Lake Washington Brownfield

Former Wood-Treating Plant – Renton, WA

CRETE principals led the investigation and project_sports-fields-aerialcleanup of this brownfield redevelopment project at a former wood-treating site on Lake Washington. CRETE principals completed the RI/FS, Cleanup Action Plan, Consent Decree, Engineering Design Report, and design plans and specification for cleanup of the property. Remediation on the property consisted of:

  • In situ soil mixing of source area soil and NAPLs with cement and bentonite
  • Sediment removal from a cove and restoration of a forested wetland
  • Soil capping that was fully integrated with site redevelopment
  • Relocation of a salmon-bearing stream
  • Development of site-wide stormwater management program

In situ soil mixing was implemented because geotechnical constraints at the site made excavation impractical. A cement-bentonite additive was designed to reduce the hydraulic conductivity of the impacted soil, thus restricting contaminant transport to the lake. The additive was also formulated such that the soil-additive mixture exhibited strength similar to that of the native soil. Matching native soil strength allowed flexibility in the use of foundation piles for future site redevelopment. The mixed soil was reused on-site to reduce cleanup costs.

Extensive areas of peat and other organic debris generated methane at the site. Methane mitigation systems were designed and installed in the headquarters building, indoor practice facility, and maintenance building.

CRETE principals managed the sediment remediation and wetland restoration of the cove. A one-acre emergent marsh on Lake Washington was restored to provided resident turtle habitat.

The Engineering Design Report provided adequate flexibility in schedule and cap design scenarios for the final redevelopment design to be regularly adjusted while complying with Washington State Department of Ecology requirements. The capping options included asphalt parking areas, pile-supported structures, football fields constructed of natural and artificial turf, and support areas for maintenance, emergency response, and public viewing.

CRETE principals worked with other design team members to develop a stormwater management system consistent with the 2005 King County Surface Water Design Manual. The design efficiently utilized the limited land space by infiltrating rain water through 18 inches of sand in the football field subgrade, thus satisfying the enhanced treatment requirement for discharge to the lake without using land space for a separate enhanced treatment facility. An integrated pest management plan outlines best management practices for the selection and application of turf amendments to minimize the off-site transport of pesticides and fertilizers. The design also included the use of grassy swales around the parking lot sand filters to satisfy the pretreatment requirement. The stormwater outfalls were also designed to avoid the need for USACE permitting. CRETE principals also provided construction oversight including construction stormwater collection and treatment with carbon dioxide and chitosan prior to discharge to the sanitary sewer.

The final phase of the cleanup action (environmental capping and institutional controls) was completed in 2008 in conjunction with redevelopment activities.

Work Performed

  • Property transaction due diligence
  • Regulatory negotiations – MTCA
  • Upland and sediment RI/FS
  • Permitting – in-water cleanup, wetlands, stream relocation, construction stormwater, Metro discharge
  • Sediment cleanupSeahawksSoilMixingOverview
  • Wetland restoration
  • Shoreline site cleanup and development coordination
  • Methane mitigation systems
  • Construction plans and specifications
  • Construction stormwater treatment
  • Construction oversight
  • Stormwater system design

Value Added

  • Negotiated that RCRA F-waste listings did not apply to soil and groundwater
  • Used physical criteria to minimize the volume of K001 listed waste
  • Negotiated a flexible cleanup schedule to allow coordination with development
  • Created a menu of environmental cap designs to allow multiple site development scenarios
  • Developed the CAP to allow grading and reuse of contaminated soil on site
  • Designed in situ soil mixing of source soil and NAPLs to contain source material due to geotechnical constraints
  • Designed the in situ soil mix to provide a final mix strength similar to that of soil to maximize flexibility in the use of foundation piles for various redevelopment scenarios
  • Integrated enhanced stormwater treatment features, including sand filters and pretreatment, within the environmental caps to maximize the development footprint
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