Comprehensive Solid Waste Engineering Services for Cowlitz County

Client: Cowlitz County

Location: Longview, Washington

MFA provides comprehensive solid waste engineering services for Cowlitz County, assisting the county in the cost-effective management of their solid waste system and the associated environmental obligations.

Completed projects include:

  • Design and construction support for development and closure of landfill cells, including the liner system, the cover system, landfill gas modifications, and stormwater controls
  • Design and construction support for truck scales and the associated payment system
  • Due diligence for the acquisition of the Headquarters Landfill
  • Preparation of the county’s Solid Waste Management Plan
  • Maintenance of various landfill-operations-related plans
  • Stormwater permit assistance
  • Alternative-daily-cover permitting assistance
  • Photogrammetry of the condition of the Headquarters Landfill, using MFA’s unmanned aerial systems services

Additionally, MFA prepared the Tennant Way Landfill Post-Closure Plan and the Facility Use Assessment. These documents provide a detailed summary of the conditions and obligations at the landfill and will support clear communication should a development opportunity arise—a critical resource for county managers.

Tennant Way Landfill Closure Design and Construction Oversight

One of the highlights of our engineering services was the closure design and construction oversight for the Tennant Way Landfill. Upon reaching its permitted fill capacity, the landfill site in Cowlitz County required closure per state and local health jurisdiction requirements. Landfill closures require thorough knowledge of Department of Ecology closure requirements; the MFA project team had the understanding of the process needed for design and oversight of the closure in collaboration with the county and various contractors.


  • The landfill site was stabilized with minimal environmental impacts and no adverse impact to the public waterways.
  • MFA designed a final landfill cover that employs an alternative cover approach (a geosynthetic clay liner), which resulted in more available disposal volume, approximately $1 million in savings on material and construction quality assurance testing costs, and a shortened construction schedule. The use of an alternative cover alleviated the need for a 2-foot-thick soil cap, allowing the county to maximize the amount of waste that could be held prior to closure.
  • With the development of the post-closure documents, including the Facility Use Assessment, the county has a clear path forward for maintaining the closed landfill and maximizing the ability to safely repurpose portions of the site as a benefit to the community.
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Cem Gokcora, PE

Senior Engineer

(971) 713-3573