ATA research: The impact of greywater on domestic soil environments
During the last half of 2007, the ATA in conjunction with RMIT Environmental Science Department, undertook a soil analysis of seven surburban properties around Melbourne that have been using greywater on their gardens for a number of years. Sites were specifically selected on the basis of soil type, greywater reuse history and consistency of the water quality. Overall the investigation was designed to identify the major contaminants in soil after greywater application; determine if the greywater is affecting the soil’s physical and chemical characteristics; compare greywater applications on different soil types in different locations; and analyse the potential short and long term implications of continued greywater reuse.
The results of this project have shown that soil type and household chemical inputs are key factors in effectively managing greywater reuse. On clay soils, which are widespread across the Melbourne area, sodic waste-streams have altered the soil chemistry in some situations to the extent that drainage characteristics have been seriously affected which could potentially result in subsurface erosion and migration of wastewater to adjoining land.
In contrast, irrigation systems established on sandy textured soils showed only minor changes in soil chemistry. It was concluded that carefully managed irrigation strategies, including preparing heavy clay soils, combined with control of household chemical inputs are required for sustainable greywater reuse in domestic applications particularly on clay soils or soils with shallow clay subsoils.
It was also found that the design of the system is an important factor in ensuring even distribution of greywater to avoid any localised build up of chemical contaminants in subsoil’s. To observe the impact of greywater on soil chemistry several parameters were measured. They were: pH (water and calcium chloride), EC, soil moisture, soil classification (i.e. colour, texture), soil stability i.e. slaking and dispersion test (also wet dispersion), Major cations,CEC, SAR and ESP, Soluble salts, Phosphorus and Boron.
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