WHITEMOSS LANDFILL SITE

The Whitemoss Landfill owned and operated by J Routledge & Sons (Liverpool) Ltd has been in operation for the last ten years.

The site is located to the South of the M58, 500 metres West of Junction 4, on Whitemoss Road South, Skelmersdale. Junction 26 of the M6 is 6 km away and so the site is well connected to the Region's road network.

Skelmersdale lies to the North of the Motorway, whilst open fields predominate to the South, East and West; Liverpool is 15 km to the South West and Manchester 35 km to the East. Within 50 km of the site lie Lancashire and Cheshire, Merseyside and Greater Manchester. The site is located in the central part of the Mersey Belt, a major centre of manufacturing and commerce.

The site lies on a minor aquifer of intermediate vulnerability. It was formerly a worked out peat extraction partially backfilled construction waste landfill. Beneath the ground lies boulder clay of 8 m thickness, and beneath that mudstone.

A number of technical studies have been undertaken to accurately characterise the hydrogeology of the site and its surrounding area. A comprehensive report dated January 1997 was submitted to the Environment Agency (EA) and approved by them to demonstrate that the site when engineered to exacting design specifications would not have any unacceptable discharge of pollution at any stage in its life cycle.

Subsequently, the EC Groundwater, Landfill and in October 2000 Water Framework Directive were ratified. A further report was prepared and submitted in June 2003 to the EA "Groundwater & Surface Water Risk Assessment", which confirmed that the site complies with the most recent requirements of E U Law.

Many people are unaware of the care with which a modern landfill is constructed and operated. It is generally thought that a landfill merely comprises a hole in the ground, created either by natural contours or more usually former mineral workings.

In the case of Whitemoss as least this could not be further from the truth.

Firstly, the site was chosen for its location, rather than the chance of a pre-existing void. The geology and hydrogeology were extensively investigated before the decision was made to create the landfill. The geology and hydrogeology are exceptionally well suited to the purpose being a low risk ground water situation and the presence of boulder clay that is again exceptionally well suited in terms of its potential permeability and its engineering characteristics.

A demand locally for the minerals of clay and mudstone, for civil engineering and brick manufacture, complete a picture of a rare combination of factors.

The next part of the process of creating a landfill facility is to seek Planning Permission. A design was commissioned from a respected consultancy, Wardell Armstrong, studies undertaken, extensive discussions with the precursor of the EA, the regional Waste Regulation Authority and an Application submitted.

Once Planning Permission is obtained, a Waste Management Licence, now an IPPC Permit must be obtained. The EA agree the engineering details supplied by the Consulting Engineer. Once they are satisfied that a robust and effective lining and capping system will protect the environment, work can commence.

A Permit is produced which details the means by which ground and surface water will be protected long term, and the site managed to reduce the risk of nuisance or health risk to the human, and indeed animal population.

The permit holder must agree with the EA a means by which the future monitoring and restoration of the surface of the site after closure is financially secure.

The operator has to be declared as “Fit & Proper” to operate such a site and pass a series of twelve detailed assessments as to his competence carried out by external assessors. Each module examination comprise written and oral work, together with a portfolio of documented evidence further proving the ability of the candidate.

How is a Landfill Site constructed so as to ensure protection of the environment?

The lining system in the case of Whitemoss comprises a composite system of clay, High Density Polythene (HDPE) drainage systems and protection blankets.

A system of drains is created in the base below the lining system and where necessary the sides of the excavation. This is then led to a pumping chamber so that groundwater from outside of the excavation can be prevented from building up behind the composite line.

Calculations based on the tested physical characteristics of the clay determine the thickness of the clay liner. On site won clay is stockpiled. The stockpile is tested for its compliance with the specification as to particle size, density, moisture content and plasticity. Only material from the tested stockpile can be incorporated into the works.

A qualified engineer is selected and his c.v. assessed and approved by the E.A. He is employed by the third party Construction Quality Assurance Team. Every detail, at every step is pre-agreed by the E.A. and under third party Supervision, themselves audited by periodic visits by the E.A.’s own qualified engineers.

The clay is laid in 300mm layers. Each layer is tested on site by a Nuclear Test Gauge for density and moisture content. The clay must have an optimum moisture content of 12%. Less, and the particles won’t bind. More, and it loses mechanical strength.

The Nuclear Test Gauge is calibrated periodically (as required by E.A. guidance) by sand replacement tests conducted by another consultant. Similarly, Core Samples are sent for Laboratory Analysis for physical checks to ensure the emplaced clay meets the specification. The clay is rolled by a vibrating heavy self-propelled roller four times per layer.

Six layers were placed on the base of the excavation, between 2 and 3 on the side slopes, themselves constructed to a slope of 1 in 2.5 to millimetric accuracy. Survey by laser computerised equipment ensures the exact thickness of the layers.

A Specialist Company of flexible membrane liners and suppliers of HDPE is selected and engaged. The operatives are certified as being trained and competent in the welding of the HDPE.

Each roll is numbered and bears its own certificate of conformity from the manufacturer. Samples are taken from every fourth roll and sent for analysis as to thickness, plasticity, content of carbon black and other characteristics.

A trench is excavated at the top of the side slopes. The trench itself is to support the HDPE membrane and is designed to allow the liner to creep downwards slightly under the frictional pull of the weight of waste laid against it. This reduces the possibility of the HDPE liner being reduced in thickness by this downward pulling motion.

Each panel is then welded to its neighbour. This is achieved by a special self-propelled welding machine, which creates a double weld with a small air gap between the two welds. Once the weld is complete the air gap is filled with compressed air. A pressure gauge measures any drop in pressure, this proving if there is a leak. If a leak is detected then it is then located and a patch applied. An electrical conductor is incorporated within the hand weld so that the weld can be checked for water tightness.

All of this is supervised by the third party Construction Quality Assurance Engineer.
Finally the clay is in place, the under drainage connected and a drainage blanket and pipes are laid on top of the HDPE & drainage blanket. The drainage medium has to be chemically analysed, tested for its physical characteristics and laid under third party supervision.

The next step is that a further consultant is brought in – in our case from the Czech Republic to test the entire installation system.

Electrodes are placed beneath the HDPE and above in the drainage medium. A current is passed through and any leaks are detected, and remediated if necessary. The system is then re-checked.

All of the records, every weld test, every core sample result, survey of clay thickness, survey of every single panel and weld and a summary are incorporated into a report submitted by the Consulting Engineer to the Environment Agency. Details of laboratory test results on the leachate drainage blanket to ensure that the chosen medium has the correct chemical make-up, permeability and geotechnical properties are supplied before the drainage blanket is emplaced, under third party Construction Quality Assurance supervision.

A protective layer of geofabric is laid beneath the drainage medium, and appropriate laboratory tests to ensure its strength under the compressive effects of the waste undertaken to prove its resistance to penetration.

Once the drainage blanket, which extends up the sides, or batters, of the cell is in place then the first 1m layer of selected waste is emplaced. This waste is selected so as to exclude items such as long, hard, objects that could penetrate the protective layers of the liner below.

A site road is built to enable road vehicles to make the descent into the cell safely in all weather, ensuring that the vehicles tyres are protected from objects that could damage them, and that the vehicle stability is ensured.

Waste that meets the site licence (Permit) is laid in layers in such a way that it remains physically stable, enables precipitation to run through it for collection and treatment, and provides a safe working platform for machines and customers transport.

Whitemoss is permitted only for wastes that are classed as Hazardous. Although a waste stream may be classed as Hazardous under European and National Legislation, the actual risk posed may in fact be quite small. A television becomes "Hazardous" once it is discarded, though moments before it was sat happily in the corner of its owners lounge.

All wastes offered for disposal to Whitemoss have to comply with strict acceptance criteria. As would be expected, this excludes liquids, highly flammable, corrosive and oxidising wastes and Hospital or Clinical wastes. The criteria also place limits on the concentrations of substances within the waste to ensure the safety of people on, and off, the site, and to protect the environment.

In addition, all wastes to the site have to be pre-treated to meet EA requirements.

Boreholes into the waste extract Landfill Gas of flaring or energy recovery. Because of the nature of the waste at Whitemoss, little Landfill Gas is generated.

Rain falling onto the waste soaks through it to the collection system at the base of the site.

This water is then contaminated by contact with the waste. As the site is lined with a very impermeable liner, accumulation of liquid has to be carefully managed.

The liquid, known as leachate, is pumped via a purpose made well to a holding lagoon where it can be pre-treated if necessary before discharge to off-site treatment.

Once the cell has been filled to the levels agreed with the EA and Planning Authority then a similar procedure to that used to line the base and sides is adopted. An artificial liner is placed over a protection layer, and welded to the sides of the cell. A further mineral liner is laid over the top. Top soil is then placed on the mineral liner to protect it from desiccation and erosion.

Trees and other vegetation are then planted on the surface.

After the site has been capped monies set aside during its life into a special account accessible only for this purpose, are used to fund its monitoring and replacement of key management infrastructure (such as pipes, leachate treatment equipment etc).

In this way, once the waste management options of reduce, re-use, recycle have been exhausted the remaining residue can be disposed of safely. It should be noted that this is the Best Practicable Environmental Option recognised by all of the major Environment Campaign Groups.