Terracon was contracted to provide geotechnical services to assess site conditions at the North Twin Bridge in Des Moines, Wash. The bridge was built in 1950 and is about 230 feet long, spanning a steep sided ravine above McSorley Creek. During initial observations of the site, a void was discovered below the foundation of Bent 1. Terracon evaluated the existing foundation support conditions at Bent 1 and provided recommendations for methods for emergency foundation repair. Additionally, Terracon also provided options for seismic retrofit intended to upgrade the bridge to a performance based seismic retrofit Category D.