Condition Assessment of a Wood Stave Intake, a Hand Dug Tunnel, and Concrete Cylinder Pipelines

The City of Bellingham, WA currently operates a water supply system that was constructed in 1939 to take raw water from Lake Whatcom and convey it to the City’s 24 MGD drinking water treatment plant. The system has reliably served the City over that time, but is in need of key repairs to maintain the assets and extend their useful service life. Making those repairs will be challenging given the age of the infrastructure and the level of system redundancy originally designed. A thorough condition assessment was an important part of the City’s approach to characterize the assets, identify the key repairs needed, and prioritize them against available budget and resources. The 5-mile intake system consists of: 66-inch wood stave intake pipe, 78-inch hand dug tunnel, and 48-inch/68-inch concrete cylinder supply pipelines. Underwater laser profiling, commercial diving inspection, topside corrosion studies, and deep tunnel man entry were used to evaluate the condition of the existing assets and identify critical repair and replacement needs. This paper will include an overview of the approach, existing components, data gathered, and study conclusions.