The great cover-up

Collecting and treating landfill leachate keeps getting more expensive. Increasing regulations along with rising municipal treatment plant costs make it more important than ever to discover new ways to reduce leachate generation. Different strategies are important to consider, but one specific method can be simple and cost-effective—a cover-up.

Not the kind of cover-up that would lead to an investigation by authorities but the use of a temporary exposed geomembrane cover (TEGC) to block rainfall from infiltrating buried waste and generating leachate. A TEGC has between two and seven years of service life. Identifying the right area to use the TEGC, and then making the right choices in design and product selection, can lead to cost-saving benefits and budget reductions.

Solid waste regulations differ from state to state, but most require interim cover, typically soil, for exposed waste that is generally 180 days or more away from final closure. Waste in this scenario may reside under 12 to 24 inches of generic cover soil with varying degrees of compaction.

Over time, the effectiveness of this cover soil in preventing the infiltration of precipitation diminishes, and generated leachate can be as much as that from uncovered waste. TEGCs are synthetic barrier materials made to block and shed precipitation away from contributing to leachate. Typically placed atop a reduced layer of cover soil, a TEGC can be designed for multiyear life expectancy and can be strategically positioned to cordon off large sloped and flat areas until a permanent closure solution is required.

TESTING AND LEARNING

Owens Corning, a Toledo, Ohio-based manufacturer of fiberglass insulation and other building products, owns and operates multiple industrial solid waste disposal facilities throughout the United States. Owens Corning also manufactures the woven coated polyethylene RhinoSkin, a product line for various design-life TEGCs. An opportunity to conduct a study was presented when the Owens Corning Newark Insulation Plant in central Ohio inquired about its use for the management and reduction of leachate generation and treatment costs for its own landfill. The goal of the study was to quantify real-world performance of TEGCs in landfill operations.

The plant resides on 86 acres, about 40 miles east of Columbus, housing the manufacturing of glass fiber batts and rolls, industrial ceiling boards, pipe and HVAC products. Adjacent to the plant is a 149-acre industrial solid waste landfill, owned and operated by Owens Corning. The landfill is permitted to receive industrial solid waste generated by the plant.

Leachate generated from buried landfill waste is collected and treated in an on-site facility at the Owens Corning plant. Although the landfill benefits from a leachate recirculation system, expanded disposal areas over 30 years of operation have gradually increased treatment demand to the point where capacity is diminishing. Owens Corning staff were drawn to potential solutions that could lessen the leachate generated without the addition of expensive clay soils typically used in final closure cover designs.

The Owens Corning Science and Technology group, located in nearby Granville, teamed up with plant operations to design and test a solution. The test was designed to compare three RhinoSkin geomembranes of various thicknesses for performance, ease of installation, durability and cost as TEGCs atop interim soil cover. The test also was designed to quantify the reduction of leachate generation compared with areas of the landfill without the TEGC.

MEASURING PERFORMANCE

The study used 16-, 20- and 24-mil-thick RhinoSkin geomembrane covers, each measuring approximately 80 square feet. The total TEGC coverage area was approximately 80 feet by 240 feet, or 19,200 square feet (0.44 acres). Planners agreed on RhinoSkin placement just outside of active disposal in an area anticipated to receive a new lift within the next six to eight months.

Under each different TEGC, a bucket lysimeter was placed about 4 feet below the existing cover soil, residing partially within the buried waste. The lysimeter is a device configured to collect infiltration at a certain soil depth with means to periodically pump out and measure seepage over a given time. For this study, a lysimeter was placed under each TEGC, but also in uncovered adjacent areas to compare infiltration rates and volumes.

Installation of the TEGCs used two practices to significantly reduce time and labor. First, each of the TEGCs was prefabricated, minimizing measuring, cutting and welding in the field. Depending on the thickness of RhinoSkin material used, TEGCs can be fabricated to cover up to an acre with no additional field welding required. For this study, the three RhinoSkin panels were prefabricated in empty indoor space of the adjacent insulation plant and transported for deployment.

Owens Corning Science and Technology sought a way to secure the TEGCs from wind uplift without having to use sandbags. Sandbags can degrade in the sun and lose effectiveness in holding down the cover well before the cover is no longer needed. Using a more UV-resistant sandbag can be expensive, especially when coupled with the cost of filling, moving and roping the bags to place them approximately 8 to 10 feet apart.

Instead of sandbags, the TEGCs were installed using various types of earth percussion anchors. These anchors are engineered securing devices designed for civil applications. Owens Corning Science and Technology used a wind uplift calculation procedure to determine the size and spacing needed for the anchors to resist wind speeds at the landfill.

UNCOVERING THE BENEFITS

After four months of data collection and observation, the study was deemed successful. First, the installation of the prefabricated RhinoSkin panels reduced the estimated time of field sewing or welding by almost 40 percent and had the added assurance of higher quality seams. Second, the cost reduction using earth percussion anchors instead of sandbags was more than 60 percent.

Perhaps the most significant benefit was leachate reduction of more than 75 percent. The RhinoSkin TEGCs were effective in blocking and diverting rainfall that would otherwise infiltrate and generate leachate.

Owens Corning believes the right thing to do is share this success with other landfill owner-operators. Owens Corning Science and Technology will publish the full findings of the study in a paper titled “Quantified Leachate Reduction Using Innovative Temporary Exposed Geomembrane Covers.”

Included within the paper is a comprehensive description of the study and the results, along with design guidance in product selection and placement to engineer cover solutions for landfill applications and other disposal sites. The paper will be available in upcoming technical publications and at future waste management conferences and seminars.

As for the cover-up, it now looks as though the means and methods for using a temporary geomembrane cover solution to reduce leachate generation have been exposed. And that’s good for the entire landfill industry.

Andy Durham, P.E., is the senior geosynthetics engineer for Owens Corning Science and Technology, Granville, Ohio.