Landfill design has historically been based on a selection of design features from a range of alternative methods and measures to achieve a set of target objectives.
The primary requirement these days is containment. Containment has been set as an objective which can be achieved either by using predefined and accepted prescribed methods, or the designer may seek to achieve same result by one of a range of techniques according to availability of materials, and cost factors.
Rethinking Landfill is the subject of this video. Just take a look!
After a number of research studies were completed in very well controlled circumstances, by contractors observing good practice and closely monitored for their performance, it has been shown that large-scale engineering projects, say using HDPE plastic membranes or natural clay liners, still allow the passage of some flow. They leak!
It now has to be accepted that total perfection is rarely if ever achievable. It would furthermore be dangerous to assume that perfect construction without a single defect causing a small hole anywhere can be routinely achieved.
As a result designers and regulators have understood and come to accept the fact that all liners will allow some leakage. At another ‘materials technology’ level it is also a fact that even very low permeability materials like HDPE plastic membranes will pass a tiny flow through the material both water and gas, even when perfect.
Landfills are large, so a tiny and almost un-measurable flow through a small area becomes measureable when multiplied up by the huge areas of a modern landfill.
A probability distribution can be applied to each of the factors governing the rate of leakage for a given liner design, such that its probable leakage rate and consequent impact can be predicted by modelling.
The acceptability of a landfill design in the environment in which it will be placed should therefore be assessed by a process which quantifies the probable impact, or the probability distribution for an impact, of each source-term (typical concentration of a potentially damaging emission) on each relevant receptor, that is, the persons or features affected by it.
This process is known as risk assessment and should be used in an iterative way to produce an acceptable design.
By being used in an iterative way we simply mean that the designer or impact assessor starts by making a reasonable set of assumptions about a suitable landfill containment system. If at the first risk assessment stage it becomes clear that one or more of the impacts is unacceptable then the designer will repeat the assessment using a varied design having adjusted the design to reduce the excessive impact or impacts identified.
This process is repeated until an acceptable assessment has been achieved.
The process of environmental risk assessment will be governed by background levels set by the local regulatory authority, by statutory limits, and by policy.
These governing factors may, and probably will, change with time. The process by which risk assessment should lead to an acceptable quantified impact, and thereby after any necessary iteration, to an appropriate design, is outlined below.
· Identify all potential impacts.
· For each potential impact identify the source, the receptors or targets, and the pathway.
· Establish the sensitivity of the receptor, and the source term by geotechnical and other investigations.
· Derive a relationship between the landfill and the receptor using an agreed methodology and probability distribution for the source term and each element of the pathway
· Repeat this process to obtain a satisfactory design for the landfill consistent with an acceptable impact.
The process should be repeated iteratively for each potential impact until both an acceptable overall impact and an appropriate design for environmental protection is produced.
The risk assessment process should be applied to any quantifiable impact including, for example, leachate, landfill gas, traffic, noise and even public health risks one of which might be the potentially contaminative effects of seagulls, providing that the effects of mitigation can also be quantified.
Inherent in the use of probability based risk assessment is the possibility that improbable events might occur. In earthquake zones, for example, these will need consideration, while in river valley bottoms flooding might require consideration.
So, consideration should be given to possible responses to extreme events, and whether contingency measures need to be built-in from the start (for example, a leakage detection/interception system) or could be installed subsequently, in sufficient time, should the need arise (for example, a cut-off wall to hold back a leachate flow).
To allow for contingency measures which would be implemented as and when required, can be a practical option offering reduced initial costs, but may require pre-planning and in that there may be costs, such as in the acquisition and reservation of any necessary additional land.
For extensions of existing landfills, the risk assessment approach must take into account the effect of the existing waste and known levels of contamination which may be at present within acceptable limits but could be pushed over the edge by the additional pollutant loading from further landfill extension.
In some instances more stringent controls may be required, whereas in others it may no longer be appropriate to attempt to safeguard a damaged resource.
Steve Evans has written for the Wastersblog since 2006. It recently received nearly 50,000 hits in a month, and continues to grow. If you have any interest in free waste settlement ebook download-ready shouldn't you take a look?
Wednesday, 7 January 2009
Landfill Daily Cover and Landfill Specifications
Waste should not be treated differently to any other product, and then it would be possible for it to be recycled more easily. Waste once thus classified is too rigidly then held to remain waste, and this reduces its marketability due to the increased regulation which applies to waste when compared to normal industrial and manufacturing processes.
Waste if treated merely as a secondary resource with certain properties like should be able to move freely across borders and within regions. Why should, for example, a plastic cup made in one part of the world be able to be freely exported to another country, like the UK, but once recycled for material use become a restricted commodity?
“It does not make sense”.
Likewise with the issue of incineration; a furnace for a factory can be sited close to a conurbation and is welcomed and seen as creating jobs. Yet the same furnace burning waste is treated as a demon even though now that the EU Waste Incineration Directive has been implemented it will always have lower emissions than all of them.
Those working in the waste management industry must work to de-demonise the waste industry. If we lose this argument we are storing major problems for the future of the industry.
Nevertheless, for the foreseeable future there will still be waste which has to be disposed to landfill, so let us put our minds to that and the landfill specification needed..
A continuing trend in recent years has been to increase waste density through waste compaction. MBT waste itself tends to be dense and compactable. While this reduces settlement for the current generation the ultimate amount of settlement will depend upon the degree to which all organic material decompose to carbon dioxide or methane or other gaseous forms.
Increasing density will ultimately extend the period before a landfill reaches final storage quality when no more reactions are taking place and all soluble materials have been leachate out by into leachate by solution. Excessive waste compaction slows gas production and overall biological activity because as increases the density occurs, permeability reduces decreasing the rate at which water can infiltrate the waste.
Methane is produced by all modern landfills. It burns very easily and often is used as natural gas for cooking and heating. It is lighter than air and collects at the top of enclosed spaces. It can be profitably collected from landfills and used as an energy source.
The rate of gas production is higher if heavy rainfall and/or permeable landfill covers introduce additional water into a landfill, but EU policy and regulation is against such action.
Groundwater moves slowly and continuously through the open spaces in soil and rock below a landfill. If a landfill contaminates groundwater, a plume of contamination will occur.
Leachate, groundwater and landfill gas from landfill site are routinely monitored and where necessary treated, before being discharged to a nearby Publicly Owned Treatment Works.
Dumping rubbish in an uncontrolled manner occurs still in many developing nations. Such dumps provide a tempting livelihood for the very poor in many third world nations. If these sites are cleaned up in a socially sensitive manner there is scope for assisting the original tip scavengers to continue in a much more organised and efficient manner. There are some cleaned up dumps which now provide extremely profitable business for the ex-scavengers now turned business people.
Leachate migration control standards must be followed in the design, construction, and operation of landfills during the use of the facility and during the post-closure period.
Leachate is produced by a combination of liquids from waste material, rainwater and other liquids that are produced during the decomposition of waste. Leachate will initially contain contaminates that could pollute water supplies if allowed to enter the groundwater which is known as an aquifer where it is extensive enough to provide a water supply
Leachate is water that filters through the landfill, picking up impurities as it travels. If the impure water soaks down into an aquifer and reaches a well it will contaminate the drinking water.
Residents in some US states within one-half mile of the landfill may be able to have their wells tested every year. The Health Department contacts the owners or residents in the area of eligible properties before sampling each fall and spring. This is important as part of the landfill specification to protect the health of those using the well water.
Steve Evans has some great information and ideas on the environment and waste. Go visit his web sites for more articles like this one. For waste and recycling go to the Waste-rs Blog.
Waste if treated merely as a secondary resource with certain properties like should be able to move freely across borders and within regions. Why should, for example, a plastic cup made in one part of the world be able to be freely exported to another country, like the UK, but once recycled for material use become a restricted commodity?
“It does not make sense”.
Likewise with the issue of incineration; a furnace for a factory can be sited close to a conurbation and is welcomed and seen as creating jobs. Yet the same furnace burning waste is treated as a demon even though now that the EU Waste Incineration Directive has been implemented it will always have lower emissions than all of them.
Those working in the waste management industry must work to de-demonise the waste industry. If we lose this argument we are storing major problems for the future of the industry.
Nevertheless, for the foreseeable future there will still be waste which has to be disposed to landfill, so let us put our minds to that and the landfill specification needed..
A continuing trend in recent years has been to increase waste density through waste compaction. MBT waste itself tends to be dense and compactable. While this reduces settlement for the current generation the ultimate amount of settlement will depend upon the degree to which all organic material decompose to carbon dioxide or methane or other gaseous forms.
Increasing density will ultimately extend the period before a landfill reaches final storage quality when no more reactions are taking place and all soluble materials have been leachate out by into leachate by solution. Excessive waste compaction slows gas production and overall biological activity because as increases the density occurs, permeability reduces decreasing the rate at which water can infiltrate the waste.
Methane is produced by all modern landfills. It burns very easily and often is used as natural gas for cooking and heating. It is lighter than air and collects at the top of enclosed spaces. It can be profitably collected from landfills and used as an energy source.
The rate of gas production is higher if heavy rainfall and/or permeable landfill covers introduce additional water into a landfill, but EU policy and regulation is against such action.
Groundwater moves slowly and continuously through the open spaces in soil and rock below a landfill. If a landfill contaminates groundwater, a plume of contamination will occur.
Leachate, groundwater and landfill gas from landfill site are routinely monitored and where necessary treated, before being discharged to a nearby Publicly Owned Treatment Works.
Dumping rubbish in an uncontrolled manner occurs still in many developing nations. Such dumps provide a tempting livelihood for the very poor in many third world nations. If these sites are cleaned up in a socially sensitive manner there is scope for assisting the original tip scavengers to continue in a much more organised and efficient manner. There are some cleaned up dumps which now provide extremely profitable business for the ex-scavengers now turned business people.
Leachate migration control standards must be followed in the design, construction, and operation of landfills during the use of the facility and during the post-closure period.
Leachate is produced by a combination of liquids from waste material, rainwater and other liquids that are produced during the decomposition of waste. Leachate will initially contain contaminates that could pollute water supplies if allowed to enter the groundwater which is known as an aquifer where it is extensive enough to provide a water supply
Leachate is water that filters through the landfill, picking up impurities as it travels. If the impure water soaks down into an aquifer and reaches a well it will contaminate the drinking water.
Residents in some US states within one-half mile of the landfill may be able to have their wells tested every year. The Health Department contacts the owners or residents in the area of eligible properties before sampling each fall and spring. This is important as part of the landfill specification to protect the health of those using the well water.
Steve Evans has some great information and ideas on the environment and waste. Go visit his web sites for more articles like this one. For waste and recycling go to the Waste-rs Blog.
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