The Upper Northwest Interceptor 1&2 project included 19, 240 feet of 144-inch-inside-diameter pipe using earth pressure balance tunneling methods; 130 feet of 120-inch-diameter interceptor pipeline; 23 access manholes spaced approximately 1,000 feet apart along the alignment; an 84-inch by 144- inch transition structure; a 144-inch by 120-inch transition structure; and connection of three existing sanitary sewer lines to the interceptor using guided boring machine methods.
The site included mixed face geology of soft soils, clay, and rock ranged from highly weathered to slightly weathered granite, coarse sand, and silt at pressures up to four bar. Precast segmental liners molded with PVC sheets were installed to protect the concrete from degradation due to corrosive sewer gases. The first of its kind in North America, they were manufactured by Traylor Shea Precast. Boring was completed two months ahead of schedule.