Augmenting the Matla Sustainable Development Programme during Mining Activities and after Mine Closure

Author: Kruth, Louis
Supervisor: Professor Pieter Steyn
Date: March 2005

The “sustainable development” during the past decade has become an essential subject matter at Matla Coal Ltd. The goal of sustainability refers to the resource base itself and has also been used to refer to the livelihoods and benefits that are based on ecosystem goods, as well as services derived from the resource base.

Matla Coal Ltd has conceded to the basic premise that organizations need to adjust their operating and management practices to meet and align with community expectations. The aforementioned concept of sustainable development applies directly to Matla Coal Ltd operating practices and principles.

Surface soil erosion, as well as subsurface soil erosion projects, must be established during the mine’s life to protect the environment from long-term soil erosion. Polluted mine water, which will decant after mine closure, is one of the most common environmental disasters.

Only 50% of the in situ coal reserve does get mined, due to the mining methods used. This results in pillars being left behind for long-term surface protection, as well as work force protection. The concept of leaving pillars behind for the long-term protection of surface structures is not deemed viable as a means of ensuring that the Matla mine does not collapse in the long-term after closure. Unstable pillars will however create unstable surface structures, which will be extremely dangerous for both the community and environment. Future mining methods must therefore aim towards total coal extraction. Leaving pillars behind will adversely affect and impact the environmental restructuring programme.

The cost of addressing the environmental eruptions caused by uncontrolled pillar collapsing will increase exponentially over the coming years. The mining of all existing support pillars will increase the life of mine as well as result in a stable surface area being left behind. This will also result in the creation of a once-off underground water programme.

Surface soil erosion is destroying valuable agricultural lands. The subsidence creates uneven surface contours, resulting in enormous cracks from the surface straight into the old underground workings, resulting in vast quantities of soil going into the underground workings. The establishment of a grass-field before total extraction takes place will help to minimize the overall soil erosion process. No further rehabilitation will then required, other than steps to be taken to combat the soil erosion.

Subsurface soil erosion results in the creation of dangerous subsurface domes, which will collapse, leaving dangerous holes behind. The cracks caused by the subsidence then need to be filled with fine coal ash. The immediate treatment of the cracks caused by the subsidence will eliminate the possible occurrence of subsurface cavities and of soil entering the old underground workings.

Acidic mine water drainage is the term used to define drainage that occurs as a result of the natural oxidation of sulphide minerals contained in rock, which is exposed to air and water. The removal of oxygen in the old underground workings will prevent the water from becoming acidic. The displacement of oxygen by flooding the old underground workings with water will minimize any further acid-forming process.

After mine closure, uncontrolled polluted mine water will decant at various points. A wetland of purified water will also help to sustain more acceptable levels of pollution and acidity. The establishment of a man-made wetland in the south of the coal reserves can therefore be used to purify the mine water. The area will be large enough to create a well-balanced flow for an effective purification process and to handle the volumes of decanted mine water.

The proposed site is also suitable for use as a possible decant area. Horizontal drill holes near the wetland will prevent mine water from decanting in an uncontrolled manner into the environment. These drill holes, positioned at the same evaluation level of the wetland, will create a free flow, with little resistance for water to enter the wetland.