There are a lot of elements in the argument for and against phased restoration of a landfill. Well before making your decision, it’s going to be important and vital to make sure you know and fully grasp these pros and cons. This article explains some of the important plusses and minuses associated with the development, operation and restoration of landfills in a series of phases of sufficient size for efficient landfill operation.

The method of landfilling is known as phased restoration. It has many advantages, and in many national waste regulation regimes is considered to be a central requirement of sanitary landfill practice, and to show a well planned Restoration Phasing Plan is a pre-requesite of obtaining any site licence. In a number of the industrializing nations this does not apply which appears surprising when there are such huge benefits in:

• increase landfill gas yield
• reduced leachate production.

However, the requirements of pregressive restoration interact with other site aspects, and it is unlikely that all angles can be obtained perfectly at any given site. To be able to make the decision which is correct for you, you will need to know the following:

Benefits: Points In Favor Of phased restoration of a landfill

1. Landfill development should be based on the progressive use of the landfill area, such that at any given time parts of the site may be in the process of being:

- capped and restored
- capped
- actively filled
- prepared to receive waste, or as yet undisturbed,

and the aim of the restoration program is always designed to minimize incident rainfall soaking into the waste, and maximize early completion of discrete areas (Phases) to the final restoration profiles to allow maximum landfill gas extraction from full depth vertical landfill gas wells.

2. It allows progressive restoration. Progressive excavation of on-site materials, allows for efficient nearby storage of restoration materials, and minimisation of double handling of development and restoration soils.

One other good reason for the advance planning, development, operation and restoration of landfills in a series of phases, of sufficient size for efficient landfill operation, is minimisation of double handling of development and restoration soils.

This has the additional advantage of avoidance of unnecessary earthworks soils materials handling, that is certain to protect against making the mistake of large quantities of restoration materials being found to be needed toward the end of the landfill period, when otherwise useable material is then covered with waste and cannot be excavated and used.

3. It minimises the area required for active landfill operations and concentrates activities within a sequence of defined areas, reducing nuisance and polluting emissions.

And then there’s less visual intrusion caused by the landfill, and also site restoration funding requirements are more progressve and less peaky.

All these are advantages for the site that is continuously restored and each restoration work construction period is carried out by the site owner every year to 18months. It’s also very important as it could otherwise mean that without progressing restoration very large areas of only temporarily covered unsightly waste would be left for longer, for the alternative non-phased restoration of a landfill.

Also, perhaps all of us will agree that it must surely be best to plan full height restoration, and avoid large areas of waste left open and uncapped for long periods. Once you take that under consideration, then it makes sense to plan, and implement a plan, for phased landfill restoration using progressive restoration techniques.

The points above show the positive aspects of phased restoration of a landfill. There exists a down side also. Here’s a discussion of some of the drawbacks, but never overestimate the drawbacks!

Drawbacks: Arguments Against phased restoration of a landfill.

1. Physically excessively placing a limit on operational space

If you consider the phased restoration of a landfill, some parts may be too steep for the restoration works plant, within the phasing plan – especially for very deep landfills may limit operational space. That’s clearly a bad thingbut should be avoidable with good planning in most cases and all but the narrowest and deepest “quarry filling” landfills.

2. The direction of phasing usually needs to be resolved between screening for visual, wind and noise and allowing adequate flexibility for the passage of vehicles across the site.

Other factors to consider which will be present for the designers of many phased landfills will be

- potential instability in part-filled void, where support from future waste is absent
- need for protection of temporary edge of lining/capping
- need to protect against leachate overflow into unlined areas
- achievement of agreed final landscape plan after settlement.

3. Achieving the normal preference for leachate drainage to start at lowest point, may conflict with topographical requirements

The last pssible justification put forward to avoid phased restoration of a landfill is achieving the normal preference for leachate drainage to start at lowest point admittedly, this may conflict with topographical requirements. Everyone ought to consider this point very carefully, considering the fact that it can cause difficulties later with leachate wells in difficult to access or excessively deep locations if you decide to go for the phased restoration of a landfill. However, despite the complexities of phased landfill design, the fact is that it is genuinely the best option for probably about 90% of MSW landfills.

And so that’s that. There are the positives and negatives of phased restoration of a landfill. It may not be the right thing for some rare landfills, but it is most certainly beneficial to nearly all MSW landfill operations. So, you should carefully look at the above information and comparisons. Hopefully your final decision process will be aided in detail because of the pro and con info offered here.

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The most critical components of a landfill cap are the barrier layer and the drainage layer. The barrier (sealing) layer can be low-permeability soil (clay) and/or made from geosynthetic clay liners (GCLs).

A flexible geomembrane liner may also be required and if so, is placed on top of the barrier layer. In addition for stoney sub-soil materials a protection geotextile “blanket” may be needed, over and/or below the flexible geomembrane liner.

The soils used as barrier materials are usually clays that are compacted to a hydraulic conductivity no greater than 1 x 10-9 m/sec for UK landfills generally, but less stringent permeabilities may be justifiable and may be used where acceptable to the Environmental Regulator (UK – EA).

Compacted sealing layers are generally installed in 200mm minimum lifts to achieve a thickness of 600 mm or more.

Many people talk of using a composite capping system. A composite cap/barrier uses both soil (clay usually) and a geomembrane, and making best of the advantages of the properties of each. A geomembrane when installed is essentially if intact so impenetrable by water to be thought of as impermeable, but if it geomembrane barrier develops a leak, the soil component provides a second line of defence and prevents significant leakage into the underlying waste.

The purpose of landfill capping is to shield humans and the environment from the harmful effects of the landfill contents and limit the migration of the contents by reducing inflow of water from the surface, and greatly reducing gas escape. A cap will always restrict surface water infiltration into the contaminated landfill contents to reduce the possibility of contaminants leaching from the site after landfill closure.

A Landfill capping Landfill Capping is the most common form of remediation because it is generally less expensive than other technologies and effectively manages the human and environmental risks connected with a remediation place. That being said, the process of capping is still very expensive

Hydrogeological studies must be carried out to guarantee the drainage of any water that, by running between the membrane and soil mass, can reduce to zero the soil/membranes’ coefficient of friction. If such a situation was present the soil mass overlying the impermeable membrane would become unstable at many landfils subject to slippage in a veneer fashion.

The Geosynthetic material known as “Pozidrain” may be able to provide these functions with higher performance and lower cost than conventional crushed stone filters. Also, Pozidrain is also used by landfill operators who want to gain the revenue from every last once of waste into their landfill before landfill closure. The thickness of this material makes this possible as it is much thinner than a stone layer. This allows more waste to be put in the landfill before the planning consented top of site levels are attained.

Pozidrain has been specially designed to be compatible with both HDPE and clay liners and to give the optimum performance over the whole life of the landfill closure capping. Pozidrain will enhance the performance of the GCL or HDPE liners by providing an additional barrier that prevents the majority of the water or gas reaching the liner.

The need to manage leachate and landfill gas will continue until the wastes contained within a site no longer have the potential to cause problems in their specific location. In fact the pressure to maximize landfill gas and thus improve the amount energy obtained from waste is bound to continue to rise.
This fact is emphasised by the Waste Regulations and Environment Agency Permitting requirements, with landfill operators being legally obliged to introduce and maintain long-term aftercare regimes which, in the case of landfill gas control and leachate management, may have to continue for many decades.

It is not possible to define exactly the point at which wastes can no longer be considered to pose a potential environmental threat. The period of time necessary for a landfill to reach environmental stability is very much related to the nature of the wastes and the rate of the decomposition processes at work within the body of wastes.
In many ways, the development of modern landfilling techniques, and particularly the move towards containment landfills, can tend to slow down rather than speed up the rate of stabilization of the wastes.

It is a recognised fact that the rate of stabilization can be maximised by raising the moisture content of the landfill, but this is hard to do without allowing a zone of saturation to develop within the landfill. This may result in several metres of leachate being allowed to develop above the basal liner.

Such an approach has significant benefits since it is much more likely that stable, methanogenic conditions can be established at an early stage, recirculation of leachate is made easier, and the processes of leachate stabilization and landfill gas production can be better controlled.

However, this approach is in direct conflict with the engineer’s wish and overriding need to protect the liner system by minimizing leachate heads and preventing infiltration. This conflict, which is a real one and not just theoretical, has to be addressed by the landfill industry.

As the industry moves towards the concept of “Bio-reactor” landfills it is essential that the desire to control the complex processes at work within the landfill – particularly in respect of leachate management and gas enhancement – does not ultimately conflict with, and thereby prejudice, the need to maintain the integrity of the engineered structure. This highlights the need for the landfill scientist to work closely with the landfill engineer in order to achieve an acceptable degree of compatibility.

At the end of the day the principal aim should be the protection of the environment. There is no reason why, with careful design, this aim should not be achieved whilst at the same time optimising the benefit to be gained from collecting and harnessing a valuable resource in the form of landfill gas.

Leachate recirculation has tremendous benefits by reducing the strength of the leachate, especially with a very young leachate where the free-of-charge anaerobic digestion it receives in such a landfill as it percolates through the saturated layers is excellent pre-treatment.

Of course to achieve recirculation one actually has to have, if you like, a reservoir to pull on within the base of the landfill and therefore by definition one would have some standing leachate level there to pull on. The other point of course is another, in a sense, problem that is that of the hydraulics of heavily compacted waste at the bottom of a landfill, which is really quite impervious, and actually trying to get water to pass through such waste in a controlled manner is a tough one which neither the industry or its regulators have got to grips with yet.

Landfill reclamation in varies guises is becoming more popular in many areas. The most common form of landfill reclamation seldom gets reported is such, and it comprises the removal of waste from brownfield sites where old landfills were present. These are usually quite small tips, and quite often due to there age there are very few problems in moving them, into new lined areas. Odours that might have caused distress to neighbours are gone and it is simply a matter of clearing and cleaning the land for development, removing a constraint which would otherwise have prevented redevelopment of the land This may be either due to regulatory requirements or risks of foundation settlement, and/or possible landfill gas present.

Reclamation can make sense economically too, for shallow and very old landfills. In addition to raising the land value once it can again be used for development the continuing liability to the owner of any old landfill will also be reduced by reclamation. It is easy to forget that old landfill sites must be monitored on a regular basis to make sure they are not causing pollution and are safe from such matters as gas migration iot nearby houses and factories.

The responsibility for this monitoring rests with the local Environmental Protection Authority (Environment Agency England and Wales) (EPA/EA) and landfill operators themselves. Landfill gas removal diminishes the potential for landfill contaminants to travel as a gas and dissolve into the groundwater. The regulatory aim is always to protect the public’s health and safety from the potential for the landfill gases to concentrate in enclosed areas where harmful vapours could be inhaled or an explosive atmosphere could occur.

Landfill mining also achieves landfill reclamation and is carried out for a slightly different purpose. Landfill mining is all about recovering valuable metals, producing high quality fertiliser and retrieving construction materials. In some nations carrying out this sort of reclamation is used to make available real-estate that was once considered lost forever.

However, concerns arise about the release of landfill gas and odours during reclamation works. Landfill gas has an unpleasant odour that can cause headaches or nausea. The odour, however, is more irritating than a hazard to health as it can contain carcinogenic compounds. Landfill gas escapes should be monitored at least quarterly at agreed points around the site perimeter to check for migration. A gas collection system may be installed that will enable gas to be sucked out of the wastes and collected and the collected gas be converted into energy.

During landfill reclamation it has been reported that waste material has proved much harder to sort, and the actual productivity has been much lower than originally estimated in feasibility studies.

Gas Plasma technology is being sold to carry out landfill reclamation projects in the US, and the most favoured technologies will not require manual sorting. In gas plasma plants, waste material is fed into a specially designed chamber and the intense heat of the plasma breaks down organic molecules (such as oil, solvents, and paint) into their elemental atoms. In a carefully controlled process, these atoms recombine into harmless gases such as carbon dioxide. This is why gas plasma is described as a mass destruction method.

Landfill reclamation can remediate groundwater contamination problems. Groundwater moves slowly and continuously through the open spaces in soil and rock below ground. If a landfill contaminates groundwater, a plume of contamination will occur. Groundwater, surface water, soils and sediments ons ite become contaminated. In most cases, and routinely, monitoring wells have to be provided around landfills in areas likely to detect leakage (e.g., downstream of the groundwater flow).

It is a sad fact that in many countries environmental contamination from landfills is entering watercourses and underground aquifers at alarming rates. Liner breaches, if indeed the landfill was even lined to start, are not uncommon. Landfill reclamation can at as stroke return land to normal uses especially housing, and by placing the existing waste in a new environmentally sound landfill also remove pollution.

Space is becoming the biggest issue. We have little enough space in most cities already, so we can hardly afford to effectively sterilise land above landfills forever. Space is even seen as becoming increasingly scarce throughout the United States, particularly in the more densely populated urban and coastal areas. Old closed landfills as time goes on will eventually take up massive tracts of land, and the use of that land will be very limited unless extension reclamation of these old landfills can be carried out.

New MC3000 rolled out

Magpie Drilling has continued its expansion with a further MC3000 added to the drilling rig fleet. Following the increase in customer demand for deeper, larger diameter wells, with temporary and permanent steel casings, the need for increased power, higher torque, and superior depth capabilities are paramount.

The new machine has an extra rod in the carousel enabling it to drill 60m without any crew member ever having to handle a drill rod. A new design for the self extruding barrel has increased the power in which the pusher plate operates making the extrusion process faster and more efficient. More …

This summer was the second summer season, and the 4th stage of restoration capping at this Wexford County Council landfill during which Rowe Environmental provided capping construction quality assurance services.

The start of the works in June 2007 coincided with the uniqely heavy rainfall exprienced throughout the region that month. Although clay capping proceeded in between rain storms, problems arose with clay compaction due to the very waterlogged conditions on the landfill.

Civil Engineering Contractor Roadbridge used every opportunity to work whenever the site dried out in between rain showers, and the project was remarkable for not being not seriously delayed. This was despite the need for additional harrowing and recompaction of the clay over much of the site, in order to reduce the water content to acceptable levels, and the un-programmed addition of extra soils reinforcement to steep slopes within the restoration area.

The final stage of restoration capping at Killurin is programmed for next year when the recycling facilities and replacement residual waste landfill at the Council’s new Holmestown Landfill will be operational, and the Killurin Landfill closed.

The restoration capping works we completed this year
were similar to the Stage 3 of restoration which took place
through the summer of 2006.
Click on the image below to view
the Landfill Restoration slideshow for 2006:

 

The Waste Strategy 2007 has been published, and yes, of course, poor old landfill gets the “worst” (least preferred option) ranking in the waste heirarchy again!

Seriously though, there was never going to be any change to the requirements for landfills including the Construction Quality Assurance requirements for landfills, but we thought we would post this anyway!

Here is what Let’s Recyle have been saying about the Waste Strategy as far is it relates to landfills:-

Specific material type landfill bans on agenda
(24.05.07)

The first three chapters of Waste Strategy 2007 contain a number of key areas of interest including the suggestion of radical future approaches to the landfilling of biodegradable and recyclable waste.

Landfill bans
The document points to experiences on the Continent where a number of countries, such as Germany, France and Swdedn, have imposed strict bans on what can be landfilled.

The strategy said that Defra wil be “consulting, subject to further analysis, on the introduction of further restrictions on the landfilling of biodegradable wastes and recyclable materials.”

Explaining the thinking behind this, the strategy says that other EU states “have found that imposing legal restrictions on the types of waste that can be landfilled has encouraged higher rates of recycling and recovery.”

The Department also noted how these have been introduced with significant lead-times, as in Germany.

Hierarchy
The strategy repeats the waste hierarchy which has five levels. These are (the best) waste prevention; reuse; recycle/compost; energy recovery; disposal (the worst).

NORTHERN IRELAND INTERIM GUIDANCE ON LANDFILL CLOSURE: CAPPING AND RESTORATION:  The Environmental and Heritage Service haas released Interim Guidance on Landfill Closure: Capping and Restoration for EHS staff and operators. The procedures may be applied to both existing and new landfill sites. The guidance document sets out a brief overview of the main aspects to be considered when establishing the capping standards at landfill sites. More information here.