Case Study: Dewatering Plan for Transit Maintenance Facility

Client: Sound Transit (under subcontract to Clearcreek Contractors) Location: King County (Seattle), WA Contact for geotechnical projects: John Peterson

Project Background & Challenges

Before Sound Transit could build a maintenance facility on this 1.4-acre site, petroleum-impacted soils needed to be excavated. The construction specifications called for dewatering to allow the removal of impacted soils; they also required placing a geomembrane liner at the base of the excavation and then backfilling. The site was underlain by variable fill, which included landfill waste; no hydraulic information was available for these materials, nor was the extent of contaminated soils defined. These unknowns posed a significant challenge to designing an effective, implementable dewatering system.

Solution

Aspect’s dewatering plan focused on maximum flexibility for adjusting to uncertain field conditions during construction. The plan specified the use of rugged, portable steel sumps that could be installed and moved easily by the excavator, allowing crews to adapt to variable conditions during construction. Soils were removed on schedule and within budget.