Predicting the site water balance of a phytocapped landfill site using HYDRUS 1D

An alternative landfill capping technique known as ‘Phytocapping’ (establishment of perennial plants on a layer of soil placed over the waste) was trailed in Rockhampton, Australia. In this technique, trees were used as ‘bio-pumps’ and ‘rainfall interceptors’ and soil cover as ‘storage’ of water. The environmental performance of the phytocapping system was measured based on its ability to minimise water percolation into the waste. The percolation rate was modelled using HYDRUS 1D for two main scenarios (with and without vegetation) for the thick and thin caps respectively with the measured values. Four different combinations of transpiration and canopy rainfall interception for thick and thin phytocaps were also used to check the credibility of the phytocaps o restrict water percolation through the waste. Results from the modelling using actual figures showed percolation rates of 16.7 mm yr-1 in thick cover and 23.8 mm yr-1 in thin cover, both of which are markedly lower than those expected from a clay cap. Furthermore, results from modelling using the four combination also showed < 70 mm yr-1 percolation, which is less than 10% of the total rainfall (780 mm yr-1), received in Rockhampton. All scenario point to one direction; stating the credibility of phytocaps to restrict water percolation in to the buried waste.