ABSTRACT
Contaminant properties and subsurface conditions that result in interactive processes often cause the rate of contaminant transport to differ from the rate of ground water flow. This chapter considers abiotic (nonbiological) processes active in the subsurface. Sorption and desorption are two major mechanisms affecting the transport of contaminants in the subsurface. The adsorption attachment may be the result of one or a combination of electrostatic forces. Hamaker and Thompson (1972) include the following as electrostatic forces between chemicals and soils: van der Waals/London forces, hydrogen bonding, charge transfer, ligand exchange, ion exchange, direct and induced ion-dipole and dipole-dipole interactions, and chemisorption. Equilibrium sorption assumes that the rate of sorption is relatively fast (compared to the rate of movement of ground water); hence, solution residence times sufficient to establish equilibrium exist. When nonlinear isotherms are evidenced, it should be noted that the isotherm may still be linear at low concentrations.
