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.

We will occasionally post capping design information on this blog. We hope that you will find these posts interesting.

To guarantee a landfill cap which will drain adequately and for effective gas collection, the landfill cap should incorporate a drainage layer above and preferably also, a gas collection layer below the cap’s low permeability lining system. 

The geosyntheic “Pozidrain” may be able to provide these functions with higher performance and lower cost than conventional crushed stone filters. The Pozidrain is also favoured by operators who want to squeeze the last once of waste into their landfill as the thickness of this material is much less than a stone layer, allowing more waste to be put in the landfill before the planning consented top of site levels are reached.

ABG Geosynthetics tell us that:

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 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. Pozidrain geocomposite drainage layer has a proven record in landfill capping.

If you are still wondering what Pozidrain material is, think of a very big area of a membrane material comprising many “egg boxes” joined together. Across the face remote from the low permeability landfill seal is “tack” welded a geotextile filter material. The egg box profile creates a continuous void which allows water penetrating the filter to drain away. A very simple but useful idea.

The Landfill CQA technician/supervisor must at all times ensure that the Pozidrain supplied meets the specified requirements, and is laid in accordance with the specification. This is likely to involve the checking, and acceptance of the contractor-provided supplier CQA records, plus some additional independent testing for verification of factory test data.

There will be a strong workload for landfill capping contractors this summer due to the closure of many landfills during 2006, which has taken place as a result of the ending of the grace period for the transition from Waste Management Licences to PPC Permits under the IPPC legislation.

Many landfill owners which did not apply for PPC Permits, and instead closed their sites, were able to keep them open until the end of the year, and even those closing earlier missed the summer (good weather) earthworks window for 2006. Therefore, they have been lining up their projects for this summer.

Landfill owners are required to cap and restore their sites under all legislation (old Waste Regulations and within their PPC permits) throughout Europe.

Although most savvy operators are actually sealing their sites as early as possible, and before capping, in order not to lose valuable landfill gas, which is utilised almost universally now (at larger sites) for power generation and the electricity revenue that provides.

Nevertheless, by permanently capping the site as soon as possible they provide themselves with the best permanent installation for leachate extraction at the earliest opportunity. Leachate collection from the gas wells will be minimised as soon as possible, minimising leachate generated, and reducing leachate disposal costs. At the same time the installed permanent leachate pumps will ensure maximum landfill gas yield by avoiding some wells being effectively blocked to gas production, by the presence of standing leachate.

For those. like Rowe Environmental, working in landfill Construction Quality Assurance, the summer also looks like being a very busy time.

Ken Rowe - Rowe Environmental