A Probabilistic Approach to Control Toxic Solute Transport in Fractured Mined Rocks

Changing rock structure caused by long-term coal extraction in Donbass (Ukraine) accelerated water and mass exchange in mining areas dramatically. There were appearances of toxic substances in underground workings due to spills on near-by chemical plants having affected the personnel. These accidents prevention needs reliable estimation of water and mass flow in fissured rocks transformed after mining. Efficiency of the emergency warning system can be essentially increased by using the predictive flow and transport models.

A probabilistic approach appears to correspond better to highly heterogeneous fissured strata, especially under the lack of the monitoring data near abandoned workings. The developed model describes water flow and solute transport in systems of channels generated stochastically as chains of broken lines according to distributed and fracture parameters changing in space. Flow velocity depending on the fracture width is considered as the distributed parameter. Summarizing local velocity distributions yields the global distribution for several fracture systems. It allows estimating water inflows into adjacent workings separating contribution of different sources on the surface.The velocity distributions used together with the 1D transport model determine variations of concentration as the random function. Two stages of migration are simulated consecutively, firstly in fractures and then in open water flows on the working bottom. The resulted function is the concentration of substances in pumped mine water collected from different horizons of mining.

The model was calibrated using the data about tracer migration in Central Donbass. Inverse modeling has confirmed high transport velocity reaching 600 m/day and variation of tracer concentration in different mines. The model can be used in estimation of dangerous zones in worked out strata near hazardous sites and control of mine water pumping and discharge to localize spreading toxic substances in ground and surface waters.