Groundwater resource assessment of the Waterberg coal reserves

[摘要] English: The Waterberg coalfields represent the last area in South Africa, which contain largequantities of coal resources. According to Dreyer (pers. comm. 2009) the Waterbergcoalfields contain nearly 50% of the remaining coal resources of South Africa. Given the great demand for coal both local and abroad, primarily to be used as a fuel source for the power generation, the Waterberg coalfields have been targeted for large scale developments in order to exploit the coal. The primary method for exploiting coal is through mining. Mining, in any setting and any location has a diverse and often very serious impact on the environment. A scoping level study was under taken in order to determine the effect the mines will have on the groundwater resources and the pre-mining conditions of the aquifers and the quality of the groundwater. At present there is one operational colliery in the study area, the Grootegeluk mine. This mine has been in operation since the 1980's and has had a well-planned and operated monitoring system in place since the beginning of mining operations. This mine was used as a model to determine the impact new mines will have on the area. From the investigations it became apparent that the coalfield is situated in the Karoo Supergroup geology with the Mokolian Supergroup being represented in the study area by the Waterberg group quartzites. The coalfield is delineated by three major geological structures, the Daarby-, Eezaamheid- and the Zoetfontein faults. With the Daarby- and Eenzaamheid faults being impermeable according to Dreyer (pers. comm. 2009), The Daarby fault serves to divide the study area into an area west of the fault with shallow coal and an area east of the fault with deeper coal. Only the shallow coal will be mined. According to Dreyer (pers. comm. 2009), all of the planned infrastructure for the new mines will be located on the Waterberg group rocks south of the Eenzaamheid fault or on the Karoo rocks east ofthe Daarby fault. To determine the impact the mines would have on the groundwater of the study area, aquifer parameter testing (pumping test and slug tests), water quality determinations (inductively coupled spectrometry), acid-base accounting and numerical modelling were conducted. The results of the aquifer testing indicated low yielding aquifers with the harmonic mean of the transmissivities indicating a low transmissivity of 0.4 m2/d. In addition the recharge for the study area was calculated by means of the Cl and E.A.R.T.H. methods, resulting a value of 1.5% for the area. The average water level for the area was found to be approximately 28 m. The water quality determinations for areas that had not been affected by mining, indicated waters that had high EC values, near neutral pH value and medium to high Cl and sulphate values. The areas that have been affected by activities such as power generation and mining, displayed higher EC, Cl, and sulphate values than the unaffected areas. To more accurately determine the impact the mines would have on the area, numerical modelling was done. Three scenarios were simulated using similar parameters to determine the expected inflow into the mines and whether the mines would ever decant. The results indicated that the worst possible scenario there was an influx varying between 755 m3/d and 1283 m3/d depending on the location of the pits. For the decant models, 50 years after mining had stopped there was a rise of 3 m in the pits themselves. With the pits being simulated being 110 m deep it is concluded that the mines in the area will never decant. The results of the project indicate that the addition of new mines to the area will have an effect on the groundwater quality and quantity and steps should be taken to minimise this as much as possible.

[发布机构] University of the Free State