Trains to Mains: How to Relocate Three Kilometers of Water Main in Preparation for Light Rail in Downtown Tacoma, WA

The regional transportation authority, Sound Transit, is in the process of constructing light rail transit expansion to its Tacoma Link service. The existing 2.5 kilometer light rail line serves six stations and over a million riders; the expansion will add four kilometers of light rail line and six new stations. The proposed project is within the city of Tacoma's existing urban corridor, which consists of high-density urban development, and high-traffic-volume streets. Construction is anticipated to start in 2018, with commissioning of the new rail service in 2022. As part of the project, approximately three kilometers of 6 to 12-inch water main servicing 160 customers including two large regional hospitals will be relocated. This paper will go over the techniques and design approach used to relocate the water main and will provide details on water main criteria to mitigate light rail stray currents and space constraints, utility conflict resolution through cross-disciplinary design reviews, and methods for maintaining water service during construction.