ABSTRACT CTS-9523824 The overall goal is to understand the circumstances in which colloidal phases exist suspended in groundwater. It is hypothesized that mobilization of colloids, pre-existing as part of diagenetically produced coating and matrix within the aquifer deposit, is the most common and important source of such microparticles and macromolecules to the groundwater from aquifer sands. The particle-particle contacts present in aquifer sands that serve to immobilize colloids will be identified. The responsiveness of such attached surfaces to changes in solution composition will be determined, and the mobilization of colloids within intact in situ aquifer deposits when these are flushed by changed groundwater will be assessed. High resolution transmission electron microscope will be used to examine aquifer grain contacts on the nanometer scale. By exposing such well-characterized natural colloid reservoirs to defined aqueous solutions in the laboratory, the mechanisms by which the surface-surface attractive forces can be changed to repulsive interactions will be deduced. Small scale field injection/withdrawal tests using modified groundwater compositions, chosen based on the laboratory results, will be performed to assess the ease with which the colloids are detached in the field. Understanding the mechanisms by which colloid mobilization occur in groundwater is important for waste disposal activities and the movements of "pump-and-treat" type remediations. ***
