Tapani’s $28-million-dollar contract included the construction and commission of two run-of-the-creek hydroelectric projects for Snohomish County PUD No. 1. One project was located on Hancock Creek and the other on Calligan Creek, both in unincorporated King County, approximately nine miles northeast of North Bend, Wash. Each facility consisted of a concrete dam with 30-foot-tall cut-off walls and complex intake structures to divert flow to the hydro-generator. When operating at full capacity, each project will generate six megawatts, which is enough to power 12,000 homes.
Between the two sites, the work consisted of more than 250,000 cubic yards of excavation to allow for the installation of nearly 14,000 linear feet of 39-, 41-, and 45-inch penstock piping down the rugged mountainous terrain to the powerhouses.
Tapani built two concrete powerhouses to enclose the generation equipment and the water discharge passage. Each powerhouse had a complex concrete structure to divert flow to the hydro-generator while still maintaining flow in the creek for fish life. Tapani’s employees self-performed the installation of the complex hydro generation equipment that came from Europe, which had to be installed with tolerances within four-thousandths of an inch.
A major unforeseen excavating challenge was discovering that the depth of the Kame Terrace was actually 28 feet rather than 14 feet as initially understood. This was discovered in the middle of a very tight in-water work window, but crews still met the deadline and kept the cost to a minimum for the client. This was a direct result of a team effort between Tapani, Snohomish County PUD staff, and their design team. Challenges for this project were mostly due to the remote and rugged project location. Tapani crews worked for two years on this project through extreme high-elevation weather, stayed on schedule, and worked through many challenges to construct a quality form of renewable energy.