Quantifying the significance of faecal contamination in Yarra River due to dry weather sewer spills
Creators: name: Tavate, Sainath
Publisher: name: RMIT University
Year: 2024

description: The Yarra River is considered to be an important environmental and recreational asset by the Melbourne community. The upper reaches of the Yarra River provide water for drinking and agricultural purposes whereas the lower Yarra is mainly utilised for recreational purposes. According to State Environmental Protection Policies (SEPP), the water quality in the upper reaches is higher compared to the lower reaches of the Yarra River.<br><br>The main objective of this study is to determine the significance of the dry weather spills on storm water quality and the microbes transported to the waterways. It was necessary to estimate the survival rate of microbes on pervious and impervious surfaces after a spill event. In addition, the spill data obtained from South East Water was examined to determine the impact of spill on the river water quality.<br><br>Field experiments were carried out at the Mt. Martha sewage treatment plant, Victoria. The experiments were carried out in summer and winter 2008, and summer 2009. Raw sewage was applied to each pervious and impervious surface to simulate a spill event. Samples were collected after simulated rainfall events at different time intervals. Samples collected were analysed for microbes (E.coli, enterococci and FRNA coliphages) and nutrients (Total nitrogen and Total phosphorus). The experiments indicated the presence of E.coli and enterococci organisms on pervious surfaces, even 15 days after a simulated spill event. In contrast, FRNA coliphages and nutrient concentration levels dropped significantly over time. The microbe levels observed on the impervious surface were very low.<br><br>Field experiments also demonstrated the variation of E.coli and enterococci concentrations within the collected samples. The concentrations of nutrients in the collected samples show no relationship to the availability of microbes.<br><br>Field data from winter 2008 and summer 2009 were used to develop a microbe prediction model. Multiple regression analysis was carried out using survived microbe concentrations, climate variables and elapsed time after a spill to predict the survival rate of E.coli and enterococci on a pervious surface after a dry weather spill. The climatic data of the nearest meteorological station was collected from the Bureau of Meteorology. A successful model was developed to simulate the relationship among microbes, elapsed time and average relative humidity. This relationship was validated using an independent set of data and the performance of the relationship was found acceptable. However, caution is recommended while predicting the enterococci organisms.<br><br>This predictive model was coupled with the simple microbial transport model to estimate the concentration at the stormwater drain inlet. The resulting output will provide the amounts of microbes to be present at stormwater drain. A relationship was developed between different storm events and the percentage of microbes transported towards stormwater drain. <br>