DESIGN METHODS FOR THE DEVELOPMENT OF WASTE-WATER LAND DISPOSAL SYSTEMS

Recent changes in legislation governing water quality management of receiving water bodies have led to a reappraisal of wastewater land disposal techniques. However, more stringent regulations have also necessitated the development of a multi-disciplinary planning approach, to ensure that land based wastewater disposal is functionally and environmentally sustainable in the long-term. Of principal concern are the long term impact of nutrients, salt and other potential contaminants on the soils of the receiving site and on downstream water quality. Assessment of hydrological, soil physical and geological characteristics, together with civil construction and service considerations, assist in the determination of receiving site selection, application area and balance storage volume, irrigation method, environmental monitoring system specification etc. Analysis and interpretation of wastewater and soil chemical characteristics determines the pre-application water treatment required, and allows long-term monitoring of the effect of wastewater disposal on the receiving-site soils. Two case-studies are presented. One describes the planning and design of a recently commissioned land-disposal system using industrial wastewater from a chemical process plant to irrigate a Eucalypt plantation in western metropolitan Melbourne. The other reports on the on-going assessment and planning of a large-scale land-disposal system proposed to accommodate the treated sewage effluent from a large north-west Victorian regional city.