- Environmental Remediation
City of Yakima
2018 – 2021
- Project presentation at American Public Works Association 2021 fall
Piper Roelen, PE, CHMM
Yakima Landfill Interim Action Design and Construction Support
Terrace Heights is the fastest growing neighborhood in the City of Yakima, but only one bridge spans the Yakima River to connect it to I-82 and central Yakima. The City, in cooperation with Yakima County, the Washington State Department of Transportation (WSDOT), and the Federal Highway Administration (FHWA) is planning a major infrastructure project to connect Yakima and Terrace Heights. This project will create the access and infrastructure needed for redevelopment of more than 200 acres of under-utilized and unmarketable land while providing enhanced connectivity to interstate commerce. The project will ultimately include the bridge over the Yakima River, an interchange with I-82, an underpass beneath I-82, a railroad crossing, and the associated roadway system in Yakima and Terrace Heights. The logical terminus for the project in Yakima includes a roadway through a former unpermitted municipal solid waste (MSW) landfill and former Boise Cascade mill site that are formal cleanup sites under the purview of the Washington State Department of Ecology (Ecology). The roadway project represents a significant opportunity for economic stimulation to the region.
The City has leveraged multiple funding sources to keep the project moving forward including the Local Infrastructure Finance Tool (LIFT) program, the Connecting Washington Transportation Package, and Ecology Remedial Action grant funds.
For Ecology to allow the roadway project to proceed through the former landfill and mill sites, the City was required to integrate roadway design and construction with Model Toxics Control Act (MTCA)-compliant plans and implementation of interim cleanup activities. The construction plans also had to consider unique challenges resulting from crossing the former MSW landfill site including management of solid (and potential hazardous) wastes; health and safety considerations from ongoing landfill gas (LFG) generation; and management of potentially impacted water from dewatering activities and construction stormwater management.
Based on the findings from a supplemental remedial investigation, additional pre-design investigation activities, evaluation of geotechnical considerations, and review of preliminary roadway and infrastructure designs, Landau prepared an interim action work plan that included:
- Specifications for MSW and mill site wood debris excavation, management, and disposal within the City right-of-way (ROW) and roadway prism;
- Designs for a low-permeability soil wall to be constructed along the ROW boundary and integrated with excavation backfilling to mitigate and minimize LFG migration into the ROW and into proposed and future utility corridors;
- Specifications for plastic liners to be placed over the MSW excavation faces for dust and odor control and additional mitigation of LFG migration into the ROW;
- Specifications for management of water from dewatering activities and construction stormwater;
- Recommendations for construction scheduling during non-irrigation (low groundwater table) season to minimize excavation of MSW below the groundwater table or the need for dewatering and associated water management and disposal; and
- An Excavated Materials Management Plan for use by the Contractor and the Yakima County construction oversight team detailing how to evaluate the excavated MSW for indications of contamination requiring remediation or identification of landfill materials that may require handling and disposal as a hazardous waste, special waste, or otherwise requiring special management.
Landau prepared the interim action work plan and designs and specifications in 2018–2019 in conjunction with the City’s civil design consultant. The City received Ecology approval in 2020. The integration of the roadway construction with the interim action also provided the City with the opportunity to receive grant funding from Ecology.
Roadway/interim action construction was completed between November 2020 and June 2021, with Landau providing as-needed consulting and oversight of a remedial excavation of previously unknown soil contaminated with petroleum beneath the MSW, and management of perched groundwater in the MSW with petroleum sheen.
The MSW removal and disposal, excavation backfilling, and LFG mitigation barrier wall construction project was completed during the low-water table season preventing the need for any excavation dewatering.
Completion of the interim action cleanup and environmental protection activities will allow the City of Yakima to complete the roadway project with minimal environmental hurdles.