Location: Port Hadlock, Washington
Client: Washington Department of Ecology
Contract Value: $2,988,699
This site was a former iron and steel mill located in Port Hadlock, WA. Past mill operations resulted in contaminated soil, sediment, and groundwater and left a large amount of slag and other buried debris. The site is located on property owned by Jefferson County and is currently used as a public park space but the cleanup action was conducted by Ecology under Model Toxics Control Cleanup Act (MTCA) regulations.
AEC, as the lowest responsive bidder, was contracted by Ecology to perform intertidal excavation of 6,300 cubic yards of contaminated near-shore sediment and 5,600 cubic yards of upland soil to a depth of 12 ft. We also performed subsequent transportation and disposal of contaminated soil off site.
The site was organized into three separate excavation areas:
- A small excavation at the south end of the site below the existing ordinary high water mark (OHW) requiring excavation and handling of water on tidal cycles.
- An Intertidal excavation from within a sheetpile shoring system also below OHW.
- A dry excavation just upland of the shoring system to a depth of approximately 3 feet.
In an effort to reach the extent of contamination in the tidally influenced area, the Design Engineer specified the use of a steel sheetpile shoring system to keep water out of the work area. AEC was asked to work closely with a shoring subcontractor to design the shoring system which called for large steel sheets to be driven directly into exposed sediment using a vibratory hammer. However, during the design phase, AEC proposed an alternate method of using a Portadam steel cofferdam system that would allow us the ability to “contain in” all of the remedial excavation areas and control bay water from entering the remedial excavation area. The Portadam system is comprised of welded rectangular steel “A” frames and a tailored vinyl liner membrane suspended from the frames which drapes along the “A” frame & bed providing a watertight barrier.
The use of the Portadam system instead of sheetpile was beneficial in that excavation areas below elevation zero that require groundwater handling were “contained in” and restricted from above surface tidal water influence, we would be able to more easily handle and treat any groundwater that did enter the work area, it gave us the ability to easily extend the excavation both horizontally and vertically if necessary, and the system’s flexibility and ease of use would ensure project completion within the fish window. Ultimately, the Design Engineer and Ecology agreed that our proposed alternate was superior, safer, environmentally-beneficial and would substantially limit the potential for our work area to become inundated with bay water.
The Portadam system worked perfectly and AEC was able to reach the entire extent of contamination with substantially less water management/dewatering. Upon completion of the remedial excavation, all areas were graded and backfilled and AEC installed an upland multi-component environmental cap, consisting of specialized geo membrane materials and a total of approximately 19,000 cubic yards of clean soil capping material. Lastly we performed final planting and revegetation of disturbed areas.