The Island of Tinian has 3,500 residents and generates approximately 2,623 tons per year of mixed refuse from residential, commercial, institutional, and industrial establishments. Historically, solid waste was placed on an unpermitted dump site within the 10,000-foot restriction of the West Tinian Airport. The old disposal site operated as an open burn dump.

In 2010 the Commonwealth of the Northern Mariana Islands selected Tetra Tech to design a new U.S. Environmental Protection Agency (EPA) American Recovery and Reinvestment Act-compliant sanitary landfill to meet Tinian’s waste disposal needs. The client has selected in the northwest portion of Tinian as the site for the new landfill project, financed by the U.S. Department of the Interior, Office of Insular Affairs.

Tetra Tech conducted geotechnical and hydrogeologic investigations, developed conceptual and final designs for all landfill features, and provided construction engineers’ cost estimates, which are adequate for financial appraisal, including a cash flow projection of future operating costs.

Specific site features include the following:

  • All-weather main entrance and perimeter road
  • Shared-scale house and administration building
  • 6,700-square-foot, single-story equipment maintenance building
  • Diversion facility incorporating storage areas for green waste and white goods
  • Site power distribution and lighting system
  • Construction plans for fire suppression and domestic water supply system
  • On-site septic system or evapotranspiration bed
  • Clearing, grubbing, and grading plans
  • Hydrology study and surface water management plan
  • Construction drawings for installing the liner system in compliance with EPA requirements
  • Phased liner system construction plans
  • Leachate collection and treatment system design
  • Landfill gas management plans
  • Landfill final closure design documents, including a conceptual final grading plan and associated surface water control plans
  • Slope stability analyses for the final cover configuration in compliance with EPA requirements
  • Visual screening features

Tinian receives approximately 81 inches of rainfall per year, so leachate and surface water management are key design considerations. A low-maintenance, gravity-drain system is under development to minimize leachate generation. The system will take advantage of the site’s natural contours and minimize the need for mechanical conveyance mechanisms. Surface water management is another key design feature.

Tetra Tech designed drainage improvements to divert surface water away from disposal areas, and control surface water run-on and runoff. All site improvements were designed to withstand typhoon conditions.