It was in 1991 that the Environmental Protection Agency promulgated its Criteria for Municipal Waste Landfills that set location restrictions, design and operating standards, groundwater monitoring requirements, corrective actions, closure requirements, and more for landfills. It was these rules that mandated that landfills be lined on the sides and bottom before waste is deposited and capped on the surface when closed.
Landfill liner systems are a critical element of the designs of new landfills, waste piles, and surface impoundments due to their essential functions: protecting soil and groundwater by isolating landfill contents from the environment and draining leachate to collection and treatment facilities.
“Society produces many different solid wastes that pose different threats to the environment and to community health,” The Ohio State University Extension has said. “Different disposal sites are available for these different types of waste. The potential threat posed by the waste determines the type of liner system required for each type of landfill.”
Sometimes used in landfills designed to hold construction and demolition debris, single-liner systems can employ a compacted clay liner, a geomembrane, or a geosynthetic clay liner. Compacted clay liners are typically at least 2 feet thick, and are designed to meet standards for hydraulic conductivity as well as to minimize cracks and imperfections that allow leachate migration.
Geomembranes, manufactured by combining plastic polymers with other ingredients, are designed to withstand the stresses of construction and the weight load of the waste. Geosynthetic clay liners employ hydraulic barriers such as bentonite clay supported by geomembranes or geotextiles. They are often used in places where clay is not available or conserving landfill air space is important.
Composite liners combine clay liners and geomembranes in systems that are more effective at limiting leachate migration. Because of this, composite-liner systems are required in municipal solid waste landfills. Combinations include:
- Geomembrane over a compacted clay liner
- Geomembrane over a geosynthetic clay liner
- Geomembrane over a geosynthetic clay liner over a compacted clay liner.
The geomembrane facilitates maximum leachate collection and removal while the natural soil layer serves as a backup in case of leakage.
A double lining consists of two single liners, two composite liners, as well as a single and a composite liner. The upper liner is designed to collect leachate with the lower one serving as a leak-detection system. Double-liner systems are used in some municipal solid waste landfills and all hazardous waste landfills.
Construction Quality Assurance and Quality Control
“Even the best unit design will not translate into a structure that is protective of human health and the environment, if the unit is not properly constructed. Manufacturing quality assurance and manufacturing quality control (MQA and MQC) are also important issues for the overall project,” notes an EPA report, Protecting Ground Water: Designing and Installing Liners. It says, “it is best to select a manufacturer who incorporates appropriate quality assurance and quality control (QA and QC) mechanisms as part of the manufacturing process.”
Agru America is the only U.S. manufacturer using the flat die extrusion calendered process to produce structured geomembranes for the U.S. and International markets. To ensure the highest quality, consistency and uniformity, suppliers deliver resin materials directly to Agru America production facilities in South Carolina and Nevada. There all material is sampled, checked against the supplier’s quality control certifications, tested and then approved before being released to production.