2006 Annual Report 4d.Progress report. This report serves to document research conducted under a Reimbursable Interagency Agreement between the USDA-ARS and USDA-CSREES. This project has recently been approved for funding by the National Research Initiative of CSREES. The projected start date is anticipated to be 8-1-2006. The USDA-ARS parent project number is 5310-32000-002-00D and is entitled “Detection, Source Identification, Environmental Transport, Fate, and Treatment of Pathogenic Microorganisms Derived from Animal Wastes”. At present our ability to predict the transport and fate of pathogenic microorganisms in natural subsurface environments is limited by our understanding of the pathogen deposition process. A review of the literature indicates that the current paradigm for pathogen deposition, filtration theory, has serious flaws because it does not adequately account for the combined physical and chemical removal mechanisms involved in small pores and at grain-grain contacts, at colloid-colloid interfaces, and at colloid-grain interfaces. Therefore, the overall objective of this proposed research is to establish a clear understanding and ability to predict the physical and chemical mechanisms that are controlling pathogen fate in porous media. We expect to initiate research starting on 8-1-2006, once CSREES transfers funds to USDA-ARS for this project. We believe that the accomplishment of our research plan will significantly improve our ability to assess and predict the transport and fate of pathogens in subsurface environments. This information will also facilitate the development of improved animal waste management practices to minimize pathogen contamination of water resources, and thereby help safeguard drinking water supplies. Anticipated results are also expected to aid in the design and development of efficient and cost effective water treatment options for pathogens based upon soil passage and will serve as a foundation for quantifying the fate and movement of other colloid-associated