A Comprehensive Condition Assessment of a Critical Water Main

The city of St. Peters and the city of St. Charles, Missouri, created a joint venture (JV) to purchase finished drinking water from the city of St. Louis to supplement the water supply for the two communities on the north side of the Missouri River. The JV water pipeline is a critical component that provides these communities with water to meet their demands. The pipeline is a 36-inch ductile iron pipe (DIP) with a 2,000 foot 30-inch steel pipe that crosses under the Missouri River. The pipeline was installed in 1986 and is approximately 5 miles long. The pipeline has only had two leaks since it was constructed. Those leaks emphasized the critical nature of the pipeline and the consequences that a major failure would have, especially if the failure occurred under the river. The project included an evaluation of available inspection technologies capable of identifying and measuring pipe wall loss and detecting leaks. Indirect inspection methods were also con-sidered to evaluate the corrosion potential of the soil. This paper will review the process used to evaluate these technologies and explain why each was selected. The direct methods included electromagnetic (EM) technology to evaluate the integrity of the pipe wall, acoustics to identify leaks, and an external corrosion direct assessment (ECDA). The indirect methods included the use of Geonics and soil sampling to measure soil corrosion poten-tial. In addition to the condition assessment of the pipeline, the project included evaluating the flowmeter accuracy to determine if other unaccounted water loss issues existed in the system. The results of this project provided the pipeline owner with a comprehensive evaluation of the pipeline condition. The effort identified seven leaks and two wall loss defects, potentially indicative of pipe wall corrosion under the river. The leak detection helped resolve water loss concerns, which could not be accounted for in previous flowmeter data. The inspection was conducted using best-in-industry technologies to gather the data required to evaluate the pipe and the data to determine if repair, rehabilitation, or a secondary pipeline crossing under the river was needed.