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In solid waste management, a geosynthetic liner takes on an important role in containment by preventing leachate from escaping into the surrounding environment. Ensuring a reliable barrier between the landfill contents and groundwater is especially important; for this reason, engineers must design landfills that meet several U.S. State and Federal regulations. At the top of the list for most requirements is geosynthetic liner thickness.
When analyzing the performance of a containment barrier, liner thickness is second only to installation and material quality. Liner thickness not only affects permeability, but also durability and service life. A thicker liner will last longer and is more likely to serve its purpose throughout the landfill’s operational life.
In this article, we will discuss the right liner thickness in designing a landfill, specifically looking at high-density polyethylene (HDPE). We will discuss minimum requirements and explain how approaching liner thickness from a different perspective can benefit the landfill and society in the long run.
Determining the minimum requirements for geosynthetic liners used in landfills
The minimum thickness HDPE liner for a new municipal solid waste landfill (MSWLF) is 60 mil according to the U.S. Environmental Protection Agency’s (EPA) Resource and Conservation and Recovery Act (1). While it may seem sufficient to design with the goal of meeting those minimum requirements, consider that the minimum can vary depending on how each State interprets EPA’s secondary requirements. Those secondary requirements are factors that can justify an increase in liner thickness including hydrogeologic characteristics of the surrounding land, climatic factors, and the physical and chemical properties of the leachate.
For landfills built in regions with heavy rain near the groundwater source of local towns, the State is likely to increase the liner requirements in addition to requiring a robust drainage system. Groundwater characteristics such as quantity, quality, direction, and flow as well as its likely use as drinking water are all factors that can impact landfill requirements.
Some countries consider all groundwater as a potential source of drinking water and have steadily increased the minimum requirements over the years. Many European countries, for example, have set 100 mil as the minimum thickness for polyethylene liners. While there are many differences between the United States and Europe, it is important to consider the underlying reasons why European countries have set higher standards for their landfill containment systems.
Reasons for designing above and beyond base requirements
The EPA recognizes that landfill proximity and its potential to impact local groundwater as important factors when designing landfills. However, they defer to the State when it comes to setting up the exact requirements. Differences in population density is likely a driving factor in EPA’s decision to leave the details for the States to decide, but landfills are designed to operate for decades. Is it a good long-term plan to allow land across the United States to have potentially contaminated groundwater?
The Covid-19 pandemic has revealed the potential for a single event to drastically change population behavior. The industrial revolution, for example, led to a migration into cities and Covid-19 led to a high degree of social distancing and isolation. Maintaining a clean environment is essential to not only protect local ecosystems, but also to ensure we do not waste potential livable space for future changes in social behavior.
The EPA also recognizes climate as an important factor in designing landfill containment. Regional weather patterns can help designers anticipate annual rainfall, which is a significant factor in calculating leachate production in a landfill. However, changes to weather patterns can result in some regions experiencing excess rainfall. Designing a containment system that can account for extreme weather events has become essential as climate patterns continue to shift.
Choosing the right products for a landfill containment system
Regardless of where you stand in the liner thickness discussion, geosynthetic manufacturers can produce a wide array of product configurations to meet your specific project requirements. AGRU America, for example, has been in the business of manufacturing plastic products and geosynthetics for more than 70 years. As the Plastics Experts, AGRU emphasizes the development of robust solutions that combine a variety of plastic technologies and technical expertise. Two recent AGRU innovations include CleanSeam and Conductive Liner.
CleanSeam is a protective strip on HDPE liners that installers can peel away to dramatically reduce the time required to prepare the liner’s welding zones. Conductive Liner is a coextruded geomembrane that contains a carbon layer that conducts an electrical charge, which is a requirement for some Construction Quality Assurance Testing. These product innovations are just some examples of how AGRU has remained at the forefront of the geosynthetics industry. By choosing AGRU, you get access to an expansive catalog of high-quality products. AGRU also offers robust customer service and technical feedback, including detailed drop-in specifications that your engineer can use in planning a design.
- 1. “Part 258 – Criteria for Municipal Solid Waste Landfills.” Electronic Code of Federal Regulations. Accessed online 15 June 2021. https://www.ecfr.gov/cgi-bin/retrieveECFR?gp=&SID=c94567294dff611654af7a3944a91d69&mc=true&r=PART&n=pt40.27.258#se40.27.258_140.