Landfill Liner
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A landfill liner, or composite liner, is intended to be a low permeable barrier, which is laid down under engineered
landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...
sites. Until it deteriorates, the liner retards migration of
leachate A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences wh ...
, and its toxic constituents, into underlying
aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...
s or nearby rivers from causing potentially irreversible contamination of the local waterway and its sediments. Modern landfills generally require a layer of compacted
clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
with a minimum required thickness and a maximum allowable
hydraulic conductivity In science and engineering, hydraulic conductivity (, in SI units of meters per second), is a property of porous materials, soils and Rock (geology), rocks, that describes the ease with which a fluid (usually water) can move through the porosity, ...
, overlaid by a
high-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or " polythene" when used for HDPE pipes. With a high strength-to-density rati ...
geomembrane A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are m ...
. The
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...
has stated that the barriers "will ultimately fail," while sites remain threats for "thousands of years," suggesting that modern landfill designs delay but do not prevent ground and surface water pollution. Chipped or waste tires are used to support and insulate the liner.


Types

Different types of liquid trash will vary in their chemical properties and threat posed to the local environment, so any individual landfills may use a variety of different liner systems depending on the type of trash that is collected there. There are two main types of liner systems in use: single-liner systems, and double-liner systems. Single-liner systems are generally used in landfills which hold
rubble Rubble is broken stone, of irregular size, shape and texture; undressed especially as a filling-in. Rubble naturally found in the soil is known also as 'brash' (compare cornbrash)."Rubble" def. 2., "Brash n. 2. def. 1. ''Oxford English Dictionar ...
waste from construction. Landfills with single-liner systems are not designed to contain harmful liquid wastes such as paint or
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black b ...
that could easily seep through a single-liner system. Double-liner systems are usually found in
municipal solid waste Municipal solid waste (MSW), commonly known as trash or garbage in the American English, United States and rubbish in British English, Britain, is a List of waste types, waste type consisting of everyday items that are discarded by the public. ...
landfills, as well all
hazardous waste Hazardous waste is waste that must be handled properly to avoid damaging human health or the environment. Waste can be hazardous because it is Toxicity, toxic, Chemical reaction, reacts violently with other chemicals, or is Corrosion, corrosive, ...
landfills. The first layer is constructed to collect the leachate, while the second layer is engineered to be a leak-detection system to ensure that no contaminants seep into the ground.


Components

Composite liners are required to be used in municipal solid waste systems for landfills and use a double liner system which is composed of a
leachate A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences wh ...
system which is a liquid that collects solids from the substance this is passed through it. The leachate system is surrounded in a by a type of solid drainage layer such as gravel which is enclosed by a geomembrane and compressed clay, also known as a
geosynthetic clay liner Different types of fabric used for geosynthetic clay liners Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported by geotextiles and/or ge ...
. This geosynthetic clay liner is usually made of sodium bentonite which is compacted in between two thick pieces of geotextile. The next material surrounding the composite liner would be a leak detection system composed of another material like gravel with an additional geomembrane or complex liner. The geomembranes within the composite liner consist of a high-density polyethylene which provide an effective minimization for flow and deliver and helpful barrier which is used on inorganic contaminants. It can be used as a substitute for sand or gravel and also has a very high transmissivity and low storage. The lower surface helps provide an effective leak test once correctly installed. It is also a low permeable vapor and liquid barrier. The geosynthetic clay liners are manufactured by factories and the purpose for it being made of sodium
bentonite Bentonite ( ) is an Absorption (chemistry), absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelli ...
is that they regulate the movement of liquids in gases within the waste. The geocomposites which are a combination of the geomembranes and geosynthetic liner material also include a layer of bentonite between the middle of the layers of geotextile; however, airspace is allowed to be implemented. It is then topped off with a final cover.


Mechanism

The main role a composite liner performs in a municipal solid waste system for landfills is reducing the amount of leakage through small seep holes that sometimes form in the geomembrane part of the composite liner. The protection layer part serves as a preventer from these holes from forming inside the geomembrane which would allow the waste to leak through the entire liner. It also takes away the pressure and stress which can cause cracking and holes from forming in the membrane as well. An effective liner in a landfill system should be able to control water in terms of movement and protection on the environment. It should be able to regulate the flow away from the waste area and withhold the waste contents as it enters the actual landfill. Due to the effectiveness on how landfills are placed on top of slopes in order for the water to stream downhill and in an emergency, into the actual landfill. Water moves through the landfill and downward through the composite liner. The main purpose for all of this is so that the movement is lateral which lessens the probability for slope catastrophe and the waste leaking down and freely contaminating whatever is in its path. The final cover functions as a way to keep the water out of the contaminate and to control the runoff from entering the system. This helps prevent plants and animals from being harmed by the waste contaminated water, leachate. Using gravity and pumps the leachate is able to be pushed to a
sump Sump may refer to: * An infiltration basin used to manage surface runoff water and recharge underground aquifers * Sump (cave), a permanently flooded section of a cave, where an underground flow of water exits the cave into the earth such that t ...
where it is removed by a pump. When developing composite liners it is extremely important to take in risk factors such as earthquakes and other slope failure problems that could occur. Composite liners are used in
municipal solid waste Municipal solid waste (MSW), commonly known as trash or garbage in the American English, United States and rubbish in British English, Britain, is a List of waste types, waste type consisting of everyday items that are discarded by the public. ...
(MSW)
landfill A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...
s to reduce
water pollution Water pollution (or aquatic pollution) is the contamination of Body of water, water bodies, with a negative impact on their uses. It is usually a result of human activities. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and ...
. A composite liner is made of a
geomembrane A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are m ...
along with a
geosynthetic clay liner Different types of fabric used for geosynthetic clay liners Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported by geotextiles and/or ge ...
. Composite-liner systems are better at reducing
leachate A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences wh ...
migration into the
subsoil Subsoil is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus. The su ...
than either a clay liner or a single geomembrane layer.


Mechanical properties

The primary forms of mechanical degradation associated with geomembranes result from insufficient tensile strength, tear resistance, impact resistance, puncture resistance, and susceptibility to
environmental stress cracking Environmental Stress Cracking (ESC) is one of the most common causes of unexpected brittle failure of thermoplastic (especially amorphous) polymers known at present. According to ASTM D883, stress cracking is defined as "an external or intern ...
(ESC). The ideal method of assessing the amount of liner degradation would be by examining field samples over their service life. Due to the lengths of time required for field sampling tests, various laboratory-accelerated ageing tests have been developed to measure the important mechanical properties.


Tensile strength

Tensile strength represents the ability for a geomembrane to resist tensile stress. Geomembranes are most commonly tested for tensile strength using one of three methods; the uniaxial tensile test described in ASTM D639-94, the wide-strip tensile test described in ASTM D4885-88, and the multiaxial tension test described in ASTM D5617-94. The difference in these three methods lies in the boundaries imposed into the test specimens. Uniaxial tests do not provide lateral restraint during testing and thus tests the sample under uniaxial stress conditions. During the wide-strip test the sample is restrained laterally while the middle portion is unrestrained. The multiaxial tensile test provides a plane stress boundary condition at the edges of the sample. A typical range of tensile strengths in the machine direction are from 225 to 245 lb/in for 60-mil HDPE to 280 to 325 lb/in for 80-mil HDPE.Sharma, Hari and Reddy, Krishna. 2004. Geoenvironmental Engineering: Site Remediation, Waste Containment, and Emerging Waste Management Technologies. John Wiley & Sons, Inc., Hoboken, New Jersey.


Tear resistance

Tear resistance of a geomembrane becomes important when it is exposed to high winds or handling stress during installation. There are various ASTM methods for measuring tear resistance of geomembranes, with most common reports using ASTM D1004. Typical tear resistances show a value of 40 to 45 lb for 60-mil HDPE and 50 to 60 lb for 80-mil HDPE.


Impact resistance

Impact resistance provides an assessment of the effects of impacts from falling objects which can either tear or weaken the geomembrane. As with the previous mechanical properties, there are various ASTM methods for assessment. Significantly higher impact resistances are realized when
geotextiles Geotextiles are versatile permeable fabrics that, when used in conjunction with soil, can effectively perform multiple functions, including separation, filtration, reinforcement, protection, and drainage. Typically crafted from polypropylene or ...
are placed above or below the
geomembrane A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are m ...
. Thicker geomembranes also display higher impact resistances.


Puncture resistance

Puncture resistance of a geomembrane is important due to the heterogeneous material above and below a typical liner. Rough surfaces, such as stones or other sharp objects, may puncture a membrane if it does not have sufficient puncture resistance. Various methods beyond standard ASTM tests are available; one such method, the critical cone height test, measures the maximum height of a cone on which a compressed geomembrane, which is subjected to increasing pressure, does not fail. HDPE samples typically have a critical cone height of around 1 cm.Kolbasuk, G. 1991. Coextruded Hdpe Vldpe Multilayer Geomembranes. Geotextiles and Geomembranes. 10, no. 5-6: 601-612.


Environmental stress cracking

Environmental stress cracking is defined as external or internal cracking in plastic induced by applied tensile stress more than its short-term tensile strength. ESC is a fairly common observation in HDPE geomembranes and thus needs to be evaluated carefully. Proper polymeric properties, such as molecular weight, orientation, and distribution, aid in ESC resistance. ASTM D5397 tandard test method for evaluation of stress crack resistance of polyolefin geomembranes using notched constant tensile load (NCTL)provides the necessary procedure for measuring the ESC resistance of most HDPE geomembranes. The current recommended transition time for an acceptable HDPE geomembrane is around 100 h.


See also

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Geomembrane A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are m ...
/
Pond liner A pond liner is an impermeable geomembrane used for retention of liquids, including the lining of reservoirs, retention basins, hazardous and nonhazardous surface impoundments, garden ponds and artificial streams in parks and gardens. Insta ...
*
Bioclogging Bioclogging or biological clogging refers to the blockage of pore space in soil by microbial biomass, including active cells and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass obstructs pore spaces, creatin ...
*
Biogas Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, Wastewater treatment, wastewater, and food waste. Biogas is produced by anaerobic ...
* Daily cover * Landfill mining *
Landfills in the United States Municipal solid waste (MSW) – more commonly known as Waste, trash or garbage – consists of everyday items people use and then throw away, such as product packaging, grass clippings, furniture, clothing, bottles, food scraps and papers. In 2 ...
*
Waste compaction Waste compaction is the process of compacting waste, reducing it in size. Garbage compactors and waste collection vehicles compress waste so that more of it can be stored in the same space. Waste is compacted again, more thoroughly, at the land ...


References

{{reflist, 2 Landfill Waste treatment technology Water pollution