Phytocapping of Landfills

Phytocapping presents a sustainable alternative to the conventional top barrier cover design. It relies on the capacity of a porous substrate (usually of locally available soil) to store water together with the natural processes of surface evaporation and plant transpiration to remove the stored water as a means of controlling water ingress into the landfill. This chapter is based on the Australian experience in researching and implementing phytocaps as final covers for municipal waste landfills. In 2006, the Australian Alternative Cover Assessment Program (A-ACAP) was established to compare the performance (in terms of drainage, landfill gas, and plant growth) of phytocapping against traditional compacted clay barrier caps. The trials showed that phytocapping has the potential to reduce drainage as effectively as compacted clay barrier caps and in a more predictable manner; to oxidize fugitive methane emissions more effectively than barrier caps; and to enable more variable and sustainable vegetation communities to be established. Guidelines published as an outcome of the A-ACAP have been adopted in Australia as a basis for design and are being referenced in regulatory guidance as they are reviewed and updated. Phytocapping has now been approved and constructed in all mainland States (with the exception of Western Australia, where construction is due to commence shortly). The full-scale experience has shown that phytocapping is an alternative to conventional barrier caps but requires specialized input into design and different techniques for construction and maintenance to ensure its continued performance.