Articles & Case Studies


Posted: Thursday 30th May 2013

Hydraulic asphalt engineering experts WALO UK have completed the tenth cell at Westmill Landfill site, operated by Biffa Waste Services Ltd. Since 2003 WALO UK has constructed a total of ten cells, with an overall capacity of around 2.5 million cubic metres at Westmill using Dense Asphaltic Concrete (DAC).

The 38 hectare Westmill site is located in a working sand and gravel pit near Ware in Hertfordshire and every year receives up to 350,000 tonnes of municipal waste from the south east region of the UK. Being located on a chalk aquifer, Westmill is a particularly environmentally challenging site; protection of the groundwater was of the utmost importance when it came to selecting a lining system. Using DAC, WALO has created a highly robust landfill barrier lining system, which is impermeable to leachate and methane, found in most solid waste landfill deposits.

The lining system of the tenth cell, totalling 14,500m2, comprised a 300mm mineral attenuation layer; a 200mm sub-base material layer, a 60mm asphaltic binder layer; a 80mm DAC layer and a mastic seal coat to the base, side slopes and bund areas. The works involved the hand placing of asphalt on 450m of intercell bund and the placing of asphalt by paver and winch on a 30m slope. Following completing of the lining works, a leachate collection and removal system was installed.

David Wilson, Managing Director of WALO UK Ltd, said:

“Our particular speciality is in providing impermeable barrier systems for a large range of applications, and landfill is a key area of our expertise. On projects such as Westmill, where environmental sensitivity is of paramount importance, our DAC is the ideal engineering solution, while also remaining cost effective for our clients.

“Many potential sites, such as old quarries, are dismissed as unsuitable for waste treatment as they have very steep walls. However, we have found that our DAC is very stable on slopes, even those as steep as 1:1.6, which means even sites with very steep sides can be used for landfill. This means more space can be created for contained landfill while still providing great protection for the environment. Very strong – yet very flexible – our DAC is only 340mm thick and provides decades of impermeable sealing service in the waste treatment industry.

John Orchard, Engineering Manager, Landfill & Treatment Division, Biffa Waste Services Ltd, said:

“Biffa has worked with WALO UK for over nine years and I personally have worked with them for two years. WALO UK takes a positive, consultative approach to its work with Biffa and has always provided cost effective, high quality technical solutions to our engineering needs. We look forward to continuing our relationship with WALO UK in the years to come.”

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