Planning a Successful Landfill Liner Installation

There are many regulations and requirements associated with landfill installations. For example, when planning the installation of a new municipal solid waste landfill (MSWLF), three important federal requirements must be met: groundwater monitoring, closure and post-closure care, and financial assurance (1). These requirements are in addition to state regulations under the Resource Conservation and Recovery Act (RCRA). Navigating these regulations can be time-consuming, but it doesn’t have to be complicated. All regulations boil down to one essential function that must be built into all landfills: containment.

The federal requirements for groundwater monitoring highlights the importance of ensuring that landfill leachate does not contaminate groundwater sources. Geosynthetic liners are among the best tools that engineers can use to help ensure landfill containment. In this article, we will explore various landfill categories and their capabilities, how a landfill location can affect its design, and how to select the best landfill liners for the job.

Defining a landfill category and capabilities

The first step in planning a successful landfill liner installation is to determine what kind of landfill is required. Each type of landfill has a separate set of RCRA regulations that must be followed. For example, there are sets of RCRA regulations for creating landfills to hold nonhazardous waste or hazardous waste as well as regulations for creating underground storage tanks. MSWLFs are primarily governed by RCRA Part 258, which includes subparts for location restrictions, operation criteria, design criteria, groundwater monitoring, closure and post-closure care, and financial requirements (2). The design criteria outline a number of liner specifications including liner type, thickness, and installation requirements.

The liner, also referred to as the composite liner in the design criteria, is a two-part system comprising a flexible membrane liner (FML) and a two-foot layer of compacted soil with a hydraulic conductivity of no more than 1 × 10−7 cm/sec. The FML component can be made with high-density polyethylene (HDPE) at least 60 mil in thickness. Regardless of what FML component is chosen, it must be installed with direct and uniform contact with the underlying compacted soil component.

Choosing a landfill location and design

There are other factors that can also affect the landfill design. For instance, the hydrogeologic characteristics of the facility and the surrounding land. Hydrogeologic characteristics refer to groundwater and flow, existing groundwater quality, direction of flow, connection to drinking water reservoirs, and more. Understanding the hydrogeologic characteristics of the intended landfill location will help installers create appropriate groundwater monitoring systems as per federal requirements.

Other factors that can affect landfill design are climatic factors of the geographic region. For example, landfills installed on floodplains must demonstrate (1) that the landfill will not restrict the flow of 100-year flood events, (2) reduce the temporary water storage capacity of the floodplain, or (3) result in waste being washed out during a 100-year flood event. Of course, leachate will always be present so understanding the expected volume and physical/chemical characteristics of the leachate is important in order to plan adequate drainage.

Lastly, landfill design can be affected by landscape features such steep slopes, the availability of nearby clay, the composition of on-site subgrade, and more. These factors can require the installers to use structured geomembranes to improve slope stability of the liner with the subgrade, require the use of an alternative to compacted clay (e.g., geomembrane clay liner), and necessitate additional on-site prep prior to liner installation.