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Landfill: Difference between revisions
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Putrescible waste placed in landfill sites undergoes decomposition. This is also described in WMP26B<ref name="refB" />. The process gives rise to a liquid known as leachate. Leachate arises from water entering the waste matter, generally from rainfall on open areas of waste. 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. Landfill leachate is strongly polluting in the external environment; one of the principal reasons for constructing landfill sites as containment facilities is to prevent landfill leachate from escaping from the waste mass in an uncontrolled manner. Escape of Leachate into the underlying groundwater is a key factor in assessing the location of a landfill and the engineering containment systems to be design. | Putrescible waste placed in landfill sites undergoes decomposition. This is also described in WMP26B<ref name="refB" />. The process gives rise to a liquid known as leachate. Leachate arises from water entering the waste matter, generally from rainfall on open areas of waste. 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. Landfill leachate is strongly polluting in the external environment; one of the principal reasons for constructing landfill sites as containment facilities is to prevent landfill leachate from escaping from the waste mass in an uncontrolled manner. Escape of Leachate into the underlying groundwater is a key factor in assessing the location of a landfill and the engineering containment systems to be design. | ||
Once the design of sites moved from dilute and disperse to containment designs, as shown in the previous cross-sectional diagrams, it became necessary to devise means of avoiding leachate from building up excessively within the waste mass. There are two drivers for this: (i) in extreme circumstances, the volumes could lead to levels over-topping the sides of any containment structures and leaving the site, and (ii) designing the site to maintain levels at a level as low as practically possible would improve the HRA outcome for any given design. Consequently, sites were designed with means to collect and remove leachate. | Once the design of sites moved from dilute and disperse to containment designs, as shown in the previous cross-sectional diagrams, it became necessary to devise means of avoiding leachate from building up excessively within the waste mass. There are two drivers for this: (i) in extreme circumstances, the volumes could lead to levels over-topping the sides of any containment structures and leaving the site, and (ii) designing the site to maintain levels at a level as low as practically possible would improve the Hydraulic Risk Assessment (HRA) outcome for any given design. Consequently, sites were designed with means to collect and remove leachate. | ||
Leachate removed from the waste mass needs to be disposed of in an appropriate fashion. In general, this requires transmission to an appropriate treatment plant; this might be via a connection to the sewer system for ultimate treatment at an off site sewage treatment plant operated by a utility company, or an on-site private leachate treatment plant. Depending upon the capacity at the receiving utility treatment plant, leachate may require pre-treatment at the landfill site prior to sending to the offsite sewage treatment plant. | Leachate removed from the waste mass needs to be disposed of in an appropriate fashion. In general, this requires transmission to an appropriate treatment plant; this might be via a connection to the sewer system for ultimate treatment at an off site sewage treatment plant operated by a utility company, or an on-site private leachate treatment plant. Depending upon the capacity at the receiving utility treatment plant, leachate may require pre-treatment at the landfill site prior to sending to the offsite sewage treatment plant. | ||
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In the case of an on-site leachate treatment plant, once appropriate quality standards have been met it may discharge to a receiving watercourse or (less frequently) a soak-away. Such a discharge would be regulated by the [[EA]] with an [[Environmental Permit]]. Discharge to a sewer, with or without pre-treatment, would require agreement with the relevant utility company as an industrial effluent. | In the case of an on-site leachate treatment plant, once appropriate quality standards have been met it may discharge to a receiving watercourse or (less frequently) a soak-away. Such a discharge would be regulated by the [[EA]] with an [[Environmental Permit]]. Discharge to a sewer, with or without pre-treatment, would require agreement with the relevant utility company as an industrial effluent. | ||
In the event that no on-site treatment is possible, and no local connection to the sewage system is possible, Leachate may also be taken to an off-site facility (e.g utility sewage treatment works) via road-going tanker for treatment and disposal. | |||
=== Groundwater and Hydrogeology === | === Groundwater and Hydrogeology === | ||
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The Landfill Directive sets out minimum requirements for site engineering. In simple terms, all sites require a "geological barrier" and some sites are additionally required to have an "artificial sealing liner". The most common manner in which these requirements are deal with is by having a clay liner of 1m metre thickness of low permeability engineered clay (permeability of less than 1x10-9 metres per second) overlain with 2mm thick welded HDPE (high density polyethylene) lining membrane. Typically, this would be further overlain with a geotextile protection layer and then a drainage layer of aggregate and pipework. A typical installation is shown below. | The Landfill Directive sets out minimum requirements for site engineering. In simple terms, all sites require a "geological barrier" and some sites are additionally required to have an "artificial sealing liner". The most common manner in which these requirements are deal with is by having a clay liner of 1m metre thickness of low permeability engineered clay (permeability of less than 1x10-9 metres per second) overlain with 2mm thick welded HDPE (high density polyethylene) lining membrane. Typically, this would be further overlain with a geotextile protection layer and then a drainage layer of aggregate and pipework. A typical installation is shown below. | ||
[[File:Landfill lining.jpg|300px|left|Typical installed HDPE liner]] | [[File:Landfill lining.jpg|300px|left|Typical installed HDPE liner]]__TOC__ | ||
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a series of Waste Management Papers (WMP)<ref name="refB" /><ref name="refA" /><ref name="ref27" /> over the period from the late 1970s to 1997. WMP 26B contains a review of the types of designs. The design employed at any particular design would be informed by the outcome of the HRA which would assess the likely impact of a site upon the environment taking account of the design proposed. In general terms, the most sensitive sites would require the greatest degree of engineering. | The Department of the Environment produced a series of Waste Management Papers (WMP)<ref name="refB" /><ref name="refA" /><ref name="ref27" /> over the period from the late 1970s to 1997. WMP 26B contains a review of the types of designs. The design employed at any particular design would be informed by the outcome of the HRA which would assess the likely impact of a site upon the environment taking account of the design proposed. In general terms, the most sensitive sites would require the greatest degree of engineering. | ||
Landfills are constructed in discrete parts known as “[[Landfill Cell|landfill cells]]”. The sub-division into cells is undertaken so as to minimise the operating area and consequently minimise leachate generation and make the site more manageable in terms of odour and litter control. Sub-division also enables the site engineering to be constructed progressively as the site fills. | Landfills are constructed in discrete parts known as “[[Landfill Cell|landfill cells]]”. The sub-division into cells is undertaken so as to minimise the operating area and consequently minimise leachate generation and make the site more manageable in terms of odour and litter control. Sub-division also enables the site engineering to be constructed progressively as the site fills. | ||
===Landfill Gas=== | ===Landfill Gas=== | ||
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Management of landfill gas consists of the prevention of build up by active removal of the gas from the waste mass by extraction (and subsequent destruction by high temperature flare or via the creation of energy for subsequent use on site or for export ot the national grid) and the prevention of migration and escape by the containment barrier/lining system and the restoration/capping systems. WMP27<ref name="ref27" /> deals with methods for management of landfill gas. | Management of landfill gas consists of the prevention of build up by active removal of the gas from the waste mass by extraction (and subsequent destruction by high temperature flare or via the creation of energy for subsequent use on site or for export ot the national grid) and the prevention of migration and escape by the containment barrier/lining system and the restoration/capping systems. WMP27<ref name="ref27" /> deals with methods for management of landfill gas. | ||
[[File:Landfill Gas Engine.jpg|300px|left|A typical landfill gas engine]] | {| class="wikitable" | ||
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| [[File:Landfill-gas-flare.jpg|300px|left|Landfill gas flare - source Hoffsetter]]|| [[File:Landfill Gas Engine.jpg|300px|left|A typical landfill gas engine]] | |||
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|'''Landfill Gas Flare'''||'''Landfill Gas Engine''' | |||
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==Landfill Location Policy in the UK== | ==Landfill Location Policy in the UK== | ||