SECTION C: How Do We Develop Guideline Values?
C.1 The overall approach
The principle of using guideline values is simple: we measure the level of ‘faecal indicator organisms’, which do not necessarily cause disease themselves but signal the potential presence of disease-causing organisms. Guideline values of faecal indicator organisms such as enterococci have been used successfully for a long time in recreational waters. However, there are still questions about the effectiveness of this approach for monitoring and measuring water quality, and a number of environmental and physical factors may influence the usefulness of faecal bacteria as indicators.
The main constraints to the approach used in current guidelines are as follows:
- Management actions are retrospective – they can be deployed only after human exposure to the hazard.
- While beaches may be designated as suitable or unsuitable for recreational activities, there is in fact a gradient of increasing severity, variety and frequency of health effects with increasing sewage pollution. It is therefore desirable to promote incremental improvements or prevention, prioritising ‘worst features’, to achieve cost-effective intervention.
- Although enterococci have been identified as having the best relationship with health effects in marine waters, they may also be derived from other than faecal sources in some conditions. [Such conditions as sub-tropical temperatures and the influence of mangrove swamps and freshwater run-off from dense vegetation have been identified in parts of New Zealand.]
- Many New Zealand recreational sites are at estuaries, where historical results from both Escherichia coli (E. coli) (as the preferred indicator for freshwater faecal contamination) and enterococci are required for an assessment of health risk.
Such constraints to the use of guideline values are not confined to New Zealand. In November 1998 a group of experts from the WHO, the Commission of the European Communities and the United States Environmental Protection Agency (USEPA) met in Annapolis, USA, to consider ways to address such anomalies and constraints. The experts agreed that an improved approach to regulating recreational water that better reflected health risk and provided enhanced scope for effective management intervention was necessary – and feasible. The resulting approach has become known as the ‘Annapolis Protocol’. Published in 1999, it covers approaches involving both an environmental hazard assessment and a microbiological water quality assessment.
See Note G(x) for further details on the Annapolis Protocol.
The Ministry for the Environment responded by establishing the Marine Bathing Working Group in 1999 as a consultation of interested parties to investigate the application of an ‘Annapolis’ approach to New Zealand conditions. The approach has been modified after consultation and trial during the 2001 bathing season. It has also been modified to incorporate updates from the WHO contained in their publications Bathing Water Quality and Human Health: Protection of the human environment water, sanitation and health (WHO 2001) and Guidelines for Safe Recreational Water Environments: Volume 1 Coastal and Freshwaters (WHO 2003), and as such is incorporated as part of these guidelines.
This approach has also been applied in the development of the freshwater guidelines, for which the Ministry for the Environment established the Freshwater Guidelines Advisory Group. The freshwater guidelines were trialled over the 2003 bathing season, and have been updated in light of feedback.
C.2 The framework
The framework used in these guidelines is a combination of catchment risk grading and single samples to assess suitability for recreation. This is a move away from the sole use of quantitative ‘guideline’ values of faecal indicator bacteria towards a qualitative ranking of faecal loading in a recreational water environment, supported by direct measurement of appropriate faecal indicators. The framework is summarised in Figure C1.
An explanation of all the features of this framework, including the Catchment Assessment Checklist (used to derive the Sanitary Inspection Category), the Microbiological Assessment Category and the Sanitary Inspection Category, will be given when we look in Part II at setting out to grade a beach. For the moment we are focusing on the final result of this process – the Suitability for Recreation Beach Grade.
This grade provides an indication of the general condition of a beach. The risk of becoming sick from swimming at a beach increases as the beach grading shifts from Very Good to Very Poor.
Conditions affecting water quality vary for the middle range of beach grades (Good, Fair and Poor). For example, ‘Good’ beaches usually comply with the guidelines, but events such as high rainfall increase the risk of contamination levels from run-off.
Weekly monitoring should be carried out during the bathing season for these middle-range beaches. For beaches where routine monitoring will be ongoing during the bathing season, the three-tier system applies, analogous to traffic lights:
- Highly likely to be uncontaminated (green):
‘suitable’ for bathing, but requiring water managers to continue surveillance (e.g. routine monitoring) - Potentially contaminated (amber):
‘potentially unsuitable’, requiring water managers to undertake further investigation to assess the suitability for recreation - Highly likely to be contaminated (red):
‘highly likely to be unsuitable’, requiring urgent action from water managers, such as public warnings.
The public will be informed when swimming is not recommended: for the marine guidelines, when two consecutive samples taken from the beach exceed the action level of the microbiological water-quality guidelines; and for freshwater, when one sample exceeds the action level.
See Note H(i) for information on sampling times and periods.
The grading process identifies sources of faecal contamination, such as sewer overflows caused by heavy rainfall, which influence the final Suitability for Recreation Grade. Contamination events may be triggered by specific conditions (e.g. rainfall). Where monitoring agencies can predict such contamination events, they may initiate management interventions to deter use of the site. Where these interventions can be demonstrated to be effective in discouraging use of the recreational site, the initial grade may be modified to reflect the usual water-quality conditions at that site. This is achieved by removing the source of the predictable exceedance events from the catchment assessment.
See Note H(xii) for more information on modifying beach grades.
We will now go on to look at putting this monitoring, grading and public warning system into practice.
Such modification of a grade, achieved by management practices, reflects the quality of water at the time of use. It does not alter the environmental conditions and microbiological data governing the initial grading.
