Knox County Landfill Leachate System Modifications

Background

Knox County Landfill 3 was designed in the early 1990s during the transition to Subtitle D landfill regulations. The initial leachate collection system relied on gravity drainage to a single loadout point located nearly a mile from the main operations, at the farthest point from the site entrance. After a decade of operation, a small storage area with a portable pump was installed to fill tanker trucks to facilitate leachate transport to a publicly owned treatment works (POTW). However, the tankers could only be filled during warmer months due to pump and access road limitations, prompting the County to seek a more efficient, long-term solution for leachate management.

Approach

The project involved a comprehensive upgrade to the leachate collection system, including the installation of a new lift station with a single-phase pump, approximately one mile of dual-contained forcemain piping, two 30,000-gallon dual-wall underground storage tanks, and a truck loadout pumping system. The forcemain design incorporated four cleanout manholes with leak detection and air release valves to maintain flow efficiency across the site’s varied topography and long distance. To maximize construction efficiency and plan for future gas collection, a gas header pipe was installed in the same trench. The new loadout station was strategically placed near the site entrance and operations hub–the location of the future landfill gas flare–significantly reducing internal haul distances. Additionally, the system was designed to accommodate future leachate volumes from Landfill 4, minimizing the need for redundant infrastructure. The design team also overcame the challenge of limited power availability at the remote site by selecting a single-phase pump capable of operating reliably in all weather conditions.

Results

The upgraded leachate management system delivered immediate and long-term benefits for Knox County. By relocating the loadout station and enabling year-round operation, the County can now haul an additional 6,000 gallons of leachate per day using the same staff and equipment. The system’s all-weather capability effectively doubles the operational window for leachate removal, increasing overall capacity and reducing environmental risk. As leachate volumes from Landfill 3 decline and those from future Landfill 4 increase, the shared system will allow for continued efficiency without duplicating storage costs. This solution addressed both current operational challenges and future growth, providing Knox County with a sustainable, cost-effective leachate management strategy.