Beneficial Reuse of Dredge Spoils from Squalicum Harbor
(Bellingham, WA) The Port of Bellingham manages Squalicum Harbor, a 1,400 slip marina on the northern shores of Bellingham Bay in Washington State. Improvements to Squalicum Harbor’s Gate 3 include the replacement of Docks F and G, and maintenance dredging of approximately 40,000 cubic yards of sediment to increase the depth around the F and G mooring area, two harbor entrances, and a main channel. Landau Associates evaluated the sediment quality and provided dredged material characterization services to support the evaluation of various disposal options for the dredge spoils that included:
- Open water disposal in Puget Sound through the US Army Corps of Engineers Dredged Material Management Program (DMMP).
- Use as upland fill material.
- Beneficial reuse to replenish the nearby marine habitat bench.
- Beneficial reuse as a component of a future capping system at the Cornwall Avenue Landfill, a former solid waste landfill located on the Bellingham waterfront. The Cornwall Avenue Landfill was closed in 1965, but the shoreline erosion protection used for closure was inadequate; landfill materials have been eroding into Bellingham Bay over the intervening years. Landau Associates is conducting a remedial investigation/feasibility study (RI/FS) of the Cornwall Avenue Landfill on behalf of the Port of Bellingham, City of Bellingham, and Washington State Department of Natural Resources.
The selected disposal option, beneficial reuse at the Cornwall Avenue Landfill, involved layering about 47,000 cubic yards of material dredged from Squalicum Marina on an upland portion of the Cornwall Avenue Landfill site. The purpose of the interim action was to reduce the amount of rainwater that soaks into the ground, in turn reducing the amount of water flowing through buried municipal waste and picking up contaminants as it enters Bellingham Bay.
Washington State Department of Ecology approved the Port’s request to use the stabilized dredge spoils as low permeability fill material at the Cornwall Avenue Landfill site.
Dredged materials were barged from Squalicum Harbor to the former Georgia Pacific mill site (a nearby Port property), stabilized to remove excess moisture, and then trucked to the Cornwall Avenue Landfill site. Sediment stabilization was accomplished by offloading of the material from the barge into initial dewatering containment areas, blending the material with Portland Cement using a pug mill batch plant system, and allowing time for the material to achieve a soil-like consistency.
Environmental control measures at the sediment processing site included use of paved surfaces, lined concrete block storage cells, and sump pumps. Stormwater and free water draining from the dredged material was routed to the site’s existing stormwater pump station and pumped to the existing aerated stabilization basin treatment lagoon, previously used to treat wastewater and stormwater from the former mill site.
Environmental control measures at the landfill site included berm construction along the shoreline, installation of a landfill gas control system, construction of lined roadways and drainage ditches, and installation of a geomembrane cover over the stabilized sediment to prevent contact with stormwater and limit stormwater infiltration through the underlying landfill refuse.
Future plans for the Cornwall Avenue Landfill site include final grading of the stabilized sediment, construction of the final cover system, and redevelopment of the site into a park, trail, and mixed use area.
This project was awarded an Engineering Excellence Silver Award (Originality-Innovation) from the American Council of Engineering Companies (ACEC)–Washington.