Formation itself, in which the presence of sulphate salts is a rarity.
The primary concern of this study was to determine both the quantitative and extent of the pollution observed on the farm Stilfontein over a period of 30 months via monthly monitoring of the different soil geochemical assessments across twelve fixed points, and quarterly interval assessments of three transect lines. In addition, the study was also concerned with the identification of potential linear structure anomalies associated with the pollution plume and weathered zones (fractures, joints and cavities) in the Oaktree Formation dolomites. These zones may be associated with, or may result in, the pollution extending over the area despite a topography as well as geological dip and strike that is adverse.
These features and weathered zones create pathways for groundwater to flow and it was anticipated that, if present, these anomalies and weathered zones may be primary contributing factors to the pollution plume forming in a north-easterly direction and extending over the farm Stilfontein. The MWS No. 5 TDF has a hydraulic pressure head of approximately 40 m; the elevations of the north-eastern corner of the TDF and fixed point (FP) 8 (the farthest FP from the TDF) are 1368 m and 1360 m respectively, falling in close range of each other. It is anticipated that as the TDF material dries, the phreatic water level inside the TDF will lower; causing the pressure exerted by the hydraulic head of the TDF to lower over time, which will eventually end the pollution process on the soil.
This study discusses the results of a holistic approach towards the evaluation of soil, vegetation and water pollution by utilizing soil quality parameters and indicators, geohydrology, geophysical surveys, Landscape Function Analysis (LFA) and other means of vegetation assessments.
Salt accumulation on the soil surface was common in specific areas from 2010 – 2012. X ray diffraction (XRD) analyses confirmed that the salts originated from the No. 5 TDF due to the similarity in mineralogy.
The pH values from the start of the 30-month monitoring period remained neutral to slightly alkaline due to the neutralising effect of the dolomitic bedrock. The electrical conductivity (EC) values of the soil decreased significantly from 2010 to 2014; during dry seasons since 2012, no sulphate salts accumulated on the soil surface. Joints, fractures and cavities were found within the bedrock dolomites which created pathways for the polluted TDF water and groundwater to flow towards the study area.
It was also established that there were no adverse effects on the natural vegetation, other than encroachment by Seriphium plumosum which affected the grazing quality (overgrazed sites) of the area. It was therefore concluded that after the TDF became dormant in April 2011, the pollution plume in this area is decreasing in magnitude and severity due the lowering of the phreatic water level inside the TDF to significantly lower levels. Consequently, the decrease of the hydraulic pressure head of the TDF as well as rainwater infiltration and high percolation due to the presence of fractures, joints and cavities in the dolomites resulted in the leaching of the sulphate salts to a significant extent. It was also concluded that while there were no apparent adverse effects of the pollution on the functionality of the land, additional monitoring and maintenance would be required for at least the next five years in order to ensure the continuance of current conditions. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/14914 |
| Date | January 2015 |
| Creators | Daniell, Angelique |
| Source Sets | North-West University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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