Landfill: Difference between revisions

*initial choice of location

*the engineering and containment systems

*the operational management

*the restoration and closure of the landfill

*the monitoring of landfills through each of the above stages

The placement of waste in a landfill will slowly degrade over time, and in the case of the presence of [[Organic Waste]] within the [[Residual Waste]] going to landfill, it will breakdown to produce '''Landfill Gas''' and '''Leachate''' which have the potential to cause environmental pollution. As a result the selection of the site and the engineering and containment design to protect the environment, and specifically underlying groundwater, is critical to the successful delivery of a modern landfill.  

*Waste Management Paper 26B (WMP26B)<ref name="refB">Waste Management Paper 26B (WMP26B): Landfill Design, Construction and Operational Practice</ref>

*Waste Management Paper 26A (WMP26A)<ref name="refA">Waste Management Paper 26A (WMP26A): Landfill Completion</ref>

*Waste Management Paper 27 (WMP27)<ref name="ref27">Waste Management Paper 27 (WMP27): Landfill Gas</ref>

===Leachate===

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.

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.

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.

I 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.

The underlying geology and hydrogeology of a landfill is especially significant if there is an '''aquifer''' that is relied upon for drinking water or other extraction purposes. One definition of aquifer is from Freeze and Cherry (1979): “''An aquifer is best described as a saturated permeable geologic unit that can transmit significant quantities of waste under ordinary hydraulic gradients''”.  

In the England and Wales, the [[EA]] categorize aquifers to be consistent with the [[Water Framework Directive]]. The categories are Principal Aquifer, Secondary Aquifer and Unproductive Strata. Previously the phrases major aquifer and minor aquifer were utilized. Similar arrangements exist in Scotland and are supervised by [[SEPA]].

The relevance of the hydrogeological setting within which a landfill is located arises from the need to assess the technical precautions and engineering requirements for a landfill to be authorized such that unacceptable environmental impacts are prevented. This assessment is undertaken via a '''Hydrogeological Risk Assessment''' ('''HRA'''); this is submitted as supporting document to an [[Environmental Permit]] application and takes a risk based approach to the location of the landfill and the engineering required. Again, similar arrangements are in place in Scotland, Wales and Northern Ireland.  

In the case of Principal Aquifers, which are of the highest quality and use, it is unlikely that any HRA will come to the conclusion, even with extensive engineering, that a landfill will be able to be located above such an aquifer (see Landfill location below).

Landfill engineering is a phrase used to describe the preparation and on-going engineering required to operate a landfill site, and overall design, approach and engineering solution is often referred to as a whole as a '''containment system'''. What is required at any particular site in the UK depends upon the proposals made by the permit holder to protect the environment as part of obtaining an [[Environmental Permit]] (with the HRA and the containment system and engineering design being a key part of any such submission) and any subsequent modifications agreed between the permit holder and the regulator ([[EA]], [[NRW]] or [[SEPA]]).

Notwithstanding the risk-based technical design of the landfill engineering, there are minimum requirements imposed by the Landfill Directive and subsequent UK legislation – [[The Landfill (England and Wales) Regulations 2002]] and the [[Landfill (England and Wales) (Amendment) Regulations 2005|Landfill Regulations 2005]].

The design will have been produced taking heed of the technical precautions required to satisfy the regulator that the site will not have an unacceptable impact upon the environment and  that the approved design will comply with the requirements of the Landfill Directive. These precautions will have been validated against the various risk assessments required to accompany a permit application.

Sites which were authorised historically did not require engineering and such sites without an engineered lining system are commonly described as “'''dilute and disperse'''”. Notwithstanding the lack of site engineering, some evaluation of their pollution potential was undertaken. This mainly consisted of a simple evaluation of the ability of the surrounding geology to adsorb contamination to determine likely consequential pollution effects. This evaluation considered the ability of the ground to “'''dilute and disperse'''” the impact of the site, hence the common name.

Landfill engineering design evolved in the 1980s, such that new '''dilute and disperse''' sites became less likely to be granted consent by the regulator. At the time, this was not supported by the implementation of any new specific legislative drivers, the principal legislation remaining the [[Control of Pollution Act 1974]]. This required landfills to be licensed by local authorities. In assessing licence applications, local authorities were required to ensure the prevention of pollution to water and danger to public health. This requirement established a rationale for assessment and its implementation evolved over the period from 1976 onwards. With the introduction of subsequent legislation mentioned elsewhere on this page, the regulatory role moved from local authorities to the [[EA]] (and in due course the [[NRW]], [[SEPA]] and [[NIEA]]) and coincided with the Landfill Directive and Groundwater Directive which set minimum standards and requirements.

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.<br>

Another product of waste decomposition is landfill gas. This is a mixture of various components, principally methane. WMP28B<ref name="refB" /> also contains a useful review of the generation and evolution of landfill gas.

Management of landfill gas consists of prevention of migration and escape by containment barrier, active removal of the gas from the waste mass by extraction and subsequent destruction.

 

Landfill gas can be utilised for energy generation – principally electricity generation – as well as simple destruction by combustion in a flare.

<ref name="ref27" /> deals with methods for management of landfill gas.

# various ancillary equipment to maintain dust suppression, surface water control and to deal with pests and birds<br>

Commonly, the capping layer will consist of a compacted clay layer of 1 metre thickness. This can be replaced or supplemented by flexible membranes such as LLDPE (Linear Low Density Polyethylene) or GCL (Geo-synthetic Clay) in varying combinations. Membranes can be laid in an over-lapped with no fused joints or can be overlapped and welded together similar to lining systems.

Gas and leachate extraction and monitoring equipment (such as monitoring well and pipework) commonly penetrates the capping and soil layers in order to afford access for maintenance and monitoring. Sometimes this equipment is progressively buried with suitable access points remaining at the surface; this is done principally for aesthetic reasons to improve the appearance of the final restored surface.

The landfill operator is required to continue to maintain monitoring and management of the site post-closure until it can be shown to the satisfaction of the EA that the active management of the site by the operator is no longer required. Assessment of such a state is measured against criteria identified in WMP 26A and subsequent EA guidance. It is generally accepted for non-hazardous landfill sites that this is unlikely to be able to shown for at least 60 years post-closure, probably somewhat longer. This period is known as the '''aftercare''' period.

 

As the waste mass decomposes, the fill material settles under its own weight to occupy less volume. This process is known as '''settlement'''.

== Landfill Monitoring ==