NHMRC opens consultation on draft ADWG updates for ammonia, nickel, and chlorate

NHMRC opens consultation on draft ADWG updates for ammonia, nickel, and chlorate: implications for Australian contaminated land practice

Proposed Changes to ADWG Parameters and Impact on Site Assessment

In April 2026, the National Health and Medical Research Council (NHMRC) opened a public consultation period on proposed updates to three chemical parameters within the Australian Drinking Water Guidelines (ADWG): ammonia, nickel, and chlorate. Submissions close on 5 June 2026. The proposed changes include a significant relaxation of the health-based guideline value for nickel (from 0.02 mg/L to 0.05 mg/L), the retention of an aesthetic-based limit for ammonia with an explicit confirmation that no health-based guideline value is required, and the introduction of a new health-based guideline value for chlorate set at 0.8 mg/L. These changes follow the monumental 2025 regulatory cycle that delivered PFAS NEMP 3.0 and sweeping ADWG updates for per- and polyfluoroalkyl substances, indicating that the NHMRC’s rolling review programme is operating at an accelerated pace.

For water utilities, these proposed changes are directly operational. For contaminated land professionals, environmental auditors, hydrogeologists, and their clients, however, the significance is equally profound but less immediately obvious. Under the National Environment Protection (Assessment of Site Contamination) Measure 2013 (ASC NEPM 2013), the ADWG provides the statutory basis for Tier 1 Groundwater Investigation Levels (GILs) applicable to drinking water receptors. Any revision to ADWG values flows directly into the numeric thresholds used to assess whether groundwater contamination at a site constitutes a potential risk to human health. A site that currently triggers exceedance of a nickel GIL may not do so once the updated guideline takes effect, while sites with chlorate groundwater detections that previously lacked a formal health-based benchmark will now be assessed against a defined threshold.

Developers, legal counsel, and local councils managing contaminated land or reviewing planning certificates should treat this consultation as an early-warning signal. Environmental due diligence reports, remediation action plans (RAPs), and site audit statements prepared in the next 12 to 24 months will need to explicitly address whether the GILs applied are based on the current ADWG or the forthcoming revised version, and what the distinction means for site risk characterisation and remediation endpoints.

Key details of the proposed ADWG changes

The proposed revision to the nickel health-based guideline is the most consequential of the three updates for contaminated land practitioners. The NHMRC is proposing to raise the permissible concentration of nickel in drinking water from 0.02 mg/L (20 µg/L) to 0.05 mg/L (50 µg/L). This represents a 150 per cent increase in the allowable concentration and directly reflects a comprehensive review of updated toxicological evidence. The NHMRC’s draft states: “Based on health considerations, the concentration of nickel in drinking water should not exceed 0.05 mg/L.” At sites where nickel is a contaminant of potential concern (COPC) in groundwater, particularly those associated with former industrial operations, electroplating facilities, battery manufacturing, or geogenic nickel-bearing geology, this revision will alter the comparative assessment of measured groundwater concentrations against the applicable GIL. For sites currently in assessment or remediation, this could affect the remediation target, the waste classification of excavated material, or the basis of a current or pending site audit statement.

The ammonia update is less disruptive from a risk assessment standpoint but remains relevant to sites where ammonia is monitored as an indicator of landfill leachate, sewer exfiltration, or agricultural impacts on groundwater. The NHMRC draft proposes retaining the aesthetic-based guideline of 0.5 mg/L (measured as ammonia), noting that this value relates to the corrosion of copper pipes and fittings rather than direct toxicity. The draft explicitly confirms: “No health-based guideline value is set for ammonia.” This means assessors cannot apply a health-based GIL for ammonia under the ASC NEPM 2013 Tier 1 framework. Any risk characterisation for ammonia must rely on aesthetic or odour-based thresholds, or on site-specific Tier 2 or Tier 3 risk assessment where receptor pathways and exposure assumptions are explicitly modelled.

The chlorate update introduces a new health-based benchmark where none previously existed in a formalised ADWG context. The proposed guideline value is 0.8 mg/L. The NHMRC draft states: “Based on health considerations, the concentration of chlorate in drinking water should not exceed 0.8 mg/L. Action to reduce the formation of chlorite and chlorate is encouraged, but must not compromise disinfection, as non-disinfected water poses significantly greater risk.” Chlorate enters the environment primarily as a disinfection byproduct from water treatment, but it is also generated by industrial bleaching processes and has been used historically in herbicide and defoliant formulations. At sites with legacy industrial bleaching, pulp and paper processing, or agricultural chemical storage histories, chlorate in groundwater may now become a newly defined COPC where it was previously unquantified against a health benchmark. Practitioners who have not been routinely including chlorate in groundwater analytical suites should review whether it warrants inclusion based on site history.

It is important to note that these are draft guideline values subject to public consultation closing 5 June 2026. They have not yet been formally adopted. The NHMRC may revise values, accept submissions recommending further review, or confirm the proposed values following the consultation period. The timing of any formal adoption and subsequent incorporation into site assessment frameworks will depend on the outcomes of that process.

References and related sources

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Published: 27 Apr 2026

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