Closing and capping the Timber Ridge Landfill

This project, submitted by Agru America Inc., won an Outstanding Achievement Award in the 2011 International Achievement Awards(IAA) / Geosynthetics presented by the Industrial Fabrics Association International. Each project in its own special way, exhibits outstanding innovation, technical skill and design excellence.

Submissions of geosynthetics projects for the 2011 International Achievement Awards are being accepted now. Submit your projects by July 15, 2012.

Introduction

Modern landfills operate under many federal and state regulations. Under the Environmental Protection Agency’s (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, the EPA’s 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 its Timber Ridge Landfill in Richwoods, Mo. The new system consists of three primary components:

1. two layers of woven geotextiles with tufted UV-resistant polyethylene grass that is laid over
2. a 50-milliliter LLDPE structured drainage geomembrane and infilled with
3. sand.

The geomembrane layer is the containment liner atop the landfill’s intermediate soil cover. Integral 3.6mm studs on the top surface facilitate drainage, while integral 4.4mm spikes on the undersurface provide friction. The turf’s grass blades are interlocked with ¾–1in. 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.

Landfill closure

The client in this case wanted to take a new approach in reducing environmental and financial liabilities by using a geosynthetic cover system, including the use of a synthetic turf layer instead of a traditional soil/vegetative layer.

The Timber Ridge Landfill in east-central Missouri had been plagued with a combination of erosion and maintenance issues, and the objective was a closure system that would lower 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.

Savings and safety

The new approach combined two elements of closure by using geosynthetics to capture methane and prevent water infiltration.

The decision to use a synthetic turf layer eliminated the soil cover component and promised stability even in severe weather conditions and seismic activity. This design 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 also contained landfill emissions resulting in significantly less greenhouse gasses released into the atmosphere.

Compared to traditional closure methods, the project reduced its total carbon footprint from 652,400kg CO2/hectare to 132,200kg CO₂/hectare just in the construction, with an additional 500ft³ of landfill gas (approximately 50% methane) captured by the geosynthetic system.

This system also offered safety advantages. Traditional landfill gas collection systems need monitoring and adjustments to ensure that oxygen is not pulled into the landfill, leading to potential fire hazards deep within the waste mass. With no vertical wells as potential pathways 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 during a 30-year period.

Conclusion

This project demonstrated 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. The turf also provides economic and environmental savings. Construction and post-closure maintenance costs are reduced and the new system results in reductions in CO₂ emissions from the construction and the earlier capture of methane gas.

The client was able to address critical components of landfill operations—environmental closure plus gas collection and containment—into one streamlined, cost-effective approach that also reduced environmental impact. The integrated GCCS has allowed Timber Ridge to harvest high-quality methane that can serve as fuel for future green energy generation. 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 could be realized with potential sales of carbon credits and the development of landfill-gas projects.