Filling a Freshwater Lake—Sediment Remediation Considering Net Environmental Benefit for Multiple Stakeholder Goals

Multi-season sediment remedial actions began in June 2017 at Lora Lake, part of a larger Port of Seattle (Port) Model Toxics Control Act (MTCA) Cleanup Site managed by the Washington State Department of Ecology (Ecology) and will be completed in October 2019. The site is located on Port property within the secured area of Seattle-Tacoma International Airport, in a U.S. Army Corps of Engineers (USACE)-managed mitigation area, and within the Federal Emergency Management Agency (FEMA) 100-year floodplain. The site remedy includes placing 56,000 cubic yards of carbon-amended sand cap throughout the 3-acre manmade lake to return it to its native wetland condition. This remedial action was selected through a net environmental benefit approach that considered the goals of multiple agencies and stakeholders. Considerations included compliance with the U.S. Federal Aviation Administration rules for runway protection zones, reduction of aircraft navigation dangers from bird strikes, limitation of disturbance to surrounding USACE-managed mitigation areas, and water quality improvements to downstream Miller Creek, a salmon-bearing stream with local government and community interest. The collaborative remedial design effort included: remedy selection based on consideration of benefits and impacts to the surrounding ecosystem and airport; strategic coordination with local, state, and federal agencies regarding these short- and long-term impacts; and design incorporation of hydrogeologic groundwater flow and engineering floodplain analyses.