AWWA ACE95088

This paper summarizes the results of an American Water Works Association Research Foundation (AWWARF) sponsored study to characterize and model chlorine decay in distribution systems. The primary goal of this study was to gain a better understanding of the kinetic relationships describing chlorine decay and trihalomethane (THM) formation in water distribution systems and to make available to the water utility industry improved water quality simulation models. The study included an extensive program of field sampling studies to provide data for validating alternative kinetic models. Concurrently, laboratory research on the effect of water quality parameters on chlorine decay and laminar flow chlorine decay models was performed. Several kinetic models were evaluated, tested, and validated using data collected in the field sampling studies conducted at the participating utilities. The results of these studies indicate that chlorine decay in distribution systems can be characterized in most cases as either first order decay in the bulk liquid or as a combination of first order bulk and first or zero order decay reactions at the pipe wall. These kinetic models are being implemented in the EPANET distribution network model, a public domain software package developed and distributed by EPA and available to the water utility industry. The focus of this paper is on the analysis of the results of the US field sampling studies and the evaluation and testing of chlorine decay models.