Sensitivity of contaminant spread to decay rate in water distribution systems with implications for the spread of emerging contaminants

‘Emerging contaminants’ are newly introduced into the environment through release into surface waters from wastewater treatment effluent, manufacturing, and agricultural use. How emerging contaminants move through water systems is unclear. Since the decay rates of emerging contaminants in piping systems have not been determined, this study determines the importance of decay rate on concentration throughout a distribution system and also determines how the system layout effects concentration. Systems were modeled to determine the time to peak contamination for a clean system becoming contaminated, as well as a contaminated system being cleaned of contamination. It was found that only emerging contaminants with second-order decay at the highest rate observed did not build up to high concentrations. The position of storage tanks in the distribution system affected the rate at which contaminants cleared the system, and systems with a branched layout could be cleared of contamination faster than systems containing loops.