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Recycling of wastewater is important for achieving sustainable use of water in both urban and rural areas. Currently, in Australia, there are strict regulations on disposal and reuse of wastewater. Irrigation of sporting fields is one of the most common applications of wastewater recycling. However, there is an increased risk of soil salinity in the vadose zone when recycled water is used for irrigation. This is due to the generally increased levels of salt in the recycled water compared to that of town water supply. This paper presents salt transport modelling for a sporting oval (Greygums Oval) in Western Sydney which has been irrigated with recycled water for more than four years. The modelling was carried out for 1277 days using HYDRUS 1D, which is a one dimensional salt transport model. Meteorological data was used to specify atmospheric boundary conditions, which was collected from nearest weather station of Penrith Lakes, 4 km from the Greygums Oval. Average total dissolved solids (TDS) of recycled water varied in the range of 480-630 mg/L. Hydraulic loading rate and salt loading of applied irrigation water were 160 mm/year and 713 kg/ha/year, respectively.

The results of salt transport modelling of recycled water for irrigation showed a 77% increase (from 0.38 g/L to 0.67 g/L) in the root zone soil water TDS concentration over the period of 1277 days. However, during the simulation period, predicted TDS concentration showed significant fluctuations, which can be attributed to the influence of rainfall on soil water content and the movement of salt within the rootzone. The increasing trend was supported by a limited number of field data points. The field data collected generally supported the findings of the model. However, more field data are required to validate the model.

The results also indicate that weather conditions, particularly rainfall, appear to have significant impact on the accumulation of salt in the soil. That is, accumulation of salt in the soil due to recycled water applications can be more critical in the arid than in the tropical rainforest climatic conditions. For arid regions, due to limited availability of water, there is an increased pressure for using recycled water for irrigation. The results of this study appear to indicate that, if the recycled water is applied indiscriminately, the soils in this region may be under severe risk of salinization. However, further studies are required to quantify the risk of salinisation.