The long-term impact of intermine flow from collieries in the Mpumalanga Coalfields

[摘要] English: Mines fill up with water after closure. As a result, hydraulic gradients developbetween them and different hydraulic water pressures are exerted onto peripheralareas or compartments within mines. This results in water flow between mines, oronto the surface. This flow is referred to as intermine flow. Intermine flow as aconcept includes the quantity and quality of the water.The significance of this project lies in:�?The establishment of a Geographic Information System (GIS), detailing thevarious aspects around intermine flow for the Mpumalanga Coalfields.�?The identification and discussion of management options to minimise thelong-term impact of intermine flow on the environment.�?The provision of this information to the industry and government for theassessment of future liabilities and impacts.The total area investigated constitutes 26 000 km2 with the mine lease areasamounting to 4250 km2�?This covers all of the collieries in Mpumalanga Provincefrom where information could be obtained.Information available in the South African coal-mining industry suggests that mines fillup with water and decant after closure. This usually occurs within 10 y. At the moreisolated collieries, rebound of the water level may take up to 50 y. Apart from the factthat mine water is saline, low pH-values may also be encountered.Mining has been on all five coal seams in the area. Statistics on mined areas areprovided below: See table in full text.Sufficient connectivity exists between mines and the surface to allow interflow of minewater. These connections are in the form of opencast mining, shafts, prospectboreholes and subsidence structures.Interflow of water on coal seam levels is also possible in most of the collieries due tothe extensive nature of mining, particularly in the Witbank and Secunda areas.Pathways in mines dictate flow of underground water, rather than natural flow paths.Many critical areas of potential intermine flow have been identified, where significantquantities of mine water will transfer from one mine to the other.The combined impact in terms of anticipated water that will be available for interflawor to decant from the various mines is in the order of 360 MLld with a sulphate load of660 t/d. For illustrating the significance of these volumes, the total volume to decantfrom these mines is in the same order as the annual natural run-off into the WitbankDam. The range of quantities and qualities for individual mines will vary significantly,depending mainly on the mining method employed. Many other site-specific factorsalso play a role. Management options to cope with intermine flow are applicable oneither a catchment or mine basis. Those on a catchment basis are:•The reduction of the number of decanting points through the interconnectionof mines.•The control of decanting positions through interconnection of mine workings.•The conjunctive treatment of decanting mine water at convenient locations.On a mine basis, the following actions will markedly reduce the volume of water orthe amount of salt to be discharged:•Design long-term water management schemes taking cognisance ofneighbouring mining activities.•Design the mine lay-out to retain as much of the mine water as possible in theunderground workings whilst mining.•Investigate coal barrier characteristics and design coal extraction accordingly.•Minimise water ingress into mines to reduce water volumes, if required.•Mix mine water of various qualities to achieve the best possible quality beforeflood discharge.•Minimise salt loads by:•Flooding mine workings as soon as possible.•Flushing flooded mines.•Utilising the natural neutralisation potential of the coal and rock.Examples of intermine flow already exist on an alarming scale in the Mpumalangacollieries. This study shows its impact on surface and also at barrier pillars inindividual collieries. Mines should incorporate mine-water interflaw into their planningphase and ensure that this fits in with activities of their neighbouring mines.

[发布机构] University of the Free State