Internal Report 489
Supervising Scientist Division
Department of the Environment, Water, Heritage and the Arts, 2004
About the report
A report on the progress of reviewing the trigger values in Magela Creek, Gulungul Creek and Ngarradj (Iles 2003) was circulated to stakeholders for comment in late 2003. Written and verbal feedback from stakeholders on that report highlighted/reinforced the following important points.
- Because the trigger values for most parameters are based on a value that falls within the natural range of values at the reference site, it is expected that the triggers will be occasionally exceeded. In fact, the purpose of using values within the natural range is to draw attention to any potential change in water quality as soon it may be statistically noticeable. A single exceedance of a trigger based on reference site percentiles does not mean the value is outside the normal range of values and should not cause alarm or responses inappropriate to the event.
- Recognising the above point, there is a need to educate stakeholders and the public about the use of the trigger value system and appropriate reactions (management and stakeholder/public interpretations) to any exceedances.
- There is a need to interpret measurements with greater reference to the hydrological conditions at the time, especially for turbidity, which is highly variable across the hydrograph. Sampling of the reference site (and test site) has commonly occurred.