Resilient lining system installed at Westmill


Hydraulic asphalt specialist Walo UK has completed lining another cell with Dense Asphaltic Concrete (DAC) at Westmill Landfill site near Ware in Hertfordshire. This is the twelfth cell Walo has lined at the site with DAC since 2003.
The 38ha Westmill site is operated by Biffa Waste Services Ltd and receives municipal waste from the south east region of the UK. This is mainly waste from households and businesses, together with some construction industry waste. The site is located on a chalk aquifer and so environmental considerations are of paramount importance. Walo’s Dense Asphaltic Concrete (DAC) is resistant to chemical attack, impermeable to leachate and methane and will withstand years of use without risk of leakage or degradation, according to the firm. These qualities make it ideal for the complete containment of all materials that need to be impounded, such as landfill waste. Despite this impermeability, DAC is still very flexible and robust. This makes it particularly suitable for lining landfill as it can accommodate settlements of up to 10% (40 mm in 1000 mm) and yet traffic can run on it immediately after laying without causing any damage.

Cell size and shape
This latest cell to be lined at Westmill has a basal surface area of 17,300 m2, with slopes of 8,425 m2. The slopes are 65 metres long with a slope angle of 2:1. Walo also constructed two intercell bunds, measuring two metres high into adjacent existing asphalt lined. The asphalt was placed by hand on the intercell bunds and by paver and winch on the base and slopes.
The lining system comprises a 300mm mineral attenuation layer; a 200mm sub-base material layer, a 60mm Asphaltic Binder Layer (ABL); a 80mm DAC layer and a mastic seal coat to the base, side slopes and bund areas. Once the lining works were completed, a leachate collection and removal system was installed.
David Wilson, Managing Director of Walo UK Limited says: “Landfill cells of any shape and size can be accommodated using DAC. It provides a very strong but extremely thin lining system with the total thickness averaging around 340 mm, which saves significantly more void space compared to most other lining systems.”