NUMERICAL MODELLING TOXIC SUBSTANCE TRANSPORT IN MINE WATER FLOWS

Abstract

The purpose of this work is to develop and test a methodology for modelling the migration of toxic substances left after mining in mine water flows in a system of hydraulically connected mine workings of various sizes and elevations depending on the drainage parameters. Methods of research include the analysis of factors that influence the formation of the hydraulic regime in flooded mines, the accumulation and transport of toxic substances. Parameters of moving toxic substances in mine waters are calculated using hydraulic flow equations written for mining workings, with flooded workings being considered as pipelines with distributed recharge. Modelling of non-stationary 1D transport in water from local sources of toxic substances was performed using the finite difference method. Results. Flow rates and velocities in flooded mine workings on two hydraulically connected horizons of different elevations were calculated. For different locations of sources of toxic substances on the example of polychlorinated biphenyls, their concentrations in mine waters along the migration path and at the water hoisting at different flow rates were calculated. The influence of increased water withdrawal, dilution with additional recharge along the migration path and the position of potential sources of substances in the flooded mine were investigated. It wasshown that for the considered example, increasing the water outflow rate by two times accelerates the stabilisation of mass transport with an increase in the daily removal of substances by 3.4–6.4 times, which is more active from the upper horizon. Scientific novelty. For the first time, the transport of substances in flooded workings was simulated by combining a hydraulic flow model with a numerical transport model. Unlike 2D and 3D numerical transport models based on solid mechanics, which average the concentration in the grid blocks, the proposed approach allows the reproduction of the geometry of the mined-out space more accurately. It provides a more realistic distribution of flow velocities and concentrations depending on the parameters of the mine water withdrawal, depth of mine workings, and the mine water level. Practical significance. Using the tested methodology will make it possible to perform engineering predictions of the quality of groundwater and surface water near closed mines for different periods at different levels of flooding, water withdrawal rates and depths of the pumps for mine water drainage. In addition, the proposed technique can be used to justify the conceptual scheme of the numerical hydrogeochemical model of the post-mining areas. Keywords. Close mines, toxic substances, flooded workings, hydraulic flow, water hoisting, transport model.