Protecting Steel Poles and the Environment! SR529 Mitigation—A Case Study on Environmental Factors and Steel Structure Preservation

As utility professionals we are responsible for infrastructure spanning all over the country through a myriad of environmental and ecological challenges. We know the importance of being good stewards of the environment while also balancing the need for progress and development. Regardless of your operating territory, on some level, all engineering and O&M teams have needed to coordinate with other agencies to mitigate damage or disturbance of the environment while maintaining existing or constructing new transmission lines. And in some instances, we are forced to respond to situations born out of factors that were out of our control entirely. The SR529 Mitigation Project is a wonderful example of multiple agencies responding to a need with some “out of the box” thinking. In 2018, the Washington Department of Transportation (WSDOT) notified Snohomish County Public Utility District (SNOPUD) of their intention to create a new estuary along the Snohomish River that would reclaim damaged wetland from years of transportation, residential, and commercial development, as well as offset the future destruction of ecologically sensitive areas from subsequent highway expansion projects. The estuary would be critical for declining salmon populations and other connected species in the area. The issue for SNOPUD was that the proposed estuary happened to encompass the right of way for a major transmission line serving the region. Once flooded, SNOPUD would have no way to access and maintain a major river crossing structure for that line. It also meant that the foundation and base section of the galvanized tubular steel tower would be subject to high salinity tidal flows that would regularly submerge those structurally critical components. Of course, the tower was not designed or installed with this kind of exposure in mind. SNOPUD had a decision to make. They could either move the line out of the intended flood zone or upgrade the affected crossing structure to withstand these new environmental conditions, knowing that once WSDOT completed their project, the only way to access this tower would be via inland barge (a costly endeavor). Complicating this decision further was the aggressive timeline that WSDOT outlined for having all utility work completed before they intended to breach the dike of the main river. This paper outlines the technical challenges and decision-making process that SNOPUD endured as well as the corrosion mitigation and structural upgrade efforts that were undertaken to extend the life of the transmission tower in its new environment.