How to construct a Landfill Cap
The most crucial components of a landfill cap are the barrier layer
and the drainage layer. The barrier layer can be low-permeability
soil (clay) and/or geosynthetic clay liners (GCLs). A flexible
geomembrane liner is placed resting on the barrier layer.
Geomembranes are habitually supplied in sizeable rolls and are
available in quite a few thickness (20 to 140 mil), widths (15 to
100 ft), and lengths (180 to 840 ft). The candidate list of polymers
regularly used is drawn out, which includes polyvinyl chloride
(PVC), polyethylenes of various densities, reinforced
chlorosulfonated polyethylene (CSPE-R), polypropylene, ethylene
interpolymer alloy (EIA), and several newcomers. Soils used as
barrier materials in the main are clays that are flattened to a
hydraulic conductivity no greater than 1 x 10-6 cm/sec. Compacted
soil barriers are usually installed in 6-inch smallest possible
lifts to accomplish a thickness of 2 feet or more. A composite
barrier uses both soil and a geomembrane, taking advantage of the
properties of each. The geomembrane is in effect impermeable, but,
if it develops a leak, the soil component prevents noteworthy
leakage into the underlying litter.
For facilities lying on putrescible wastes, the collection and
manage of methane and carbon dioxide, potent greenhouse gases, must
be part of facility design and operation.
Concrete Cap/Asphaltic (Note Top-Seal can
be used in place of clay with better results at lower prices)
The most successful single-layer caps are composed of concrete or
bituminous asphalt. It is used to form a surface barrier sandwiched
between landfill and the environment. An asphalt concrete cap would
lessen leaching through the landfill into an adjacent aquifer.
Subtitle C Capping (Note Top-Seal can be
used in place of clay with better results at lower prices)
The RCRA C multilayered landfill cap is a baseline design that is
not compulsory for use in RCRA hazardous waste applications. These
caps normally consist of an upper vegetative (topsoil) layer, a
drainage layer, and a low permeability layer which consists of a
artificial lining greater than 2 feet of compacted clay. The
compacted clay liners are effective if they maintain a certain
moisture content but are prone to cracking if the clay matter is
dried out. Thus substitute cap designs are by and large considered
meant for arid environments.
RCRA Subtitle D Cap
RCRA Subtitle D requirements are for non-hazardous trash landfills.
The design of a landfill cover for a RCRA Subtitle D facility is in
the main a function of the foundation liner scheme or natural
subsoils there. The cover must meet the following specifications:
* the material should exhibit a permeability no greater than 1 x
10-5 cm/s, or equal permeability of any foundation liner or natural
subsoils present, whichever is less. This is where Top-Seal;
shines, It will make un-usable soils, Usable.
* The layer to keep the waste dry must contain at least 45 cm of
subsoil material type.
* The erosion prevention layer has to be not less than 150 mm of
subsoil material able to sustain indigenous flora development.
Different design can be considered, but must be remain of
corresponding performance as the specifications outlined above.
Altogether, covers should be designed to avoid the bathtub effect.
The bathtub effect occurs when a more permeable cover is positioned
above a less permeable bottom liner or natural subsoil. The landfill
then fills up approximating a tub.
