A model study has been conducted to understand the influence of hydrodynamic features, environmental conditions as well as bather shedding and animal fecal sources on the fate and transport of indicator microbe enterococci at a subtropical marine beach in South Florida. The model being used is based on an existing finite element hydrodynamic and transport model CAFE3D to which a first order microbe deactivation function due to solar radiation is added. The decay coefficient is assumed to be linearly proportional to the solar insolation value, while the constant coefficient linking the two is determined to be 0.368[m2/MJ] using local experimental data. This value corresponds to decay coefficients in the range of 0 to 1 hr-1 and is of similar magnitude to values found in the literature. The hydrodynamic model produces water current velocities, which are used in the transport model to simulate water enterococci concentration in space and time. Previous measurements have suggested that enterococci originate from the beach shoreline area. In this case the simulated velocity fields and Lagrangian particle trajectories indicate that the small velocity (generally less than 0.05m/s) and weak dilution at the water?s edge may cause enterococci accumulation and elevated concentration. Among human and animal sources, the impacts on maximum enterococci concentration in descending order is a dog fecal event, human bather shedding and seagull fecal events. A single dog fecal event at the middle part of the beach is found to cause enterococci far field concentrations to reach hundreds of CFU/100ml, which exceeds the EPA water quality standard (104 CFU/100ml). These high concentrations, however, only impact a small area. Concentration due to tens of bathers shedding enterococci during a course of 4 hours reaches 0.01 CFU/100ml, while the concentration due to thousands of bather shedding during a Memorial Day weekend reaches about 1 CFU/100ml. Concentration due to tens of seagull fecal events reaches only 0.0001 CFU/100ml. Thus, only the presence of dogs could explain the high enterococci observations infrequently found in monitoring data. The limited spatial extent compared to beach survey data of the enterococci plume from a dog fecal event suggests that other microbial sources are present, most likely microbes released from the beach sand.

A scarcity of comparable research on the transport of bacteria has forced hydrologic models to assume that bacteria travel as dissolved chemicals. In reality, most bacteria preferentially attach to soil aggregates, and behave very differently from planktonic bacteria. The goal of this research project was to identify and evaluate a laboratory method for partitioning between attached and planktonic bacteria that could be used to improve hydrologic modeling. Attachment was measured indirectly as the difference between total and planktonic bacterial concentration. Planktonic concentration was defined as the concentration of bacteria that could pass through an 8 μm screen. Total concentration was determined by disaggregating attached bacteria through a dispersion treatment. A randomized complete block design was structured to test for the effects of filtering, two dispersion treatment options, and the presence of soil on concentration. Tween-85 surfactant was selected as the best dispersant for use in further studies. About 78% of bovine <I>E. coli</I> in the laboratory samples were adsorbed/associated with sterile soil particles. Twenty samples of different bacteria-soil ratios were analyzed using this method to develop an isotherm equation describing <I>E. coli</I> partitioning. The <I>E. coli</I> used to inoculate these samples was cultured using a chemostat reactor to control cell growth stage and control variability. A linear isotherm (R²=0.88) was selected to describe this experimental data; however, future studies characterizing the partitioning behavior of <I>E. coli</I> under different environmental conditions are recommended in order to better understand attachment prior to modeling attached and planktonic <I>E. coli</I> separately. / Master of Science

Reusing stormwater is a sustainable approach that a lot of cities around the world, including cities in Canada, are developing to improve local and regional water resources. For this purpose, water is typically withdrawn from stormwater ponds (large urban infrastructure that retain stormwater) and used for applications that require less than pristine water quality. However, the large size of these ponds along with the heterogeneity in water quality internally, make the withdrawal location from these ponds for reusable stormwater critically important. Also due to the large sizes of these ponds, collecting data throughout the pond to determine the optimal location for withdrawal is not practical. Modelling however, can provide a more practical means of studying contaminant distribution within the pond over time in order to identify the withdrawal location, among other valuable information. In this dissertation, a modelling approach was developed that simulates fate and transport of bacteria in stormwater ponds after rainstorm events. The model was run to simulate bacteria in the Inverness stormwater pond, which is a large T-shaped pond located in southeast of the City of Calgary, Alberta, Canada. The model has two components: a hydrological component and a Computational Fluid Dynamics (CFD) component. The hydrological component calculates the stormwater runoff of the subbasins of the catchment draining into the pond. The results were compared with collected data and good agreement was observed. Then, the results were fed to the CFD component as input in order to simulate the distribution of contamination brought in by the local hydrology. The CFD component simulates the hydrodynamics of the pond 3-dimensionally. The model was run based on collected data from the pond and multiple versions of the model were developed with regard to free-surface and particulate-attached bacteria transport. In order to address a common issue with hydro-environmental models – being difficult to validate - the model was validated in two ways. First, an instrument was designed and built to measure fluid flow velocity magnitude and direction in the pond. Once calibrated, it was deployed to the pond and the flow field was measured at multiple locations for validation purposes. Second, a non-dimensional number was introduced allowing a comparison between the bacteria concentration data from collected data and that of modelling result in multiple locations of the pond. In both of the validations, good agreement with collected data was observed. A volume of Fluid model and sediment transport model were integrated into the model, which allowed consideration of free-surface effects and for modeling wider range of bacteria, respectively. The model was used to identify the optimal location for water withdrawal for reuse. The middle of the pond, where the three wings join and near the surface, was located as the optimal location due to the lowest bacteria concentration. In an attempt to improve the water quality in the optimal location, strategic tree planting on the north bank of the West wing was studied. It was shown that the trees can reduce the transport of bacteria from the most contaminated location to the withdrawal location. The model was also used to study the impact of some of the important assumptions and environmental factors, such as rain and wind, on bacteria distribution. Wind was found to play a crucial role in the bacteria distribution in the pond. / Graduate