Understanding point source and non-point source pollution
Pollutants enter the water environment from two main classes of inputs.
Point sources
These are the readily identifiable inputs where waste is discharged to the receiving waters from a pipe or drain. Most industrial wastes are discharged to rivers and the sea in this way. With few exceptions, most point source waste discharges, are controlled by EPA through a works approval and licensing system. The licence for each input specifies the quality and quantity of the waste permitted to be discharged to a river, lake or the sea at a particular location.
State environment protection policies (SEPPs) require these licences be drawn up in such a way that water quality objectives for the receiving waters are met. This often requires industries and other waste discharges to treat their wastes to remove pollutants before discharging to the environment.
Waste discharge licences are legal documents. If the levels of pollutants in the waste or the quantity of waste discharged exceeds the limits set down in the licence, the person or company responsible for that discharge can be prosecuted by law. EPA staff inspect waste discharges from time to time and take samples of effluent which can be analysed to determine whether the licence is being met. The issuing and enforcement of licences for industrial waste discharges has been important in improving the quality of Melbourne's streams and Port Phillip Bay and also in waterways in other parts of Victoria.
Now that industrial and sewage waste discharges are effectively controlled by works approvals and licensing, 'point source' inputs are contributing less to pollution problems in Victoria. EPA is now directing attention to the other main category of inputs, like 'non-point sources'.
Non-point sources
Non-point sources of pollution refer to those inputs which occur over a wide area and are associated with particular land uses, as opposed to individual point source discharges.
Urban land use
In some outer-urban and urban fringe areas, a reticulated sewerage system is not available so sewage is discharged to septic tanks. Seepage and surface runoff of septic tank effluents are major forms of non-point source pollution of streams in these areas.
Other forms of non-point source pollution in urban areas include rainfall runoff from street surfaces contaminated with car oil, lead from petrol, dust and the faeces of animals and soil and sediment runoff from construction sites.
Agricultural land use
In farming areas non-point sources of pollution include pesticides, fertilisers, animal manure and soil washed into streams in rainfall runoff. Where stock are given access to stream banks they may foul the water and accelerate erosion.
Forestry land use
Forestry operations may contribute to non-point source pollution of streams by increasing soil erosion and sediment runoff.
Non-point source pollution is often more difficult to control than point source pollution. In urban areas the provision of reticulated sewerage systems and adequate street cleaning are important measures, while in farming and forestry areas, soil conservation practices and the controlled application of pesticides and fertilisers are necessary if pollution of waterways is to be avoided.