AWWA INF52158

The East Bay Municipal Utility District (the District) supplies water treatment for twenty communities in Alameda and Contra Costa Counties in California. Approximately 1.1 million people are served by the District's water system. The water distribution system includes five water treatment plants, over 150 pumping plants, over 160 storage reservoirs and over 3,950 miles of distribution pipelines. These pipelines range in size from 2 inches to 96 inches and are comprised of a number of materials including steel, polyvinyl chloride (PVC), cast iron (CI), asbestos-cement (AC), and ductile iron (DI). Some of the pipe in the system is over 90 years old and the median age is 31 years. The system experienced two significant growth periods, one in the 20s and 30s and the next in the 50s and 60s. Pipe installed during the first period was predominately CI, without lining and coating. The AC and CI pipelines make up the highest percentages of pipe material in the system at 29% and 38% respectively and represent some of the oldest pipe. The DI pipe is responsible for 80% of the leaks. The District was concerned that the DI pipe will start displaying a failure frequency that is a function of its age. This paper will explain the methodology the District has developed to determine how much pipe it needs to replace to keep annual leak rates constant and the methods used to decide which pipelines should be replaced each year. Includes figures.