Seattle Public Utilities

Seattle Public Utilities (SPU) is a large water and wastewater utility with 1900 miles of water mains serving 1.5 million people each day.  They enjoy a respectable 5% water loss rate and see about 200 water main breaks each year.  Several years ago the PE Alliance was contacted by SPU engineers and asked to give a seminar. One of their engineers had moved from the Bay Area where HDPE was popular and he wanted to expose his engineering colleagues at SPU to HDPE pipe.  So we conducted the 2016 seminar and were asked to come back and do it again with a different group in 2019. We did not hear much, but the wheels were turning. 

The city then trialed HDPE on a few smaller diameter projects with good success. So the PEA was then invited to train a few of their staff as fusion techs so that the expertise could grow in the system and we did that in 2021. With the assistance of McElroy Manufacturing we left two fusion machines with them to use on projects and for training. Finally , the body of work keeps growing.   In 2022, Isco Industries Drew Mueller assisted the city on a 54” slipline of a failing, critical concrete raw water line in the mountains. The city of Seattle sources 60% of its water from the Tolt Watershed. One of two redundant raw water lines had been abandoned for several years due to failing concrete pipe and concerns about further damage due to seismic events and the liquification of soils in the Cascade foothills. SPU rehabilitated approximately 2,600 lf of the 66-in. diameter concrete pipeline known as Tolt Pipeline No. 1. It traverses an active landslide area that has been moving approximately 1”per year for the last 20 years. HDR performed a detailed condition assessment to determine if sliplining would be feasible to minimize open-cut installations within the slide area.  The pipeline alignment and profile, pipe material design parameters, and slipline pipe pull forces were evaluated to determine the number of pit locations and maximum slipline lengths, resulting in of three slipline segments of a 54” HDPE DR-17 pipe using four launch and retrieval shaft locations. 

Illustration: Tolt image and one from training in 2020