Investigation into the groundwater interaction between a deep coal mine and a deeper lying gold mine

[摘要] After the closure of mines, it is expected that water in the mined-out areas will flow alongpreferred pathways and accumulate in lower-lying areas (Grobbelaar, 2001). Over time, theseman-made voids will fill up with water and hydraulic gradients will be exerted on peripheral areaswithin mines, resulting in groundwater flow between mines and possibly surface. This flow isreferred to as intermine flow (Grobbelaar, 2001). Due to the potential long-term impact ofintermine flow in terms of water quantities and qualities, the Department of Water Affairs andForestry regards intermine flow as one of the most important challenges in the mining industry.Hydro-chemical and stable environmental isotope sampling were used to determine theinteraction between the Karoo aquifer and the Witwatersrand aquifer. Comparison between theresults showed that there is interaction between the Karoo and Witwatersrand aquifer, bothwhere coal mining is present and where coal mining is not present.As the coal mine in future will cover most of the gold mining area except for the central part ofthe study area, it is expected that groundwater affected by the coal mining in the Karoo aquiferwill move along naturally occurring structures from the base of the Karoo aquifer into the goldmine workings if preferential pathways are encountered. This interaction can directly link to thenumber of structures that are water-bearing in the study area and are covered by coal miningactivities. From the field work done in the underground gold mine, the number of structures thatare water-bearing are the exception rather than the norm. Therefore the potential forgroundwater interaction from future coal mining into the gold mine will be low.1Based on current inflow rates, the gold mine workings will take approximately 406 years to floodand reach the bottom of the coal mine workings. It is highly unlikely that this flooding will decantonto the surface through the coal mine, as the shallowest coal mine workings are at 39 m belowsurface in the study area. In the unlikely event of decanting, polluted water originating from themining cavities will seep out as normal unpolluted springs at low points.

[发布机构] University of the Free State