Timber Ridge Landfill Closure

Agru America, Inc.

Modern landfills operate under many federal and state regulations. Under the U.S. Environtmental Protection Agency (EPA) Title V, landfills must prevent the escape of methane gas emissions through the installation of a Gas Collection and Control System (GCCS). In addition, EPA Subtitle D requires landfill operators to perform temporary or intermediate closure once individual landfill cells are full and then install a “final cap” once a landfill has reached its maximum permitted capacity and cannot be expanded. In December 2010, Progressive Waste Solutions (formerly IESI-BFI Canada) installed a new synthetic closure system on nine acres (3.64 hectares) of their Timber Ridge Landfill in Richwoods, Mo. The new system consists of three primary components: two layers of woven geotextiles with tufted UV-resistant polyethylene grass that is laid over a 50-millileter LLDPE structured drainage geomembrane and infilled with sand. The geomembrane layer serves as the containment liner atop the landfill’s intermediate soil cover. Integral 3.6 millimeter studs on the top surface facilitate drainage, while integral 4.4 millimeter spikes on the undersurface provide friction. The turf’s grass blades are interlocked with ¾ to 1 inch of sand ballast that, combined with the liner’s surface studs, provides sufficient interface friction to provide stability without the need for anchoring. The system is anchored for termination purposes only at the toe or on the outside of a perimeter swale, depending on the site design.

The client wanted to take a new approach in the industry by reducing these environmental and financial liabilities by using a cover system made out of geosynthetics, including the use of a synthetic turf layer that replaced the traditional erosive, vegetative soil layer. Traditional landfill closures are highly reliant on trucking soils, heavy civil construction and on-going maintenance and repairs in order to maintain their integrity. Even with diligent maintenance many fail subject to excessive erosion, gas pressure buildup, veneer sliding and severe weather events. Traditional closures are expensive, costing between $115,000 and $200,000 per acre to install and maintain during the EPA-mandated 30-year period. Additionally, they exact a high environmental price. The initial construction and reconstruction destroys land to borrow soil, creates sedimentation issues, consumes significant fuel and produces significant emissions from trucking and operation of heavy equipment. The client’s landfill had been plagued with a combination of erosion and maintenance issues and they wanted a closure system that would lower the capital costs and minimize the use of the operational resources for maintenance after closure. The landfill was also producing significant methane and the client wanted to take a proactive approach to capture the methane at early stages of generation.

The new approach combined two major elements of closure by using geosynthetics to capture methane and prevent water infiltration. Using a synthetic turf layer allowed for eliminating a soil cover component and providing stability even in severe weather conditions and seismic activity. The new approach also removed several thousand truckloads of dirt off the road, eliminated the need for mowing and vegetation maintenance such as fertilizer and replacement soil, and has quickly contained landfill emissions resulting in fewer greenhouse gasses released into the atmosphere. Compared to traditional closure methods, the project reduced its total carbon footprint from 652,400 kilograms of carbon dioxide per hectare (Kg CO2/ha) to 132,200 kilograms of carbon dioxide per hectare just in the construction, with an additional 500 cubic feet permit of landfill gas (with approximately 50 percent of the landfill gas being methane) captured by the geosynthetic system. This system also presented an important safety advantage. Under traditional landfill gas collection systems, constant monitoring and adjustments are needed to ensure that oxygen is not pulled into the landfill, leading to potential fire hazards deep within the waste mass. With no vertical wells serving as a pathway for oxygen, that is no longer a possibility at Timber Ridge. Maintenance costs on the gas collection system alone have been reduced by an estimated $53,000 per acre over a 30-year period.

This project demonstrates that new geosynthetic applications can improve the reliability and performance of landfill closures. In particular, adding a specialized synthetic turf component to an exposed geomembrane cap can improve membrane protection, accessibility, wind resistance and aesthetics. Additionally, the turf provides considerable economic and environmental savings. Construction and post-closure maintenance costs are reduced and the new system results in reductions in carbon dioxide emissions from the construction and the earlier capture of methane gas. With the new system, the client was also able to address the critical components of landfill operations - environmental closure and Gas Collection and Containment System (GCCS) - into one streamlined, cost-effective approach that reduced environmental impact. The integrated GCCS has allowed Timber Ridge to harvest greater amounts of high-quality methane that can serve as fuel for future green energy generation. Unlike gas collected through vertical wells, the emissions at Timber Ridge produce little condensate since the gas cools to ambient temperatures as it slowly rises toward the surface. The absence of vertical wells removes the potential for oxygen contamination and thereby increases the potency of the methane. Additional value will be realized in the near future in the sale of carbon credits and the development of landfill gas projects.

Project details

Location: Richwoods, Mo.
Size: 9 acres
Fabrics: Agru/Closure Turf ™ by Agru America, Inc. from Agru America, Inc.
Engineer and Design: Mark Russell, Aquaterra Environmental Solutions
Project Manager: Mike Friesen, Progressive Waste Solutions