PARTICLE TRACKING MODEL OF CONTAMINANT IN A FLOW THROUGH A POROUS MEDIUM TO DETERMINE CONCENTRATION AND DECAY

The transport of contaminants in porous media from localised sources such as factories and agricultural farms is a hydro dispersion phenomenon that has been a major topic for more than four decades. Inorganic wastes, primarily non-biodegradable substances from oil spills, human wastes, fertilisers, and other sources, percolates through porous media and eventually finds its way to water bodies and food crops on farms as a result of industrial and agricultural activities.  Some of these substances are harmful to human health and gets to our bodies through the water we drink or the food we eat. This research study aims to formulate a particle tracking mathematical model of contaminant flow through a porous media. The governing equation of three-dimensional concentration distribution in fluid flow through porous media has been formulated using advection-dispersion equation. This equation has been solved analytically and numerically using three-dimensional Finite Difference Algorithm. Simulation to validate solutions is done using data from agricultural chemicals as the source point. Results confirm that the concentration of one time source of contaminant decreases as it diffuses away from the source point with respect to distance and time. The plume evolved horizontally and vertically, with peak concentration at the source, and decays further and downwards due to degradation, reaction and sorption. Particle concentration tracking shows that concentration of 100mg/l at a point source decreases to 0mg/l, after a distance of 300m. For a toxic chemical like sulphur dioxide, glyphosate, and trinidol, if released from a point near borehole or food crops less than 300m, the contaminant can be traced to the drinking water and edible parts of the crop and accumulation in the body may be carcinogenic or cause kidney and liver infections. We recommend that for water pollution minimization, and safe food crops, the source of contaminant should be more than 300m. Additional reaction methods can be used to decompose the contaminant before reaching unwanted places.