ABSTRACT
Mobile subsurface colloids have been found to influence the transport of contaminants significantly. In the absence of mobile colloids, many contaminants readily sorbs to immobile subsurface solid matrix and therefore the contaminants are virtually retained in the subsurface without getting into the groundwater, thus presenting little danger to groundwater supplies. Contaminants of various kinds of metals and radionuclides bind strongly to mineral components and particulate inorganic matter of the solid phase, while many nonpolar organic contaminants have a high affinity for binding to particulate organic matter (McCarthy and Zachara, 1989). In the presence of subsurface mobile colloids both the water flows and the transport of contaminants in the subsurface get considerably altered (Sen and Khilar, 2006). It is now generally accepted that there is always a part of the soil solid phase that is mobile under different geochemical and hydrodynamic conditions and that the mobile organic and inorganic subsurface colloidal particles may facilitate or retard the contaminant transport in underground soil (Honeyman, 1999; Kersting et al., 1999; Kretzschmar et al., 1999; Elimelech et al., 2002; Saiers, 2002; Sen et al., 2002a,b). This topic has been reviewed periodically, the recent one being that of Sen and Khilar (2006). This chapter presents a concise description of subsurface colloids and the colloid-mediated transport of contaminates transport in subsurface soil.
