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
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
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
- 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:
- 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
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:
- 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
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:
- 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)
physical, chemical, toxicological properties of contaminants are summarised.
These include iris, toxnet (http://toxnet.nlm.nih.gov/), or
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
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.
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.