AREA A/B ENGINEERING REPORT - Waste Management

3.2 Liner System
Supervised installation of a HDPE geomembrane as
part of a composite liner system.
Geosyntec Consultants
The primary function of base liner systems in modern landfills is to protect groundwater from
contamination by landfill leachate. Liners are engineered low-permeability barrier systems that,
depending on local hydrogeological and climate conditions, use natural in-situ soils above the
groundwater table in conjunction with single, double, or composite soil and/or geosynthetic
materials. Beyond protecting groundwater, liner systems serve a number of important secondary
functions, including providing containment of waste, controlling landfill gas migration (i.e.,
protecting the local unsaturated zone and groundwater from gas impacts), and serving as a longterm
structurally stable base for overlying facility components. A composite liner system also has
a built-in back-up structure (the leachate collection system) to control downward movement of
liquid.
3.2.1 Liner System Components
Historically, compacting native (natural in-situ) or borrow-source clay or clay-rich soils has been
the favored method of containing leachate within the landfill. The use of clay soils can be
effective as a natural liner system and can exceed minimum performance standards. However,
where climatic and geologic conditions preclude the use of in-situ soils as an effective natural
barrier system, modern landfill designs also feature single or multiple layer liner systems.
Multiple layered (or composite) liners feature
one or more liner components that comprise the
composite barrier system. The most common
geosynthetic liner material in use today is a
geomembrane (GM), or flexible membrane liner
(FML), which is manufactured and installed by
independent, third party contractors in
accordance with protocols for quality control
and quality assurance. Due to its resistance to
degradation by a wide range of chemicals,
among other factors, high density polyethylene
(HDPE) geomembrane is the most common type
of GM barrier used in landfill liners. However,
other GM materials include polyvinyl chloride (PVC), butyl rubber, and hypalon. In a typical
installed composite liner, a GM forms the upper component, with compacted in-situ soils,
compacted clay liner (CCL), or a geosynthetic clay liner (GCL) as the lower component(s).
MD10186.doc 37 29 March 2009