SR 520 - Natural Resource and Parks Mitigation

Aquatic mitigation site Park resources Wetland mitigation site Wetland and aquatic mitigation site

Click the colored icons in the map to find more information on specific SR 520 mitigation projects.

How is WSDOT mitigating for construction impacts of the SR 520 Bridge Replacement and HOV Program?

When planning transportation projects, WSDOT first seeks to avoid or minimize adverse effects to the environment. If a project has unavoidable effects, we must mitigate for them. On the SR 520 Bridge Replacement and HOV Program, we have conducted mitigation projects at numerous sites, primarily in the Lake Washington watershed, to compensate for the program’s impacts. While the majority of our mitigation projects are now complete, a few remain, such as mitigation at the WSDOT Peninsula in Montlake, which will be completed near the end of the SR 520 Program. As SR 520 construction moves forward, WSDOT has made various design refinements that reduce our anticipated impacts on the natural environment. Consequently, we continue coordinating with regional stakeholders to ensure that our environmental mitigation program matches up with our construction impacts. You can find more information about our environmental projects by clicking on the individual sites shown on the map above.

How did WSDOT identify its mitigation projects and locations?

To identify mitigation sites, WSDOT undertook a comprehensive, watershed-based screening process in coordination with local, state and federal regulatory agencies, tribes and other stakeholders. WSDOT restores construction-related impacts that occur on site. We have also conducted as much mitigation work as possible within the boundaries of project construction. On-site mitigation is limited, however, by existing land use, high-density development within the SR 520 corridor, and insufficient mitigation locations in the corridor. So, to meet our environmental commitments, WSDOT also conducted substantial environmental mitigation at off-site locations.

In most cases, specific mitigation projects have been implemented by WSDOT and our mitigation partners. In other instances, WSDOT contributed to King County’s Mitigation Reserves Program in lieu of conducting or sponsoring a site-specific project. This in-lieu option provides fund contributors like WSDOT the ability to pool resources and fund mitigation projects that can yield greater environmental benefits and might otherwise have insufficient funding. Participating in an in-lieu fee program is the preferred approach by our state and federal regulatory agencies. Additional information on the natural resources mitigation planning process and proposed wetland and aquatic mitigation sites can be found in the wetland mitigation plan (pdf 18.7 mb) and Aquatic Mitigation Plan (pdf 5.6 mb).