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XYZ Example - ERA Tier 2

What is a contaminated site?

Who does what?

Why is it important?

What is risk management?

Risk assessment fundamentals

Risk assessment methods

Limitations of risk assessment

What are RA tiers?


Problem Identification

Receptor Characterisation

Exposure Assessment

Toxicity Assessment

Risk Characterisation

RM Decisions

Project Initiation

ERA Tier 1

ERA Tier 2 (Advanced)

ERA Tier 3 (Advanced)






In this page we take you through the whole Tier 2 ERA process for XYZ Enterprises including problem identification, refining the conceptual site model, receptor characterisation, exposure assessment, toxicity assessment, risk characterisation, environmental risk management decisions.

At tier 2 you may need to look at site specific factors that would modify the guidelines values or benchmark criteria you are working with.

Based on the findings of the tier 1 ERA, the assessor should be able to refine the conceptual model for the site.

This should include the aspects of the site that the assessor wishes to investigate, including contaminants, pathways, potential receptors and areas or aspects of the site that are still uncertain (e.g. wetland and intertidal biota as ecological receptors and recreational and cultural users as receptors).

The objectives for this tier of ERA should follow from the Risk Characterisation and Risk Management Decisions steps previously undertaken.

The amount of information that needs to be collected at this tier could increase dramatically. The assessor may need to prioritise what aspects of the site require investigation.

For example, assessing factors that control the toxicity of Cu and Zn in surface water (toxicity assessment) may resolve potential issues regarding potential effects on aquatic biota with little additional work.

For XYZ Enterprises the main objective at this tier is to determine whether Cu and Zn discharging from the site is affecting aquatic biota by assessing:

  • contaminant pathways; and
  • factors that may control Cu and Zn toxicity.


Receptor characterisation involves the identification of potential receptors more thoroughly to allow for a fuller identification what species may be present and of these, which may be potential receptors.

For the ABC River potential aquatic receptors could include:

River Biota

Aquatic Invertebrates:

  • Based on regional council data;
  • Mainly fly and midge larvae, snails, worms and some cased caddis (Oxyethira spp.) in shaded bankside vegetation;
  • Mayflies and stoneflies rare;
  • Macroinvertebrate community affected by high sediment load and lack of riparian/river bottom habitat.


  • From Fish & Game Council information;
  • Short and long finned eels present throughout this reach, probably a population permanently resident as well as those migrating;
  • Small populations of rainbow trout present upstream, migrating populations may be exposed to contaminants;
  • Inanga (Galaxias) migrate upstream but only very small numbers (anecdotal);
  • Mullet through tidal reaches
  • Likely to also be introduced fish: catfish known, bullies and mosquito fish likely, but not considered significant populations of concern.

At this stage, if there is some concern on aquatic effects in downstream habitat it may be prudent to identify and characterise these receptors also. For example:

Wetland biota:

  • From DOC data when the reserve was last surveyed 1987.
  • Aquatic insects similar to river with addition of mosquito larvae, and a number of backswimmers (water boatmen);
  • Fish, mainly eels and bullies;
  • Common tadpoles/frogs present in open water;
  • Birds: large population of mallard ducks, some grey ducks noted, resident during breeding season, fewer at other times. Small population (25-30 individuals) of Australasian bittern. Not normally known this far south, so considered by DOC to be a population of note and justify active protection measures. Diet includes insects, small fish, frogs/tadpoles and small eels. Population appears stable, but preliminary studies indicate the reserve could support twice the number of individuals.

Other factors that could impact on the receptors but are unrelated to the site need to be considered. For example, the absence of a particular invertebrate species in the river could be a result of poor habitat quality rather than the toxicological effects of the contaminants of concern.


At tier 2 considerably more detailed investigation on contaminant exposure pathways is required. This may involve further work in identifying pathways and assessing what mechanisms (e.g dilution, attenuation) may increase or decrease the potential for exposure of a receptor to a particular contaminant. Wherever possible incomplete pathways should be documented.

For the XYZ Enterprises site it may be necessary to establish runoff characteristics for the site so that mass loadings of contaminants to the ABC River can be assessed, or available dilution in receiving waters of the ABC River during run-off events can be calculated.

A stormwater runoff model analysing rainfall intensity, infilltration, evaporation, surface roughness (depression storage) and runoff may need to be developed to assess what amount of run-off could be generated from particular storm events. Better assessment of stormwater flow in the drain may be necessary to assess the degree of dilution that could be afforded by the drain prior to discharging into the ABC River.

You may also want to assess how representative your original samples are. For example, do the samples collected represent locally elevated concentrations before full mixing in the ABC River is achieved?

You may also want to confirm how the contaminants are transported off-site. Are they as metals bound to sediment or largely as dissolved species? If they are bound to sediment, are they being remobilised from sediment in the drain?


At tier 2 a full evaluation of the toxicity of the contaminants of concern may be necessary. For Cu and Zn as our contaminants of concern, this could include a detailed assessment of the factors that could reduce or modify the toxicity of these metals, for example:

  • pH
  • the presence of dissolved organic carbon; and/or
  • water hardness;

There is now very good supporting documentation providing a comprehensive support and background information used to develop guideline values or benchmark criteria (e.g. ANZECC 2000) and databases (reviewed in this site) where published physical, chemical, toxicological properties of contaminants are summarised. These include iris, toxnet (http://toxnet.nlm.nih.gov/), or http://hazard.com/msds/
This data should be reviewed.


Risk characterisation should identify and fully discuss the factors that may modify the exposure of the receptors to the contaminants of concern. This will most likely involve a more detailed analysis of exposure pathways, factors that may control the toxicity of the contaminant, and the relevance of the benchmark criteria to the particular receptors of concern.

The risk is still most likely to be described in qualitative or semi-quantitative terms such as:

Cu concentrations exceed benchmark criteria for the protection of aquatic life. However, the absence of sensitive cladoceran species in the ABC River suggests that the guideline value is overly conservative for this site. In the absence of this species, Cu concentrations fall below that likely to be acutely toxic to identified aquatic biota.


The risk management decisions that are made at this tier should follow-on from the risk characterisation as outlined for tier 1.

At this tier of assessment the impacts are likely to be more than minor. In addition, any remedial measures that are proposed could result in unacceptable impacts on the environment.

Where next?

If you are unable to make a conclusive decision, the next step is a Tier 3 assessment.  

Some details for the XYZ example at Tier 3 are provided.


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Page last updated: 01 May 2007

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