Predicting site water balance of a phytocapped landfill site using Hydrus 1D model

Municipal Solid Waste (MSW) generation is a threat to the environment frommodern living. In Australia, up to 95% of the waste is placed in landfills at par with the global statistics. Landfills mostly contain putrescible wastes that cause environmental hazards due to leachate generation and methane gas emission. Irrespective of the stringent guidelines and new technologies for reducing these impacts, many landfills in Australia are barely equipped because they are expensive and not feasible for small and medium sized landfills. Various types of capping systems are also promoted as a postclosure remedy for completed landfills to isolate the buried waste from outside environment, mainly water. Environmental Protection Agency (EPA) in Australia has prescribed the use of clay caps to minimise percolation of water into the waste. Clay caps on the other hand are often found to fail over longer term due to cracking and do not allow optimal interaction of methane with oxygen, which is a must for methane oxidation. Hence a new technology called „Phytocapping‟ was trialled in; Rockhampton, Australia using 21 different tree species over two different soil depths (viz. Thin cap; 700mm and Thick cap; 1400 mm). The percolation rate was measured using HYDRUS 1D software for two different scenarios (with and without vegetation) for the thick and thin caps respectively. Results from modelling clearly demonstrate the importance of the type of vegetation in a phytocap. Results also suggest that a thick cap (570 mm) has better water retention capacity than a thin cap (330 mm). Similarly, simulations incorporating15 years meteorological data showed lower percolation rates (16.7 mm yr-1) for thick cap than thin cap (23.8 mm yr-1).