Water Quality Models for Analysis of Small System Operation: Case Study of Carthage, NC

Small systems are often plagued by a lack of resources, outdated equipment, unreliable raw water supplies, and minimally trained staff. A study has been undertaken to document the transition of a small system from conventional treatment to microfiltration. The Town of Carthage, North Carolina (population 2,300) completed construction in May 2002 of a 1.0-MGD microfiltration treatment plant. The study involves the analysis of monthly samples of raw water, finished water, and water collected at six different locations in the distribution system, both before and after the startup of the microfiltration plant. Water quality in the distribution system has been highly variable. To better analyze and interpret water quality data for this system, a water quality model of the distribution system was used to predict water age and disinfectant residual concentration. The model demonstrated that tank sizing and operation along with long retention times significantly affect water quality in the Carthage system.