Assessment of how water quality and quantity will be affected by mining of the Waterberg coal reserves west of the Daarby fault

The Lephalale region of the Waterberg contains the third largest coal reserves in South Africa and can become a new powerhouse for coal-fuelled electricity production in the country. It is unknown how many additional mines are planned for the study area, but it is doubtful that there will be such a large number of pits that they will change the surface topography to such a dramatic extent that they will change the flow direction of surface runoff. Efforts should be made by all parties to minimise the amount of damage done to the environment. This will be challenging, as all the mines located in the study area will be open-pit mines. This requires the removal of overburden, plants and animals from the pit location. An effort should also be made to safeguard the endangered species that inhabit the area in question. Due to the planned expansion of the mining enterprises in the area and the accompanying developments, it is important to determine the extent of the impacts these developments will have in the area. This study looked specifically at the impacts these developments will have on the groundwater quality and quantity in the area. The project was conducted in several stages, beginning with two hydrocensus to locate as many boreholes in the area as possible. Water levels, borehole depths, location and EC and pH were measured and groundwater samples collected. Other data were gathered from Exxaro, Sasol and Eskom and compiled into a database used for contour maps, the determination of recharge, etc. Tests in the field determined the aquifer parameters of the different aquifers present in the study area. To account for influx of water to the study area, the recharge for the study area was calculated by means of the Chloride Mass Balance method and the E.A.R.T.H. model. These calculations indicated a low recharge for the area. To determine the acid potential, acid-base accounting (ABA) was performed on the collected samples; the tests indicated that most of the samples collected would become acidic upon oxidation. To form a more complete conclusion of the potential impact of mining of the coal field samples were collected from the beneficiation plants at the Grootegeluk mine. These samples were also analysed for acid potential, the results of which indicated that the samples will become acidic upon oxidation. Numerical modelling was used in order to determine the impact the mines would have on the groundwater and the flow directions of the groundwater. The dewatering models indicated that there very little water was available in the study area with small volumes predicted to flow into the mines. The decant models indicated that there was no possibility of the pits ever reaching decant levels with the highest recorded rise being seven metres, 50 years after mining had stopped.It was concluded that the most effective way to preserve the water quality and protect the groundwater quality from further deterioration was to keep all acid generating material dry as it would not be possible to flood this material once the mine closes, due to the small volumes of water in the area. The volumes of water that will enter the mines from groundwater and surface runoff will be small, hence it is recommended that the water be pumped out and used for run of mine operations such as dust suppression or washing of the ore. Steps should be taken to minimize the risk of encountering a fault during mining. If the mines encounter large faults and start to dewater the faults, many farmers with boreholes along the length of the fault might see significant decline in the water levels of their boreholes. It is recommended that preventative measures be taken rather than containment for the new mines planned for the area. It is recommended that the methods of mining, beneficiation, remediation and water management currently being employed by the Grootegeluk mine be employed by the new mines. The methods being used at the Grootegeluk mine have been proven to be the best possible solutions for the conditions found in the area.