Contaminant Propagation in Distribution Systems

Abstract

The Safe Drinking Water Act (SDWA) of 1974 requires that the U.S. Environmental Protection Agency (EPA) establish maximum contaminant levels (MCLs) for each contaminant which may have an adverse effect on the health of persons. The SDWA clearly specifies that these MCLs shall be met at the consumers tap. Nevertheless most regulatory concern has been focused on water as it leaves the treatment plant before entering the distribution system. There is, however, growing interest in determining the factors that cause water quality variations in drinking water distribution systems. In order to study this effect, the Drinking Water Research Division of EPA initiated a cooperative agreement with the North Penn Water Authority. This cooperative agreement has resulted in a series of field monitoring and systems modeling studies that lend insight into the movement of contaminants in distribution systems. Previous research has resulted in development of a steady-state model, a quasi-steady-state model and dynamic model that have provided useful approaches to modeling the general propagation of contaminants in distribution systems. In this paper, results from the steady-state model are utilized to examine the actual pathways of water flow and the time of passage and percentage of water that flows from a given source to a given node in a distribution system. The contaminant propagation technique developed from this extension of the steady-state model provides a useful technique for analyzing many of the factors that affect water quality in a distribution system. A major finding of this research study is the importance of adequate hydraulic modeling of the systems being studied and the importance of field studies in verifying systems performance. The approach suggested in this research will provide useful insight into the water quality variations that may impact consumers at the tap and the development of time and spatially sensitive monitoring strategies.