WALO UK complete asphalt lining works at Westmill

Dense asphaltic concrete used to construct landfill barrier system at Biffa-operated site in Hertfordshire

WALO UK, specialists in hydraulic asphalt engineering, have completed another lining system at Westmill landfill site, near Ware, in Hertfordshire. Since 2003, the company has constructed a total of 10 cells at the site, with an overall capacity of around 2.5 cubic metres using dense asphaltic concrete (DAC).

The 38ha landfill site is located in a working sand and gravel pit and receives up to 350,000 tonnes of municipal waste from the south-east region annually. Situated on a chalk aquifer, Westmill is a particularly environmentally challenging site; for example the protection of the groundwater was of utmost importance when it came to selecting a lining system.

Using DAC, WALO have created a highly robust landfill barrier lining system that is impermeable to leachate and methane found in most solid waste landfill deposits. The latest lining system comprises a 300mm mineral attenuation layer, 200mm sub-base material layer, 60mm asphaltic binder layer, 80mm DAC layer and mastic seal coat to the base, side slopes and bund areas.

The project covered an area totalling 14,500 square metres and involved the hand placing of asphalt by paver and winch on a 30m slope. Following completion 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 quarries are dismissed as unsuitable for waste treatment as they have very steep walls. However, we have found that DAC is very stable on slopes even those as steep as 1:1.6, which means sites with very steep sides can be used for landfill. More space can be created for contained landfill while still providing great protection for the environment.

‘Our DAC is very strong yet flexible at only 340mm thick and has provided decades of impermeable sealing service in the waste-treatment industry.’