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Risk Management Decisions

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





A risk management decision should be derived directly from the Risk Characterisation based on the question: 

'Does the Risk Characterisation indicate that adverse effects to receptors are likely?'  

The ultimate goal of risk management is to select a socially and environmentally acceptable and cost effective strategy that mitigates the threats to, and provides protection for, human health, welfare and the environment as well as allowing, where possible, flexibility in future land uses (ANZECC 1992).

While there are a wide range of risk management options available, based on Source-Pathway-Receptor methodology, potential contamination risks to human health and the environment can generally be resolved in one of three possible ways:

  • Source reduction - isolation, removal or treatment of source contaminants to reduce or eliminate contamination. 
  • Path manipulation - use of mechanisms such as barriers to prevent contaminants moving off site. 
  • Receptor removal - preventing receptors coming into contact with contaminants.

Of these methods, risk management goals generally fall into three broad categories:

  • Public protection measures, 
  • Containment techniques, and 
  • Physical and chemical clean up techniques.

Of the latter two, the options generally include one or a combination of: 

  • Collection and removal, 
  • Insitu containment, 
  • Insitu treatment, and 
  • Removal and treatment/destruction.

Selection of appropriate risk management options should be made only after determining all the necessary information including: 

  • Contamination type 
  • Chemical and physical properties of the contaminant 
  • Site specific geology and hydrogeology 
  • Extent (depth, width, length, speed) of contamination 
  • Clean-up targets - how clean will it be, what are the likely future land uses 
  • Effectiveness of clean-up technology - all contaminants simultaneously or different methods for different contaminants, characteristics of mechanism used 
  • Suitable disposal of residuals from remediation process 
  • Likely costs to achieve clean-up targets

Public protection measures: 

  • Reduce site access - particularly for physical hazard and air emissions. 
  • Source prevention/reduction - preventing further contamination. 
  • Minimise exposure pathways - preventing movement of contaminants or use of a contaminated area

Containment Technologies: 

These methods principally involve mechanisms of containment without the excavation of material to prevent migration of contamination and eliminate exposure pathways. Effective containment can be a comparatively cheap option but ongoing site management and information issues must be addressed.

  • Surface capping - clean cover technology, must address: 
    • Safe permanent barrier 
    • Minimise toxicity 
    • Control lateral movement of infiltrated rainfall 
    • Prevent/reduce infiltrating rainfall 
    • Control upward migration of contaminants/gases 
    • Resist subsidence/settlement/erosion/slope instability 
    • Prevent/reduce combustion risks 
    • Ongoing maintenance requirements.
  • Horizontal subsurface barriers - jet grouting, chemical grouting, claquage grouting 
  • Vertical barriers - slurry trench cutoff walls, grout curtains, sheet piling, high density polyethylene (HDPE), other impermeable or semi-permeable liner material.

Clean-up Technologies - Soil: 

  • Thermal destruction/incineration 
  • Thermal desorption 
  • Solidification / stabilisation 
  • Vitrification 
  • Soil vapour extraction / soil venting 
  • Steam extraction 
  • Dehalogenation 
  • Chemical oxidation 
  • Soil flushing 
  • Soil washing 
  • Solvent extraction 
  • Bioremediation 
  • Insitu bioremediation - bioaugmentation or biostimulation 
  • Landfarming 
  • Biopiles / biospheres 
  • Excavation & disposal 
  • Soil mixing 
  • Natural attenuation 
  • Degradation

Clean-up Technologies - Groundwater/Surface water: 

  • Containment 
  • Air stripping 
  • Air sparging 
  • Adsorption 
  • Spray irrigation 
  • Biofilm 
  • Chemical oxidation / UV 
  • Dehalogenation 
  • Insitu bioremediation 
  • Free product recovery - pump, skim, recovery trenches/drains 
  • Precipitation 
  • Ion exchange 
  • Membrane filtration 
  • Pump & treatment - pH adjustment, chemical addition, settling, filtration, ion exchange, electrodialysis, reverse osmosis 
  • Pump & disposal 
  • Natural attenuation 
  • Degradation

At all tiers, risk management decisions should take into account not only the effect of continued exposure of the receptor to a contaminant, but also the potential effects of any remedial action proposed. 

Risk management decision tasks

Making a Risk Management Decision entails deciding which of a variety of options are the most appropriate to manage the site. These options typically include:

  • do nothing
  • monitoring
  • prevention
  • remediation
  • decommissioning.

Other factors that may affect a risk management decision will require consideration.  These may include:

  • policies and objectives of the relevant regulatory agency
  • community expectations
  • perceived risk
  • costs of remedial or other actions
  • benefit of those actions.

The Australian and New Zealand Guidelines for the assessment and management of contaminated sites provides a good discussion of factors likely to affect a risk management decision.


At each stage of the RA, the process should be documented. This will most likely involve the collation of the information into a report. 

The most important components of reporting include outlining the objectives of the study, the methods used, and results obtained, the uncertainties and assumptions on which these were based, the risk characterisation conclusions, and the risk management decisions taken. 

The report should provide interested parties with sufficient information to understand why each decision was made throughout the process. You may choose to prepare a report at each Tier of RA undertaken, or generate mini-reports for each task, to be collated into a site report to inform the risk management decision.

There are a variety of reasons for documenting the RA process, including to:

  • describe how the RA was conducted
  • provide evidence of a systematic approach to each aspect of the RA
  • provide justification for the methods used and decisions taken including the risk management options chosen
  • provide an accountability mechanism
  • continuing monitoring and review of risk management actions
  • share and communicate information.

Tier 1 documentation may include a technical report outlining the basic site information obtained during Initiation and Tier 1 investigations, including contaminant concentrations, potential transport mechanisms and pathways, potential receptors, and benchmark criteria used to determine the acceptance levels for on-site contamination. This report should also outline the Risk Characterisation conclusions, the risk management decision made and, where appropriate, the terms of reference for the Tier 2 RA.

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Page last updated: 01 May 2007

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