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XYZ Example - ERA Tier 1

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 Level 1 ERA process for XYZ Enterprises including problem identification, conceptualising a model of the site, a site investigation, receptor characterisation, exposure assessment, toxicity assessment, risk characterisation, and environmental risk management decisions. (Note: this is a long page).

For further details on the theory or background relevant to the particular stage in the ERA framework, click on the graphical icon beside the heading.

7B Anywhere Drive has been identified as a site requiring an ERA. 

Problem Identification should ‘take stock’ of the problem and determine what should be assessed. The site should be characterised, current and historic land uses should be determined, both at and around the site, and the contaminants of concern should be identified. Potential receptors should be defined and potential pathways identified.

The objectives for the ERA (including what information needs to be collected, analysed, or assessed) should be set and documented at this stage.  

Based on the information obtained from the preliminary site characterisation, an initial conceptual model for the site can be developed. This may be a simple site sketch, but it should identify possible contaminant sources, pathways and potential receptors.  It is also useful to tabulate the preliminary findings.  



XYZ Enterprises, Allsorts Industrial Park.

Current land uses:

Currently used as an industrial facility for the finishing of steel products and storage/sale of scrap metal. Around 60% of the site in bare soil, 20% with gravel chip surface cover, and 20% of the site with a concrete slab/building cover.

Historic land uses:

Based on the Certificate of Title and aerial photos, the land was originally pasture, and then developed by a sawmilling company as a timber processing yard. Building consents indicate that the site underwent upgrades. The date of timber treatment plant installation is uncertain but possibly from the early 1970s. The use of boron is uncertain but use of PCP is unlikely as a nearby site owned by the same company apparently undertook this task (see records for STU Ltd). Unconfirmed reports of a boiler and possibly an underground petrol storage tank (UST) at the site. Unconfirmed reports of waste dumping on the bank of the river.

Potential contaminants:

  • Copper, chromium, arsenic, boron,

  • Petroleum hydrocarbons, BTEX,

  • Metals (zinc, chrome, lead, others?).

Potential pathways:

  • Air – dust from wind action, traffic on site

  • Groundwater – leaching through soil profile, leaking from petrol UST

  • Surface water – stormwater runoff to river & drain, groundwater infiltration;

  • Leachate from dump,

  • Direct contact with dump materials.

Potential receptors:

River/drain biota, river/drain sediment, intertidal biota, riparian/ wetland biota, downstream river users, down-gradient groundwater users, upwind properties/residents, soil biota.

Site Investigation

At this point it is usually necessary to undertake some form of site investigation. In this example the site investigation involves some further inspection of the site and sampling and analysis of soils, sediment and surface water for contaminants of concern.

It is good practice to outline your site investigation in a site investigation plan so that you have a clear idea of what you want to investigate and how you want to go about your investigation before you start.

Many of the NZ guidance documents, reviewed as part of this project, have full discussions on site investigation methods. Some provide guidance on the number of samples that may be needed to provide a sound statistical basis from which to assess the extent of contamination. Australian Standard AS4482.1 – 1997 also provides details of these.

An example of a brief site investigation plan for on-site soil contamination for XYZ Enterprises is presented below.


XYZ Enterprises, Allsorts Industrial Park


To establish the presence/absence of Copper Chrome Arsenic Boron and trace metals contamination in soils at the site.

To undertake a site inspection to confirm the presence and location of underground storage tanks, waste dump, boiler ash previously identified.


Copper, chromium, arsenic, boron — ICPMS Timber Treatment Suite.

Sample Media:

On-site soils, off-site soil as control site

Sample Number:

7 on-site soil samples (n=21) & 1 off-site soil (background) (n=3) at 3 depths – 0.2m, 0.5m, & 1.0m.

Sample Locations:

On-site soil samples will be taken in a rough grid pattern; off-site soil (background) will be taken from the adjacent northwest farm paddock from at least 50m distance from the site boundary.


Chain of custody documentation for samples; photographs of the sample locations and other points of interest; update site layout map showing sample locations.


Sample results to determine the existence of on-site CCA/B & trace metal contamination.

Confirmation of location of UST dump site & boiler ash.

Other Points:

1: Possible excavation of test pits for dump site.

2: Test pits for UST &.Boiler ash.


What are the potential receptors that might be affected by the contaminants of concern?

In a level 1 assessment it is normally a straightforward procedure to identify and characterise on-site human receptors. While this process is not necessarily straightforward for ecological receptors, it is often sufficient to only broadly identify them. Relevant ecological benchmark criteria generally ensure the protection of sensitive species. However, despite this level of assurance, it is worth thinking about the range of ecological receptors that could be exposed to your contaminant of concern at an early stage in the risk assessment process.

For example soil biota may include plants, animals and fungi that may all be affected to a greater or lesser degree by soil contamination. Of the soil fauna, some may simply live in or on the soil, others may consume the soil or organic litter on the ground surface, and each may be exposed to a contaminant through a very different exposure pathway.

For the XYZ Enterprises site, possible receptors include:

Human receptors:

  • On-site workers & site visitors

  • Off-site residents downwind

  • Groundwater users; and

  • River and estuary users (e.g contact and non-contact recreation, fishers / mahinga kai) possibly affected through interaction with water and/or consumption of wildlife. To confirm or otherwise at a later stage.

Ecological Receptors:

Soil Biota: The site has been an industrial site since the 1960s. Soil biota assumed to be limited to common robust species with little off-site migration. Overgrown grass and weeds are present in places on-site and soil fauna and flora are of moderate concern as receptors.

Drain Biota:  Limited instream habitat, some weeds on bank, prolific algae. No fish or other fauna observed. Sprayed regularly by council staff. Sediment in-fauna, if present likely receptor.

Riparian (riverbank) Biota: The riverbanks are steep at this location. No apparent indigenous species or other riparian habitat of note (e.g blackberry). No receptors of concern.

Downwind Habitat: No apparent habitat of note downwind. Mainly industrial properties. No receptors identified.

ABC River:  ABC River as main receptor of concern. Include migrating fish, resident fish/eels, aquatic insects. Possible sediment in-fauna.

Wetland Biota:  450m downstream of the site includes raupo, reeds, willows, sedges, and waterfowl – ducks, occasional seagulls, rare bittern (DOC records), frogs, aquatic insects, eels. No receptors of immediate concern. Migration and/or feeding in and around site may require confirmation at level 2/3 if drain or river biota affected.

Intertidal Biota:  1.5km downstream of the site where river exists to sea via a channel. Narrow intertidal area on both sides of the channel. No known shellfish beds or other habitat of note. No receptors of immediate concern.


In summary, ecological receptors of immediate concern at XYZ Enterprises include:

  • Soil biota

  • Sediment infauna (drain and river)

  • Aquatic biota in the ABC River)

Wetland and intertidal biota are not identified as receptors of concern at this stage. They may need to be revisited later if adverse impacts are identified for aquatic biota in the ABC River (Risk Management Decision).


What concentrations of the contaminants of concern might the receptors be exposed to?

At level 1 the assessment of exposure is incorporated into the criteria against which you are assessing your contaminants of concern. These criteria have been developed for one or several potential exposure pathways and they may or may not be relevant to the conditions at your site.

For XYZ Enterprises four small examples are provided to highlight how exposure may be assessed.

Example 1 

Looks at how risks may be assessed at a Level 1 assessment by considering the appropriate exposure pathways for likely receptors.

Example 2

Provides a standard Level 1 assessment example for an area suspected of metals contamination. 

Example 3

Looks at how off-site aquatic effects can be identified and broadly scoped using on-site data.

Example 4

Looks at how other factors may affect a risk assessment.

What might the contaminants of concern do to the receptors and at what concentration? 

For a level 1 toxicity assessment the concentrations of contaminants of concern are compared with relevant guideline or assessment criteria for that contaminant. Again, the relevant guideline criteria tend to be conservative (i.e. they represent the likely worst case situation and therefore tend to be protective of most species). However, it is good practice to be aware of any factors that may change how the contaminant of concern affects your receptor. 

For example, some metals exhibit variable toxicity to aquatic life depending on the hardness of the receiving water. Others may exhibit different toxicity at different oxidation states and some organic compounds in aquatic environments can have increased toxic under sunlight. 

While these factors are generally well covered in the relevant guidance documents (reviewed in this site), summary tables or checklists often do not contain this information.  A good summary is presented in the MfE/MoH Health and Environmental Guidelines for selected Timber Treatment Chemicals 1997.

There are some instances where you may know very little about some of the basic properties of a contaminant of concern. Good sources of information on contaminants of concern can be found in various web-based databases (reviewed in this site).  These include iris, toxnet (http://toxnet.nlm.nih.gov/), or http://hazard.com/msds/

These databases can provide some of the basic information including its physical and chemical properties, likely human health effects and ecological effects. However, in many of these sites, the assessor could be presented with numerous benchmark criteria developed for different agencies for different purposes, some of which may not be suitable for use in all circumstances. 

For CCA and BTEX in soils we have compiled a list of some relevant benchmark criteria with a commentary on their applicability to NZ conditions.

XYZ Enterprise example - continued

Surface water samples were analysed from the river and drain at XYZ Enterprises and presented in the following table.

Average contaminant concentrations (n=3) from ABC river upstream (1R) and downstream (2R), of XYZ Enterprises and from drain upstream (1D) and downstream (2D) of XYZ Enterprises:





ANZECC (1992)
Copper 0.001 0.050 0.094 0.095 0.013 a

0.009 c

0.002 – 0.005 (h)
Chromium 0.005 0.006 0.004 0.012 0.016 a

0.011 c

Arsenic 0.008 0.009 0.025 0.042 0.340 a

0.150 c

Boron 0.064 0.692 0.004 0.978    
Nickel <0.0005 0.006 0.007 0.230 0.470 a

0.052 c

0.015 – 0.15 (h)
Zinc <0.001 0.095 0.260 0.491 0.120 a

0.120 c

0.005 – 0.05 (h)
Cadmium <0.0001 <0.0001 0.0003 0.002 0.0043 a

0.0022 c

0.0002 – 0.002 (h)
Antimony <0.0003 <0.0004 <0.0004 <0.0004   0.03
Lead <0.0002 <0.0003 0.0027 0.0059 0.065 a

0.0025 c

0.001 – 0.005 (h)
a: acute
c: chronic
h: hardness dependent

Total copper is elevated in river water downstream of the site and exceeds both chronic and acute criteria. The hardness of the water was not measured and although it exceeds USEPA criteria (at hardness of 100 mg/L) it is likely that water hardness in the ABC River could be much lower (30 mg/L) resulting in a lowering of the relevant criteria.

At this concentration, copper can be expected to be acutely and chronically toxic to aquatic organisms. However, its toxicity could be reduced if there is are elevated concentrations of dissolved organic carbon (USEPA 1999). Water hardness and dissolved organic carbon in particular will need to be measured to confirm this assessment.

Zinc is also elevated in the river water downstream of the site and exceeds ANZECC guideline values for the protection of aquatic ecosystems but not USEPA criteria. Further work would be required to assess the toxicity of zinc once the water hardness has been established.


A level 1 assessment of XYZ enterprises site at 7B Anywhere Drive has determined the following key points.

Receptor Toxicant Exposure
On-site worker TPH, BTEX. Soils exceed benchmark value for benzene only. Limiting pathway not complete. Likely secondary pathway (inhalation of benzene outdoors) meets benchmark criteria.
Site Visitor / On-site worker Physical contact with sharp materials at dump site Direct physical exposure to on-site workers and site visitors accessing site through broken fence.
On-site soil biota BTEX, Cu, Cr, As, Zn. Exceeds soil guidelines for Cu and Zn. Direct exposure through surface soils at concentrations exceeding benchmark criteria for Cu and Zn in soil.
Surface water ABC River: aquatic ecosystem Cu, Cr, As, Zn Exposure of aquatic species to Cu and Zn in surface water in ABC River in concentrations exceeds benchmark criteria.

At a level 1 assessment the degree of risk is usually expressed in qualitative terms. For example:

  • The risk to on-site worker from exposure to petroleum contaminants in the soil is likely to be low and within guideline values for likely site activities;
  • The physical risk to workers and visitors from contact with sharp material at the dump site is likely to be moderate as access to this area for site visitors is unrestricted and on-site workers are often working on the site dumping or re-using scrap material;
  • There is a potential risk to soil biota on-site and to aquatic life from elevated concentrations of Cu and Zn.
  • All other contaminants of concern are within guideline values for the protection of soil-biota and aquatic species.

The uncertainties of the investigation also need to be clearly outlined at this stage to provide a context to the Risk Characterisation. For the XYZ Enterprises there are several areas of uncertainty:

  • Recreational and cultural use of the ABC River has not been assessed at this stage;
  • The implications of exceedances of Cu and Zn on wetland and intertidal receptors downstream of the site are not addressed;
  • The toxicity of Cu in relationship to dissolved organic carbon has not been established.

One area of uncertainty is the source of the Cu and Zn. Previous examples routing soil contamination through to the ABC River suggested that the source of the contaminant at the site is limited. You may wish to check this to make sure that there are no other sources of Cu and Zn nearby (e.g. stormwater coming from upstream of the site).

There are also a variety of assumptions that also need to be recognised and documented. For example the migration of Cu and Zn from the site to the ABC River via groundwater is considered to be unlikely.


At this stage the assessor will need to make some decisions regarding management actions at the ABC site. These decisions may range from doing nothing, to undertaking a more detailed level of investigation and risk assessment through to remedying any adverse environmental effect that have been identified.

These decisions may be made by the site assessor, or they may involve consultation with a number of other parties, including the site owner, site users, regulatory agencies and/or those that could be affected by off-site effects such as neighbouring landowners, Tangata Whenua, or resource user groups.

For XYZ Enterprises, the following risk based decisions were made:

  • The dump site will be covered with a minimum thickness of 0.5m of compacted soil and the fence repaired to prevent access.
  • No further investigation or remedial work will be undertaken for petroleum contamination identified at the site. However, the presence of contaminants will be noted in site plans with an annotation attached to the plan that restricts building on that part of the site without further investigation or remediation.
  • The potential for Cu and Zn to affect soil biota will be further assessed.
  • The potential impacts of Zn and Cu exceedances on water quality in the ABC river will be assessed focussing on:
  • the nature of Cu and Zn discharges from the site and surrounding area;
  • factors that control toxicity of Cu and Zn to aquatic biota;
  • confirming the source of Cu and Zn;
  • identifying specific receptors that are present in the ABC River and assessing their sensitivity to Cu and Zn.

Assessing the potential for Cu and Zn to affect soil biota iterates a level 1 assessment using more detailed soil sampling and analysis.

Assessing the potential impacts of Cu and Zn on aquatic life in the ABC River is a level 2/3 assessment.

Where next?

If you are unable to make a conclusive decision, the next step is a Tier 2 assessment.  

This is beyond the scope of introductory risk assessment.  However, some details for the XYZ example at Tier 2 are provided.


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