European Directives

Arguably, the most important European legislation relevant to landfill containment is embodied within the Council Directive of 17 December 1979 on the protection of groundwater against pollution caused by certain dangerous substances (80/68/EEC) (CEC 1979).

The Annex to this Directive contains two lists of generic as well as specific compounds or substances.

List I contains the most damaging substances and their direct discharge to groundwater, that is without percolation through an unsaturated zone, is prohibited. Indirect discharge of List I substances is permissible only where prior investigation shows the groundwater to be permanently unsuitable for other uses. Direct and indirect discharges of

List II substances may be authorised only after prior investigation and should be limited so as to avoid pollution of the groundwater by those substances (Article 3.2; CEC 1979). List II includes, amongst others, ammoniacal nitrogen (NH3-N), and it must be assumed that Article 3.2 would encompass landfill leachates, since this constituent is singularly the most long lived and potentially problematical gross component of landfill generated liquors.

The severity of the Directive is mitigated by two factors:

Groundwater (Article 1.2(a); CEC 1979) is understood to be water that is below the surface in a zone of saturation, implying that indirect discharge through an unsaturated zone, in which attenuating processes remove the
polluting potential, is acceptable;

An exemption is made (Article 2(b); CEC 1979) for discharges that contain substances in lists I and II in a quantity or concentration so small as to obviate any present or future danger of deterioration in the quality of the receiving
water.

Taken together, these Articles suggest that controlled release of contaminants is permissible, so long as it is by indirect discharge and that attenuation in the unsaturated zone protects the groundwater.

More recently, a proposal for a Council Directive on the landfill of waste (91/C 190/01), submitted to the Commission on 23 April 1991 tightened the provisions of the Groundwater Directive by laying down landfill containment criteria irrespective of site specific conditions and knowledge of attenuation mechanisms.

Annex I (Section of the draft Directive requires that, with the exception of landfills for inert wastes only, the following containment criteria must be met, either by the presence of in situ natural strata, or to the same level of hydraulic containment by engineering measures (synthetic liners or amended soils):

• minimum thickness of 3 metres;
• maximum hydraulic conductivity of 1 x 10^-9 m sec.

For engineered liners in clay the thickness is normally 1 metre, minimum at a maximum hydraulic conductivity of 1 x 10^-9 m sec.

See also http://www.geofabrics.com/docs/UK_Environment_Agency_regulation_15.pdf

Disclaimer: This post is provided for educational purposes only. Readers must not rely on this information for landfill design projects, or any use where reliance is placed on the accuracy of this information. This page may not be updated. ALWAYS refer to the up to regulations issued by the local regulator. Use of this site is prohibited for any use in connection with compliance with regulations.

The often proposed alternative landfill liner system to Low Permeability Clay Layer or HDPE Lining Membrane consists of replacing the default design of compacted clay liner (CCL) with a Geosynthetic Clay Liner (GCL).

There are currently two major types of commercially available GCLs. One type consists of bentonite encased between two geotextile fabrics and the second type consists of bentonite glued to a HDPE geomembrane.

The type of clay typically used in GCLs is sodium bentonite. Sodium bentonite is the name given to the highly plastic clay mineral montmorillonite, with sodium as the primary exchangeable cation.

Bentonites used to fabricate GCLs are processed in an unhydrated state such that they appear to have a granular consistency. However, upon hydration with water, the bentonite swells to form a continuous clay layer.

GCLs are shipped in rolls typically 3.7 to 5.3 meters wide and 25 to 60 meters long. They are installed by unrolling to form panels. Adjacent panels are overlapped, and for some products, powdered bentonite is placed between the panels at overlaps.

Large-scale laboratory testing has shown that, when installed in accordance with the manufacturer’s specifications, GCL overlaps are self-sealing and do not create a preferential pathway for liquid flow.

GCLs have been used in liner systems and cover systems for landfills, surface impoundments, and tank farms, as well as in other structures. When used in landfills, GCLs are often substituted for the compacted low-permeability soil component of a composite liner. The function of the GCL in the composite liner is identical to that of a compacted soil liner, which is to provide a low-permeability barrier to liquid flow through any defect in the overlying geomembrane.

The GCL material is manufactured under strict quality control (QC) guidelines. The QC requirements include conducting index and performance testing on both the supplied materials and finished product at specified frequencies. After the material is approved at the manufacturing plant, care is taken to keep the rolls dry, not stack them too high, and keep them from damage during handling.

Prior to acceptance in the field, information concerning the manufacturer’s name, product name, lot and roll number, and length, width, and weight must be submitted to the on-site CQA representative, who will verify all records.

To analyze the leakage through a composite liner utilizing a GCL instead of a CCL, D’Arcy’s equation is utilized based upon an assumed design hydraulic head over the liner.

The leakage through a membrane liner has been found to be closely correlated with the hole defects. In a recent paper a defect size per acre of 1 cm2 was assumed, however assessments of defects and their likely frequency and size vary widely.

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.

Leachate drainage layers are necessary in most waste landfill sites to minimise the accumulation of leachate within the site and they reduce the risk of contamination of surrounding ground and groundwater. A cheaper and environmentally preferable option is be the use of scrap vehicle tyres, but is their use permissible and what happens to them under pressure? A paper in the proceedings of Waste 2004 by A.P. Hudson, R.P. Beavan, and W. Powrie helps us to understand this.

Normally layers of whole or shredded tyres exhibit excellent drainage properties, but if tyres are used as the main drainage layer at the base of a landfill the concern exists that they may compress under the overburden stress from the weight of the waste above and cease to act as an effective drainage layer.

The results of a series of tests undertaken by the University of Southampton are reported by the above researchers as presented in their paper examining the compressibility and changes in hydrogeological properties of shredded and whole tyres subjected to a range of stresses typical of landfill conditions.

In the UK over 400,000 tonnes of used vehicle tyres are produced each year (Hird et al. 2002). The problem of disposing of used tyres has been made worse by the EU Landfill Directive which prohibited the disposal of whole used vehicle tyres to new landfills from 16 July 2003. The disposal of shredded tyres to landfill will be banned on 16 July 2006. There is, therefore, a need to establish alternative methods of re-use, materials/energy recovery and disposal of tyres.

The Landfill Directive permits used tyres to be utilised as engineering material in landfills. Use of whole or shredded tyres are often a cheaper and environmentally beneficial alternative to aggregates for the construction of landfill drainage layers or trenches. However drainage layers at the base of landfills will be subjected to high overburden stresses from waste subsequently placed above.

There is little published research indicating i) the extent to which tyre drainage layers will compress under such stresses, ii) the reduction in hydraulic conductivity due to compression and iii) the effect of tyre shred size on the compressibility and hydraulic conductivity of tyre layers. However, these atters have been addressed in their paper in a large scale compression cell in order to investigate the above.

The data demonstrated that tyre layers will compress under stress and this will result in a reduction of drainable porosity and hydraulic conductivity. The construction of any leachate drainage layer using whole or shredded tyres within a landfill would need to take into account the compressive behaviour of the material under load.

Countries that have specified a minimum hydraulic conductivity for landfill drainage layers generally give values of between 1 x 10^-3 and 1 x 10^-4 m/s.

However, this group found that shredded tyres would easily comply with requirements as low as 1 x 10^-3 m/s at stresses up to 600 kPa, but would only meet the most stringent requirements of some nations at stresses below 400 kPa.

The data presented in this paper demonstrate that the hydrogeological properties of whole and shredded tyres change according to the applied stress. In general the data indicates that shredded tyres are suitable for use as a drainage medium in landfill applications.

Dense Asphaltic Concrete has been as a Landfill Lining membrane material for many years and although it is not commonly seen in the UK, it is used much more often in Europe, and particularly in Germany.

The Dense Asphaltic Concrete is formulated in a manner which ensures both very low permeability and possibly as low as 1 x 10^-11 m/s, and permeability to landfill gas is also lower than for clays.

This is an imporant point as the ability of clays to pass some methane gas is often overlooked for single clay liner designs. Let us not forget either that the primary motivation for the composite lining (clay/HDPE)systems which are the norm now throughout the British Isles, was originally the concerns about landfill gas movement through the clay membrane. It happens also to be far less likely that a pinhole in the HDPE will ever leak when in a composite arrangement that hole will be backed up by the clay geomembrane layer.

Asphaltic concrete is stable on steeper slopes than HDPE unless special measures are taken to support and/or reinforce the HDPE, and much less prone to the sort of slip plane development we often see between HDPE and clay and sand/HDPE on slopes and banking.

Another big assett when considering this alternative lining material is its robustness during the infilling of the first layer of waste. All CQA Engineers worth the name will have experienced HDPE lining damage which occurs when the top 300mm of leachate drianage stone is being emplaced, and then potentially can occur again when the compactor vehicle runs in with the first waste lift.

Resistivity checks completed once the leachate drainage stone over the membrane often identify small holes in the HDPE liner after the leachate stone has been spread and levelled. These tend to be caused by a moments lack of concentration which the driver may suffer. Unfortunaelty, one unfortunate jab downwords (as the backactor spreads the sand or gravel of the leachate drain over the HDPE geomembrane) can be all that it needs to created minor pin holes, and to see about a dozen occurring per hectare was not uncommon in CQA Reports, a few years ago.

A UK specialist contractor offering Dense Asphaltic Concrete in the UK is WALO UK. http://www.walo.co.uk/

Dense Asphaltic Concrete can be an extremely versatile product, suitable for many types of applications.

The ancient civilizations of Egypt, Babylon and Assyria all used bituminous lining materials and mortars for waterproofing and building, some more than 5,000 years ago, and many examples of their work remains intact even today.

More recently with the advances in hydraulic technology, asphalt has been shown to be an effective material for sealing Dams, Reservoirs, Canals, Water Catchments, Sea Defences, Coastal Groins, River banks and importantly for us - Landfill Sites.

WALO is a main UK supplier.

Although the following topic is not directly a landfill CQA issue we thought that it would be of real interest to many of our readers.

Compulsory site waste management plans (SWMPs) for construction projects over £300,000 in value, have been a legal requirement in England since April 2008, and are therefore needed for landfill works contracts. The intention is that the plans will forecast all waste produced on site and how much will be recovered or disposed of.

The SWMP should help businesses manage construction waste as part of a project rather than an afterthought. By planning for construction waste much earlier than has been the practice it should be possible to do much better in managing construction waste. Early experience that has been reported has suggested that in building projects it has been possible to achieve substantial savings which exceed the costs of producing and updating the site waste management plan.

A landfill site lining development or surface restoration project is undeniably a construction project, and almost all will exceed the threshold cost. Therefore, each project will need a site waste management plan, which starts with the designer and becomes the responsibility of the principal contractors on commencement of the work on site.

The regulations set out a range of offences relating to the failure to produce or implement a plan, punishable by a fine of up to £50,000 on summary conviction, or an unlimited fine on conviction on indictment.

On these landfill projects there will be little if any construction waste produced at all, apart from possibly some spoilt or unsuitable material, and the usual site facilities wastes. As ever, these otherwise laudable regulations make little sense in some applications, and in landfill in our view, we have such an example.

So how does a landfill contractor set about writing his site waste management plan after being awarded the contract and receiving the client’s design stage plan, for a landfill project?

What should the SWMP contain?

According to NetRegs, the level of detail that your SWMP should contain depends on the estimated build cost, excluding VAT. Their summary suggests the following:-

For projects estimated at between £300,000 and £500,000 (excluding VAT) the SWMP should contain details of the:

• types of waste removed from the site
• identity of the person who removed the waste
• site that the waste is taken to.

For projects estimated at over £500,000 (excluding VAT) the SWMP should contain details of the:

• types of waste removed from the site
• identity of the person who removed the waste and their waste carrier registration number
• a description of the waste
• site that the waste was taken to
• environmental permit or exemption held by the site where the material is taken.

At the end of the project, you must review the plan and record the reasons for any differences between the plan and what actually happened.

The contractor, or anyone else exporting waste from the site must still comply with the duty of care for waste.  However, because it will now be necessary to record all waste movements in one document, having a SWMP will help the site contractor’s management to ensure they comply with the duty of care.

For help in preparing your SWMP see the video on the Site Waste Management Plan hub page, or  Landfill Site Waste Management Plan page.

The use of a Geosynthetic Clay Liner (GCL) as the low permeability layer in landfill lining systems and restoration caps can provide a cost effective and readily Construction Quality Controlled alternative to natural clay. In fact this material may be the only option in regions where the local geology is such that no clay of suitable quality is available.

A GCL uses Sodium Bentonite, a dehydrated clay that has long been recognised as an ideal impermeable barrier material, and which will expand once in the soil to six or more times its initial volume.
Claymat is an example of this type of product which comprises a sandwich of bentonite between two layers of geotextile. The result is a thin, flexible (it arrives in rolls, clean, easily transported and installed) lining system. Finesse Claymat is as manufactured by ABG of Meltham, and there are a number of other manufacturers.

Layers of sand or fine gravel (150 to 300 mm) are often placed on top and/or below the GCL as specified by the landfill capping system designer to protect it from damage during installation or thereafter.

The GCL membranes on the market have been tested to provide both an excellent self-healing capability, and chemical resistance, and are accepted by most environmental regulators. A paper available from Thomas Telford Journals shows that permeability can be compromised if suitable treatment is not applied at overlaps, so clearly the CQA Engineer will need to take care about ensuring good site procedures on this matter. (See “Forensic analysis of excessive leakage from lagoons lined with a composite GCL”, At Thomas Telford Journals.)

Assessments of the environmental protection afforded by a landfill liner require that all underlying soil and geosynthetics components are considered in landfill contaminant migration assessments. The results described in a 2004 paper provides published data for laboratory GCL diffusion and sorption coefficients, required to perform contaminant migration assessments for five VOC contaminants commonly found in municipal solid waste leachate. Assessment of diffusion coefficients and clay-leachate compatibility assessment is also deemed necessary to ensure acceptable long-term performance. In fact GCL membranes were shown to give permeabilities generally significantly lower than those reported in the literature for compacted clay liner materials.

Pozidrain ground water drainage membrane is also often used in conjunction with a Geosynthetic Clay Liner as when laid above the GCL it reduces the hydraulic head and stress on the geomembrane and it also provides additional physical protection against puncture.

A significant number of landfill sites have already utilised the benefits of Geosynthetic Clay Liners and many use Pozidrain and equivalent products within these systems.

SITA Cornwall  News (January 2008) – reports: Improvement in compliance… Landfill

SITA Cornwall’s two landfill sites play an important role in managing the county’s waste. A great deal of work was carried out in 2007 at the landfills and even more is planned for 2008.

It was a busy year in terms of engineering at United Mines Landfill in 2007, with the construction of a new landfill cell, the diversion of a sewer and surface water system and the capping of an area of 600m2. The leachate plants at both United Mines and Connon Bridge sites were refurbished which assisted the significant reduction of leachate levels.

Local residents and councillors have joined a community liaison group at United Mines to discuss issues around the site and preparations have begun for an open day in spring.

The aim to cap a large area of United Mines and Connon Bridge confirms that major landfill construction will continue in 2008.

2008 will also see the temporary closure of the Connon Bridge Landfill site. Work has already commenced to improve the visual impact, increase gas and odour control and further reduce leachate generation.

Efforts will also be concentrated on reducing the sites’ impacts both on the local and global environment, with the development of a strategy to reduce the sites’ water and energy use.

(Clearly there will be plenty of Landfill CQA work in the region this year – Ed.)

This is a question for our expert visitors.

The answer is: “Leakage Detection Layers”. We have quoted some text from a US landfill lining systems report.

“The double-composite liner system, …, consists of a primary liner overlaying a secondary liner with a leak detection layer between the two liners. Both the primary and secondary liners have two low permeable components. The leak detection layer is a layer between the two liners. The purpose of the leak detection layer is monitor the performance of the upper liner and allow appropriate action to be taken when leachate is found in this layer. This liner system has a leachate collection system directly above the primary liner.”

Just why the idea never took off in Europe is the next question. It has been suggested to your BlogMaster that the presence of the leak detection layer introduces an additional weakness, and this is probably the reason why it is disliked outside the US. After all, if the leak detection layer becomes contaminated the leachate in it might find a hole anywhere across the base to escape through due to the ability for it to flow through the detection layer material itself.

Also the theory has it that to spend equal money due to the cost of the detection layer, on Landfill CQA is a much better investment, after all the landfill owner will be monitoring outside the landfill for any escape of leachate, in any case, as a matter of good practice, so the leakage detection layer isn’t essential to detect any leak.

Continue to use the “comment” link below, and tell us what you think about the cross-atlantic differences in approach here. We would be delighted to see you views.