Evaluation of management options for intermine flow and associated impacts in the Central Witbank Coalfield

[摘要] English: Research into the identification, quantification and impact assessment of theintermine flow on the groundwater and surface water quality of the Witbank andHighveld coalfields was undertaken as part of broader research initiatives The studyarea of this thesis included the coal collieries of the Central Witbank Coalfield.Intermine flow areas were previously identified in studies by Grobbelaar et al., 2001and Grobbelaar, 2001.The aim of this thesis was to develop a quantitative prediction of long-term intermineflow in the central Witbank coalfield, using the available data collected in the project.From the quantification of these flows and different hydrochemical techniques, likelywater quality profiles at these collieries were determined. The quantification on theintermine flow direction as well as the flow volume was predicted through numericalgroundwater modelling using Modflow. Local and regional models were comparedand it was found that regional models (relative to including the whole extend of thevoids in the model area) yielded the most accurate answer of the two models in thestudy area. The quantification of the predicted impact on water qualities was donethrough the use of mass balance approximations and an empirical sulphategeneration rate method (developed in this study for predicting future sulphateconcentrations in underground workings) using available hydrochemical and acidbase accounting data. It was calculated that the sulphate generation rate for theunderground workings is in the order of 0.1 - 1.5 kg/ha/d depending on the degreeto which the void is filled. An evaluation of water management strategies, which willminimise the long-term influence of intermine flow on the groundwater and surfacewater quality, was also done. A compartmentalization system to mining opencast pitshas been suggested for opencast pits with low decant elevations, to inundate amaximum percentage of the spoils to limit AMD reactions. The implementation ofartificially created, high recharge areas on opencast pits and underground workingsalso was investigated to reduce fill-up times of voids as to limit the exposure ofoxygen to the acid generating materials.The research indicates that intermine flow can be potentially detrimental to thegroundwater- and surface water systems depending on the flow volumes and qualityof the intermine flow water in the Central Witbank Coalfield. Flow volumes predictedthrough numerical modelling was quantified to be considerable enough to bepotentially detrimental to mining voids into which the intermine flow water flows. Itwas also found that the intermine flow could influence the fill up times of the miningvoids (both opencast pits and underground workings). The evaluation of differentmanagement options identified viable alternatives to manage intermine flow in sucha way as to yield future optimal water qualities for the Central Witbank Coalfield.

[发布机构] University of the Free State