Predicting between-event variability of escherichia coli in urban storm water

Understanding microorganism levels in urban runoff is essential for appropriate storm-water management, especially when storm-water is utilized by humans. An Escherichia coli monitoring program was conducted at four urban catchments in Melbourne, Australia. Simple and multiple correlation analyses were conducted that related climatic, rainfall, storm-water runoff, and other water-quality characteristics with the event mean concentrations (EMCs) of E. coli. Also, several existing and modified storm-water-quality models were tested against the measured storm-water E. coli levels to determine whether existing storm-water models could be used for prediction. The key findings are that source, growth, and removal of microorganisms are more important than wash-off and transport processes during wet weather since the most influential factors for E. coli EMC levels are (1) antecedent catchment conditions, such as vapor pressure prior to an event; (2) nutrient levels in storm water, such as ammonium, total phosphorus, and total nitrogen levels. However, rainfall intensity, which was found to be the most important transport-related variable (although less significant than the aforementioned build-up parameters), may also be considered in EMC prediction.