Go East Landfill Closure and Alpine Estates Subdivision

In 2009, private investors P&GE, LLC purchased the Go East Landfill property, a contaminated and long-abandoned landfill. The landfill was allowed to accept “wood, mineral, and concrete solid materials,” but eventually also accepted other waste, including metal dust (magnesium, phosphate, and aluminum) in 1974. This waste later caught fire, resulting in aboveground and underground fires due to oxidation of the metal dusts. The fires were put out, and the landfill was abandoned in 1986. P&GE, LLC intended to complete environmental cleanup and closure of the site to sell to a developer. P&GE utilized PACE Engineering as the engineer of record for the landfill closure.

GeoEngineers contributed critical geotechnical and environmental services as a member of the PACE-led project team, helping to design the landfill cover system and to consolidate, re-grade, and close the landfill. GeoEngineers guided the project through Washington’s Model Toxics Control Act (MTCA) cleanup process and contributed to a landfill closure design that met Ecology’s requirements while reducing construction costs. Following the cleanup and closure, a 96-unit subdivision and neighborhood park were built around the perimeter of the capped Landfill. The project is a highly-visible example of how civil engineering, geotechnical engineering, and environmental cleanup can work together to develop abandoned and risky properties and turn them into assets that benefit the owner, developer, and public.

Approach

• Consolidation of 60,000 cubic yards of landfill debris from 9.5 acres to a 6.5-acre footprint.
• Design and installation of a geosynthetic cover system consisting of a 40-mil double-sided textured LLDPE geomembrane overlain by a geocomposite geonet and two feet of cover soil to isolate contaminated material.
• Implementation of Deep Dynamic Compaction (DDC) beneath the stormwater detention pond to help consolidate landfill material, reducing long-term settlement risks, project costs, and time expenditures.
• Navigation of complex permitting requirements under MTCA and local regulations.
• Provision of full-time environmental oversight to manage excavation and disposal of hazardous materials, including 250 tons of asbestos-containing debris.
• Mitigation of health risks for residents and minimization of environmental disruption.
• Preservation of less-impacted areas of the site, such as a slope on the northeast side of the property.
• Provision of full-time geotechnical monitoring and testing during construction, which included geomembrane installation and seam welding of the landfill cover system, monitoring of geosynthetic construction and cover soil placement.

Results

• By balancing environmental requirements with cost efficiency, GeoEngineers achieved a landfill closure that met strict regulatory standards while still supporting the client’s objectives.
• GeoEngineers helped transform this brownfield into Alpine Estates, a 96-unit residential development with a play area and other amenities located over the closed landfill.
• The project’s success underscores how professional consultants, environmental agencies, and investors can work together to create safer communities.