Bothell City Council awarded the second phase of Bothell Crossroads to Hos Brothers Construction in July 2010. The work involved site clearing, stockpiling of preload material and contaminated soil cleanup conducted between mid-August and December 2010. Approximately 23,000 tons of petroleum-contaminated soils were removed (7,200 tons more than originally estimated).
“Preloading” on the west end of the project site was placed to stabilize liquifiable soils that are present near NE 180th Street. These areas have underlying peat deposits that cause the ground to be weak and unstable. The preloading ensured that there will be a solid foundation for construction of the new roadway. The process involved compressing the liquifiable soils by placing a large weight over the unstable area (the fifteen-foot mound of gravel weighing approximately 40,000 tons) over a given period of time to allow for up to 1 and 4 feet of settlement.
The project commenced on August 16, 2010 and was physically completed on December 6, 2010 for a final project cost of $2,094,747. The costs were split between the Bothell Crossroads project ($959,699) and the Downtown Contaminated Soil and Groundwater Cleanup project ($1,135,048).