Summary Report on Transport of Contaminants in the Subsurface: The Role of Organic and Inorganic Colloidal Particles

A meeting on ''Transport of Contaminants in the Subsurface: Role of Organic and Colloidal Materials'' was held on October 5-9, 1986, in Manteo, North Carolina. The meeting was part of the series of International Seminars on the Subsurface held by the Subsurface Transport Program o f the Office of Health and Environmental Research of the U.S. Department of Energy. The meeting was organized by Frank Wobber (OHER/DOE) and John McCarthy (Oak Ridge National Laboratory). The purpose of the meeting was to review current knowledge about the role played by colloids on the mobility of contaminants in the subsurface environment, and to identify important long-term research needs in this area. Participants included senior researchers in this field from national laboratories, government agencies, universities, and research institutes in four countries. Recent findings on the occurrence and nature of colloidal material in the subsurface as well as on the association of colloids with organic, metal, and radionuclide contaminants were presented and discussed. Field studies have demonstrated that colloidal particles do move through aquifers and that radionuclides have been transported much further than predicted due to their association with mobile colloids in the groundwater. The consensus of the meeting was that colloids do occur in the subsurface environment, are capable of binding organic and inorganic contaminants, and do alter the mobility of Contaminants. A major difficulty in understanding and predicting the role of colloids is their heterogeneous nature that hampers precise chemical characterization. Clay and metal oxide colloids can be formed or dissolved due to changes in solution chemistry in the aquifer. Organic colloids have variable and diverse functional groups, making it difficult to predict their association with metal and radionuclide contaminants Some important advances were reported toward understanding the assembly of organic colloids and the nature of their interactions with organic contaminants. Major research needs identified by the participants included studies in real systems on the occurrence of colloids in subsurface environments, and more rigorous characterization of the physical and chemical properties of the colloidal material. Methods for sampling colloids need to be improved to avoid production of artifacts during collection. In summary, the meeting concluded that colloidal material is important in contaminant transport and that further research in this area will significantly improve our capacity to predict the movement of energy-related contaminants in subsurface environments