Temporal and spatial distribution patterns of heavy metals in soil at a long-standing sewage farm.

Australia's oldest sewage farm in Werribee, Victoria is a significant public asset with more than 110 years of history and it now treats half of Melbourne's municipal sewage. Currently three parallel methods, i.e. lagoon, land filtration and grass filtration were used to treat raw sewage from Melbourne. The land filtration area is soil-pasture-cattle complex system and it operates on 3,633 ha of permanent pastures for livestock grazing. The land filtration area by intermittent irrigation of sewage occurs during the months of high evaporation from October to April. The monitoring study was aimed to find out the temporal and spatial distribution patterns of heavy metals in the soil at land filtration area in the long standing sewage farm. The monitoring results show that the temporal distribution patterns of Cd, Cr, Cu, Ni, Pb and Zn follow the exponential regression equations in soil layer 0-20 cm and the linear equations in soil layer 20-40 cm respectively. The accumulated concentrations of heavy metals in the soils are high enough for the land to be considered contaminated. The exponential trend of heavy metal of soil in land filtration area should be controlled immediately by soil remediation or by change of treatment process of flow configuration.