AWWA ACE95288

AWWA ACE95288 Modeling of THM in Water Distribution Systems - Charlotte Mecklenburg Utility Department
Conference Proceeding by American Water Works Association, 01/01/1995

Townsend, Jacqueline A.; Tripp, Sandra L.

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Like many surface water users, Charlotte Mecklenburg Utility Department (CMUD) is concerned with the water quality changes ultimately seen in its water as it progresses through treatment into the distribution system and finally to the customer's tap. Trihalomethane (THM) formation, in particular, is an inherent problem seen in distributions systems employing surface water sources. Also of concern is the accompanying decay of chlorine residual seen in high THM formation potential water. There are three areas at which CMUD can take measures to control THM formation. The first is at the water supply. Watershed management and protection techniques can be employed to control the presence of the organic precursors needed for THM formation. The second area is at the treatment plant. Treatment processes resulting in more efficient precursor removal and/or modification of disinfection practices can be implemented. The final area is in the distribution system. CMUD has been utilizing computer hydraulic models to analyze its distribution system. They had been able to size distribution water mains to meet future system demands, but were unable to determine how water quality would be affected by future changes. CMUD needed a tool to help identify possible water quality problems in the system. With the upcoming changes in the drinking water regulations, CMUD felt there was a great need to have the capability to better look at water quality parameters. In 1993 Boyle Engineering began work on a Water Master Plan for the Department. This many faceted study included hydraulic distribution system modeling, water quality distribution modeling, surge modeling and integration of a facility management system including GIS integration. The water quality modeling would be based on the hydraulic model of the water mains sized 12-inch and larger. Although the accuracy of the water quality model would be a satisfactory first step for establishing trends and determining general problem areas.