William Chirgwin

William Chirgwin

William Chirgwin, NSW Office of Environment and Heritage, Science Division, Water Wetlands and Coasts Science Branch.

Operationalising the Australian Water Quality Guidelines in New South Wales, Australia

In 2018, the Australian Water Quality Guidelines (AWQG) were updated to reflect improved understanding and increased community interest in waterway health. This included updating default guideline values (GVs) for water quality and focusing on developing and applying locally relevant and site-specific GVs for fresh and marine water quality to support more accurate water quality assessments.

One methodology the AWQG provides for developing site-specific GVs (SSGVs), calculates GVs based on a percentile calculation of appropriate reference site data (80th/20th percentile, 90th/10th for disturbed waterways). While this technique has a successful record developing SSGVs, limited guidance exists surrounding its application, especially in highly disturbed waterways, where developing SSGVs is more challenging.

This study aims to develop a rules-based framework governing the application of reference data based SSGVs, including data requirements and applicability for waterways with different levels of protection.

Water quality data from across NSW will be aggregated and a representative group of waterways identified with ongoing monitoring programs and appropriate reference sites. Multiple SSGVs will then be generated for indicators at each site, categorised by percentile calculated, number of reference sites used, and the temporal extent of reference data.

SSGV appropriateness, defined as an accurate representation of non-adverse levels of variance from natural conditions, will be determined based on site data exceedance rates, assessing exceedance rates for appropriateness based on site condition, and comparative performance relative to AWQG default GVs. This analysis will support a comparison of SSGVs to identify the method’s data requirements and assess the method’s applicability across sites with different levels of protection.

The SSGV comparison is expected to illustrate specific minimum data requirements for generating appropriate SSGVs using this method. It is also expected that highly disturbed waterways and systems will not be conducive to this method, necessitating the use of an effects-based SSGV calculation.

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