Original contract amount
$19,879,913

Address
North King County

Start of construction
March 2000

Expected completion date
September 2001

Tolt 2 will carry potable water to the city of Seattle and the many cities and water districts that purchase water from Seattle. Tolt 2 is intended to provide enhanced dependability to the water conveyance system by providing redundancy and a means for allowing dewatering and inspection of the existing Tolt Pipeline No. 1 (Tolt 1).

Presently, water is conveyed in Tolt 1, a 54- to 60-inch-diameter concrete cylinder pipeline placed in service in 1964. Tolt 1 extends from the South Fork Reservoir east of Duvall to the Lake Forest Park Reservoir. Tolt 2 will occupy the same right-of-way as Tolt 1. The right-of-way is a cleared corridor 55 to 100 feet wide, planned to accommodate the second pipeline. Tolt 1 occupies the north side of the right-of-way and Tolt 2 generally will occupy the south side. Electrical transmission/distribution lines are located on much of the corridor as well. Tolt 2 will be a buried steel pipe similar in size to Tolt 1.

The construction techniques will vary along the route. Cut and cover methods will be used for most of the pipeline installation. Special crossing methods are required at several locations:

• top of Norway Hill (bore and jack), Sammamish River (microtunnel)
• SR-522/Bothell Way (bore and jack), 96th Avenue/Waynita Way (inside of an existing casing pipe)
• Swamp Creek (bore and jack beneath the two forks of Swamp Creek and a pile-supported section through a peat zone)
• Cranberry Swamp (pile-supported section through a peat zone)
• 61st Avenue Northeast (bore and jack).