COLLOID MOBILIZATION AND TRANSPORT IN GROUNDWATER

Recent held and laboratory experiments have identified colloid-facilit ated transport of contaminants as an important mechanism of contaminan t migration through groundwater. For colloid-facilitated transport to be important, three criteria must be met: (1) colloids must be generat ed; (2) contaminants must associate with the colloids; and (3) colloid s must be transported through the groundwater. Significant progress in the understanding of colloid generation (by mobilization of existing colloids) and transport (limited by deposition) in model colloid and c ollector systems has been made in the past few decades. This knowledge of the model systems, however, is inadequate for prediction of colloi d behavior in natural groundwater systems. An understanding of colloid behavior in natural systems is essential for predicting the potential for colloid-facilitated transport in a given groundwater. This review presents theories describing colloid mobilization, deposition, and tr ansport, laboratory experiments in model systems designed to test thes e theories, and applications of these theories to colloid mobilization and transport experiments in natural groundwater systems. Emphasis is placed on mobilization of existing colloids by chemical and physical perturbations, the kinetics and dynamics of colloid deposition (filtra tion) and the ''blocking'' effect, and the effect of surface chemical heterogeneities on colloid deposition and transport.