Freshwater Protected Area Resourcbook

Appendix 21. Water quality guideines: a risk-based approach:

In the following text, wherever Guidelines is spelt with a capital ‘G’ reference is being made to the water quality guideline document (ANZECC & ARMCANZ 2000); wherever it has a lower case ‘g’ reference is made to a particular guideline level (trigger level) within the Guideline document. The discussion focuses on the environmental ‘value’ of ecosystem protection – other values such as potable water supply could have been used equally well in this example. The overview below is drawn from the more detailed explanation available in ANZECC & ARMCANZ (2000).

The first edition of the National Water Quality Guidelines (ANZECC 1992) included indicators for ecosystem protection. Two of the measures used in determining indicator levels related to biodiversity: that species richness not be altered, and that species composition remain similar to that of similar local, un-impacted systems.

When the NWQMS Guidelines were reviewed from 1996 to 1999 a new approach, focusing on ecologically-based management, was taken (Hart et al. 1999). The revision added three new dimensions to the guidelines, making them:

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  ecosystem-based (guidelines are ecosystem-specific as far as possible).
  
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  issue-based (guidelines focusing on problems caused by stressors rather than the individual indicators).
  
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  risk-based (the guidelines numbers are re-named ‘trigger values’ and a decision framework is proposed to assess the likelihood of adverse effects and the need for additional information).
  

Figure 1.0 demonstrates the general format of the hierarchical risk-based decision framework. A key feature to note is that the guideline trigger levels are equivalent to the single value guidelines of the earlier edition of the Guidelines. These guideline trigger levels represent the maximum ‘acceptable’ bioavailable concentration of a pollutant in the absence of site/ecosystem-specific information (the ‘default’ values).

Figure A21.0: Generic hierarchical decision framework for assessing physico-chemical stressors and toxicants in water or sediment:

To use the frameworks, the ambient concentration of a contaminant at a particular site is compared initially with the guideline trigger level. This initial measurement of ambient concentration may be a relatively simple, low cost measurement (e.g. total concentration). If the trigger level is not exceeded, the risk of an impact is regarded as low and no further action is required. However, if the trigger level is exceeded, there is some risk of an impact either occurring or having occurred. At this stage and if it is decided that no remedial action is to be taken yet, additional information on local environmental factors needs to be incorporated, and the trigger value adjusted through successive more complex steps. In the case of a proposed development, a prospective approach would be used.

At each step in the process, the ambient concentration is compared with the new guideline and decisions made on whether an impact is likely, and on whether the guideline should be modified further. The final guideline should, therefore, better reflect the real hazard to the particular ecosystem.
In general, each step through the decision framework becomes more resource intensive so that the user should consider costs versus benefits for each step. At any stage, the decision tree process can be concluded and the most recently modified trigger level applied as the guideline.
In using the hierarchical decision framework, it should be noted that, where there is no background information on a particular system to which the guidelines are to be applied, and no program in place for its acquisition, the precautionary approach is recommended: that is, to apply the guideline trigger levels (the conservative default values) as guidelines.
The Guidelines recognise six environmental values, and establish recommended guideline trigger values (eg: levels of concentration for the contaminant in question) for the first four of those values. The six recognised environmental values involve the protection of water quality for:

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  aquatic ecosystems (conservation levels 1 (high), 2 (medium) and 3 (low)),
  
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  primary industries,
  
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  recreation and aesthetics,
  
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  drinking water,
  
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  industrial water, and
  
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  cultural issues.
  

In summary, the process on which the Guidelines are built follows five consecutive logical steps as illustrated below:

This process is illustrated with the following hypothetical example relating to treated effluent from a piggery discharged into a high conservation value stream:

1. Define the PRIMARY MANAGEMENT AIMS, (including environmental values, management goals and level of protection). Simplified examples follow in boxes:

Aim: to maintain near-pristine ecological values in a defined river reach. Environmental value: protection of aquatic ecosystems. Ecosystem in question: upper perennial temperate riverine (derived from Queensland Wetland Inventory classification system). Issue in question: nutrient pollution. Environmental goal: to maintain or enhance the quality of the aquatic ecosystems in the river reach. Level of protection: to achieve the highest level of protection for high conservation / ecological value systems where management would be expected to ensure there is no change in biological diversity, relative to a suitable reference site condition.

2. Determine the appropriate WATER QUALITY GUIDELINES (tailored to local environmental conditions).

The ‘default’ values in the ANZECC/ARMCANZ Guideline document for total phosphorus and total nitrogen for freshwater aquatic ecosystems, for high conservation value are 0.04 mg/L and 0.008 mg/L respectively^14. These default values are not used in this case as specific studies have been carried out on this waterbody, in accordance with the risk-based approach set out in the guidelines. These studies have provided the following maximum levels: total phosphorus: 0.05 mg/L; total nitrogen: 0.01 mg/L defined from research applicable to the most sensitive components of the aquatic ecosystem in question. Pressure / response data are available for the ecosystem type and contaminants under consideration.

3. Define the ambient WATER QUALITY OBJECTIVES (specific water quality to be achieved) taking account of social, cultural, political and economic concerns where necessary.

Total phosphor us: 0.05 mg/L limit to be met by 90% of all samples; total nitrogen: 0.01 mg/L limit to be met by 80% of all samples, 0.03 mg/L limit to be met by all samples. If real-time monitoring is available, these would be re-defined as a percentage of total time. These are equivalent to target reference points. Limit reference points could be defined as total phosphorus exceeding 0.30 mg/L and/or total nitrogen exceeding 0.10 mg/L.

4. Establish a MONITORING AND ASSESSMENT PROGRAM (focused on water quality objectives) after defining acceptable performance.

5. Plan and implement an appropriate MANAGEMENT RESPONSE (based on attaining or maintaining water quality objectives). Actions necessary if objectives are not met need to be defined in advance – the decision rules.
Decision rules relating to effluent discharge from upstream piggery are defined. Effluent from the piggery undergoes routine storage and treatment before discharge to the river. Decision rule No.1: if either target reference point is exceeded, the licensed limit on discharge load must be reduced by 50% until water quality rises above the target levels. Decision rule No.2: if either limit reference point is exceeded, the discharge load must be reduced to zero, with all effluent to be trucked to alternative approved disposal.
More information on the NWQMS can be found at www.deh.gov.au.