2011 Annual Report 1a.Objectives (from AD-416) The overall objective of this project is to improve our understanding of and ability to predict the transport and fate of pathogenic microorganisms at various spatial scales (from pore to plot scale). 1b.Approach (from AD-416) Laboratory experiments will be designed to test specific hypotheses with regard to mechanisms controlling pathogen transport and fate in the environment. The specific experimental approaches and techniques will depend on the research question. For example, we may use measurements of electrophoretic mobility, hydrophobicity, surface charge density, enzyme treatment, FTIR, and TEM imaging to examine surface properties of pathogens that influence their interaction in the environment. We may use batch, micromodel systems, DLVO calculations, pore-scale flow and transport simulation techniques, and saturated and unsaturated column experiments to examine mechanisms of pathogen transport, retention, and survival. Information collected from laboratory studies will be used to refine and improve the predictions of models for pathogen transport and fate. Existing models for pathogen transport and survival will be modified to simulate field scale behavior. 3.Progress Report Laboratory and numerical studies were conducted to investigate the influence of physical and chemical factors on the transport of E.coli O157:H7 and coliphage fX174 through preferential flow systems. Preferential flow systems were created in 13.2 cm diameter and 20 cm length columns by embedding sand lens of various grain size, length, and vertical position into finer textured matrix sand. Tracer solutions containing bromide and microbes were prepared at different ionic strength (IS) and sprayed onto the surface of the columns at desired steady rates using a rain simulator to achieve saturated or unsaturated conditions. Effluents were collected at the column bottom continuously and analyzed for concentrations of bromide, fX174, and E.coli. Complementary numerical simulations were conducted using the HYDRUS 2D code over a wider range of physical and chemical conditions, and to analyze bromide and microbe transport in the columns. Results indicated that preferential transport of the microbes was dependent on the hydraulic contrasts between the matrix and lens, the length of the lens, the size of microorganism, and the water saturation. The IS also influenced the preferential transport of microbes. In particular, increasing retention with IS decreased the overall microbe transport but increased the relative importance of preferential flow. The above results compliment all three objectives of the parent project by improving our ability to predict the fate of pathogens in the environment and to assess management practice to minimize the risk of pathogens to food and water resources. In particular, transport of pathogens in runoff water will be strongly influenced by preferential flow and transport. The Principal Investigator coordinates research objectives and activities with UCR personnel, and meets with them on a regular basis to discuss progress.