Terminal Site Cleanup Action

As part of preparation for the redevelopment of this terminal site, our client required cleanup and remediation under Ecology’s Voluntary Cleanup Program. The property, which is located along the industrial waterfront of Salmon Bay in Seattle, is approximately 11 acres in size and previously existed for bulk fuel operations in the 1940s to support World War II efforts. The site supported large quantities of fuel being stored and distributed during and after the war. These operations resulted in releases of petroleum hydrocarbons, chlorinated solvents, wood preservative, and metals into soil and groundwater on and around the site.

Forgen was selected to perform in situ solidification and stabilization to address source area soil with indicator hazardous substances and light nonaqueous phase liquids (LNAPL) removal. There were six individual excavations between the bulk terminal and the waterfront property with unique depths and complexities. Our team both constructed and installed an interceptor trench to capture and treat groundwater containing indicator hazardous substances which included a gravity well, treatment vault, and permeable reactive barrier comprised of a ZVI/sand blend. The scope also included installation of two solider pile shoring walls and an earthen retention system to facilitate excavation against sensitive structures. Surface asphalt (700 tons were expected and 1,700 tons were disposed) and concrete covering multiple excavation areas was also removed. Our team was presented with a unique challenge when the depth of ISS was at the maximum limit for bucket mixing; this caused equipment downtime for repairs and maintenance. Our team adjusted their approach by excavating to depth, stockpiling material adjacent to the mixing cell, and mixing material into slurry.

Further challenges on this project included the depth of mixing required to stabilize the contaminants of concern and proximity of the adjacent city street and railroad required two earth retention shoring systems and an excavator with the capacity to bucket mix greater than 25’ in depth. In addition, the allowable depth of the shoring system adjacent to the right of way for the railroad, required Forgen to implement a specific mixing sequence to prevent movement of the soldier pile shoring system.

This project was completed successfully, leaving the site appropriately cleaned up and thereby allowing redevelopment to occur.