Monday 22 December 2008

The Use of Landfill Tyre Drainage Layers

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?

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.

Schredding Scrap Tyres - watch this video!



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. 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 Landfill Directive permits used tyres to be utilised as engineering material in landfills.

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.

The data demonstrated that tyre layers will compress under stress and this will result in a reduction of drainable porosity and hydraulic conductivity.

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.

Therefore, by adding some more specification paramaters and sizes, it has been possible for the recycling industry from now on to produce anew (UK) tyre bale product which will serve a market in the secondary materials / recycling arena.
Steve Evans has provided more leading information on Landfill use of recycled Tyre Drainage layers at his blog. A full version of this article is available at Shredded Recycled Tyres.

How to Design a Permanent Geological Exposure in a Landfill

One of the most common locations for landfills are worked out quarries and quarries suitable for landfill are an increasingly valuable resource for this reason.

In a growing number of cases suitable sites include rare geological exposures of mineral bearing rock, or strata of regional importance which need to be kept exposed after landfilling for educational and also often for historical reasons.

Watch Our Video About a US Landfill



These SSI's can result in conflict between conservation and waste disposal interests.

Where quarries used for waste disposal contain Sites of Special Scientific Interest, it is necessary to maintain safe long term access to the geological exposure.

However, it is possible to minimise the conflict and to provide for these geological SSI's without undue difficulty, as we will describe.

The following list of considerations is broadly based on research described funded by the Nature Conservancy Council in the early 1990s, and has led to the identification of engineering measures designed to optimise landfill void in quarries whilst protecting, in the long term, geological Sites of Special Scientific Interest.

To provide long term, safe, unhindered access to the geological exposure with minimal sterilisation of landfill void space for waste, it is necessary to provide an engineered structure which limits land-take and which maintains a safe and secure perimeter barrier to the waste material.

The presence of a geological exposure in a quarry used as a landfill may have a significant effect on the design and operation of the landfill particularly with respect to leachate management.

Natural drainage should be provided where possible to prevent the accumulation of surface water adjacent to the geological exposure. Where this is not possible or the base of the geological exposure is below the water table, pumping may be necessary to facilitate access to the exposure.

It may be necessary to take measures to prevent the movement of leachate from the landfill site through or beneath the waste retaining structure towards the Site of Special Scientific Interest where it may contaminate accumulating surface and groundwater.

Landfill gas is flammable, is explosive if ignited in an enclosed space, and can also create an asphyxiating atmosphere. In Europe gas hazard sites (such as landfills) are controlled by the ATEX Directive and national regulations, such as the UK's Dangerous Substances and Explosive Atmospheres Regulations.

Where the landfill perimeter slopes adjacent to the geological exposure are engineered and graded to a profile of less than 1:3 access by visitors on foot across mown ground should present no significant problems if all visitors wear suitable footwear.

However, if the above criteria are met, there is no reason why a geological SSI and a landfill cannot co-exist without a significant conflict of interest.
Steve Evans has provided more leading information on Landfill CQA (landfill Construction Quality Assurance) at his blog. A full version of this article is available at Permanent Geological Exposure in a Landfill UK.