Landfilling: Bottom Lining and Leachate Collection

The critical element of a landfill, which is essential for the protection of the environment in general, and prevention of contamination of the underlying soils and groundwater in particular, is the bottom lining system. The major focus of the bottom lining system development is to prevent leachate from entering the groundwater or surface water. The bottom lining system should cover the full footprint area of the landfill, including both the relatively flat bottom and the sideslopes in the case of an excavated configuration. This prevents the lateral migration of leachate from within the landfill, as well as the migration of landfill gas, preventing contact between gas and groundwater. The bottom lining system is composed of a relatively impermeable liner or lining system. This very low hydraulic conductivity system controls the movement of the leachate out of the landfill. The bottom lining system works together with the overlying leachate management system, also referred to as the leachate collection and removal system (LCRS), which consists of a drainage layer that provides easy horizontal drainage of the leachate to a point of gravitational collection or pumping. Although individual liners, whether composed of soils or geosynthetic barriers, are able to prevent leachate emission to the environment for a relatively long time (50 years or longer), it should be realized that no liner is 100% efficient. However, modern lining systems, which include composite liners and multiple (double, or even triple) liners, are extremely effective in preventing leachate from entering into the environment. In addition, the risk of polluting the groundwater at a landfill by any leakage of leachate depends on several factors related to siting of the landfill: distance to the water table, distance to surface water bodies, and the properties of the soil beneath the landfill. In addition to the lining and drainage systems described in this chapter, the siting and hydrogeology of the landfill site (Chapter 10.12) and the top cover (Chapter 10.9) are also part of the barrier system, contributing to reducing the environmental risk associated with landfills. This chapter provides information about the materials used in the construction of liners and drainage systems, tools to calculate migrations through liners, as well as information about requirements for lining systems in the European Union (EU) and the United States (USA).