DESCRIPTION
The restoration project is located at River Mile 2 of the Duwamish Waterway at the site of the former Seaboard Lumber Mill which operated from around 1929 until the early 1980's. The site is in the vicinity of Kellogg Island and on the last remaining oxbow of the Duwamish River system. The site contains 5.7 acres of upland and 10 acres of tidelands. Historically, the upland site was a marsh/channel of the Duwamish River. Developed as an industrial site, the area was filled with waste-bearing fill material consisting of silt, sand, and gravel mixtures with broken asphalt, rock, concrete, brick, wood and metal debris. Investigations revealed soils with concentrations of TPH, lead, mercury, and polycyclic aromatic hydrocarbons (PAHs) that exceeded Washington State Model Toxics Control Act cleanup criteria. This summary was taken from the NOAA Northwest Region website (http://www.darrp.noaa.gov/northwest/elliott/seabd.html).
The site has been restored but needs improvement to function as originally intended. This would be adaptive management of an older restoration project. This project would expand channel opening width, remove shoreline armor and consider a bridge over the channel for recreational access. Fish do not use restored habitat much.
This restoration site is in one of the last oxbows remaining from the original Duwamish River. In 1999, construction of a protective outer berm occurred, armoring and modifying the shoreline. The armor layer consists of 8-9" quarry stone with voids filled with fish rock (fine/medium gravel and course sand to 3/8"). Parts of the berm serve to completely contain low-level industrial contaminants.
Project construction was completed in 2000 and consisted of several primary activities:
- Demolition of former structures associated with the mill operation; removal of a 9,200 square feet shoreline dock structure including 248 creosoted wooden supporting piles, concrete foundations, areas of paving, and partially buried railroad spurs.
- Removal and disposal of highly contaminated upland soil.
- Containment of low level TPH-contaminated soil by covering with a minimum of two feet of clean soil and erosion control features to ensure containment.
- Excavation of a 1.8-acre intertidal bay designed with a curvilinear edge to elevations between +6 to +12 feet MLLW, protected by two armored spits forming a mouth opening to the Duwamish River.
- The shoreline armoring protects the opening which is designed to provide a balance between creating low flooding and ebbing velocities through the hydraulic connection and preventing low dissolved oxygen and the potential for fish stranding within the site. See design map.
- An amended on-site soil mixture of silts and clays with a high organic content was distributed to a depth of 18 inches over the basin. Planting the slopes of the intertidal area with emergent marsh plants at various elevations, and the introduction of transitional scrub/shrub habitat between the intertidal marsh, upland meadow and forested habitat.
- Intertidal habitat success monitoring will be conducted through 2015.
This information was taken from the NOAA Northwest Region DARRP website (http://www.darrp.noaa.gov/northwest/elliott/seabd.html).
Duwamish Tier 1
