In-Water Construction Begins at Sediment Cleanup
Portland, Oregon. July 8 – With federal and state permits in hand, Zidell is moving their cleanup activities into the Willamette River in the South Waterfront neighborhood of Portland, Oregon. The issuance of the Clean Water Act (CWA) Section 404 Dredge/Fill Permit by the U.S. Army Corps of Engineers allows Zidell to start sediment cap construction in what will be a complex, four-month construction sequence. The sediment cleanup is a major step toward redevelopment of the property, and is one of the first to be conducted in the lower Willamette River.
The permitting process led by Maul Foster & Alongi, Inc. (MFA) and Zidell’s project manager, Paul Fishman, required more than 18 months of innovative design and negotiation. The Section 404 permit included an Endangered Species Act consultation with the National Marine Fisheries Service, and a DEQ-issued CWA Section 401 Water Quality Certification. These permits ensure that the project will not harm protected salmon species.
MFA engineers and scientists have been the design lead for the Bank and Sediment Remedial Action, on a design team that includes GeoDesign, Watershed Science and Engineering (WSE), and SWCA. The remedial action is a capstone to the site investigation, risk evaluation, and feasibility study process that Zidell and MFA initiated in 1998. The sediment cap design will safely isolate contaminants in a 13-acre area from fish and other organisms that live in the Willamette River and the river bottom sediment. The remedial action also removes hot spots of contamination in the bank, as well as asbestos, steel, and other debris from decades of industrial activities at the site.
The sediment cap consists of clean river sand armored with rock armor, and topped with fish habitat gravel. MFA scientists worked with nationally recognized sediment cap experts to develop a contaminant transport model to demonstrate that the sediment cap will effectively isolate contaminants. Working with GeoDesign and WSE, MFA engineers also demonstrated that rock armoring will protect the cap from boat traffic and during extreme flood events.
The design includes a newly constructed section of riverbank where a bioengineered system, using native plants with significant root systems, will armor the bank and protect the bank soil from river scour. Replacing traditional rock armoring with the bioengineered protection significantly reduced the habitat impacts of the project.
July 1 represented the start of a very busy and complex four-month in-water construction cycle. The work will include removal of over 2,000 old dock piles, bank stabilization of over 3,000 feet of prime riverbank property, capping 3 acres of upland greenway, and placement of 13 acres of sediment cap. In-water construction will require three crane derricks and multiple materials barges in addition to more traditional land-based equipment performing excavation and bank capping work. MFA will provide engineering oversight of the construction activities.
Work has been closely coordinated with the construction of Portland’s newest light rail bridge, which will cross Zidell’s property and the sediment cap. Two additional crane derricks and up to five supply barges will be used to construct a temporary work bridge and coffer dam immediately outside of the Zidell sediment cap.
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