Natural processes controlling the behaviour of contaminants in ground-water

Abstract

The concentration and migration of contaminants in ground-water is influenced by many geochemical, physical, and biological processes.The mobility of inorganic and organic contaminants in ground-water is controlled by their solubility. The dissolution and precipitation behaviour of many substances can be predicted with help of geochemical models on basis of chemical thermodynamics. The adsorption of contaminants on the surface of solid particles and the desorption of other components into solution cause a retardation of contaminant transport with respect to surrounding groundwater. The empirical distribution coefficient as characteristic measure for this process is specific for the given contaminant and the geochemical environment.Convection and hydrodynamic dispersion control the transport and the mixing processes of contaminated ground-water with natural ground-water. The concentration of the contaminants decreases in time and with transport distance whereas the volume of the contaminated plume increases. The specific properties of immiscible organic fluids, e.g. mineral oil products and chlorinated hydrocarbons, result in lower or higher flow velocities than that of water and in the tendency to form separate impregnation bodies on the water table or at the base of the aquifer. Gas transport is important for the removal of volatile contaminants and decay products. The transport of suspended particles is controlled by filtration processes.Organic compounds are decomposed by autochthonic microorganisms that obtain from these processes carbon and hydrogen for their cell synthesis and energy for their metabolism. The main effect of microbial activity is an acceleration of geochemical processes. The propagation of pathogenic bacteria and viruses in ground-water is controlled by the same general mechanisms as that of the other contaminants. However, the active attachment and mobility of bacteria may improve the effectivity of the specific processes.