Water Transmission Main Condition Assessment in the Last Frontier: A Magnanimous Endeavor for the Anchorage Water and Wastewater Utility

The Anchorage Water and Wastewater Utility (AWWU) owns, operates, and maintains a water pipe network with over 850 miles of pipe ranging from 2 inch distribution pipe to 72 inch transmission mains consisting of 15 different pipe materials. AWWU currently has over 85 miles of water transmission mains, which are those pipelines larger than 24-inches in diameter. These mains have periodically been installed over the years since 1965 with the average age of the transmission mains being 22 years. Most of these pipes have not been inspected since it was first installed and its condition is unknown. Through its asset management program, AWWU categorized its transmission mains into risk categories based upon the probability and consequence of their failure. These risk categorizations were based upon limited data and as table top exercise. Like many utilities across the country and around the world, AWWU is trying to become more proactive and less reactive in its maintenance of its critical assets. To be in a position to plan ahead, AWWU realized the need for additional data on the condition of its transmission mains. Within its limited project budget, AWWU performed condition assessment of all "Major" risk pipe and as much of the "Moderate" risk pipe that it could. With the limited budget, approximately 12 miles of major risk pipe and approximately 13 miles of minor risk pipe were able to be inspected. Using a combination of SmartBall, PWA, electromagnetic, and visual inspection technologies, field work for this project was conducted in September and October 2011. Because of AWWU's system configuration, access limitations, traffic impact concerns and other factors, the condition assessment was broken up into three segments. The largest of which was 91,000 feet in length and crossed multiple pressure zones. The preparation for these inspections and the subsequent support needed during the inspections was no small feat. To keep the ball moving, AWWU had to model its system under certain operating criteria to make sure we could move the SmartBall from its insertion point all the way to its extraction point within a 12 hour period of time that data could be recorded. The water transmission system had to be setup to direct flow by closing of a number of mainline and secondary valves, draining reservoirs, altering hydraulic grade lines, and allowing for the by-pass of key facilities such as PRVs. This paper discusses the logistical and coordination efforts required as well as the necessity to make changes to the distribution system in order to perform the condition assessments. The paper also discusses the following topics:AWWU Asset Management Planning;Background of Project;Selection of Condition Assessment Technologies for this project;Presentation of findings from the work, andKnowledge Gained.