What is a
Why is it important?
What is risk management?
of risk assessment
What are RA tiers?
A risk management decision should be derived directly from the Risk
Characterisation based on the question:
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).
the Risk Characterisation indicate that adverse effects to receptors are
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
Of these methods, risk management goals generally fall into three
- Public protection measures,
- Containment techniques, and
- Physical and chemical clean up techniques.
Of the latter two, the options generally include one or a combination
- Collection and removal,
- Insitu containment,
- 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
- 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
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:
- Minimise toxicity
- Control lateral movement of
- Prevent/reduce infiltrating rainfall
upward migration of contaminants/gases
- Ongoing maintenance requirements.
- Horizontal subsurface barriers - jet grouting, chemical 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
- Soil vapour extraction / soil venting
- Steam extraction
- Chemical oxidation
- Soil flushing
- Soil washing
- Solvent extraction
- Insitu bioremediation -
bioaugmentation or biostimulation
- Biopiles /
- Excavation & disposal
- Soil mixing
Clean-up Technologies - Groundwater/Surface water:
- Air stripping
- Air sparging
- Spray irrigation
- Chemical oxidation / UV
- Insitu bioremediation
- Free product recovery - pump,
skim, recovery trenches/drains
- Ion exchange
- Membrane filtration
- Pump & treatment - pH adjustment, chemical
addition, settling, filtration, ion exchange, electrodialysis, reverse
- Pump & disposal
- Natural attenuation
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
- do nothing
Other factors that may affect a risk
management decision will require consideration. These may include:
- policies and objectives of the relevant regulatory
- 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
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
There are a variety of reasons for documenting the RA process,
- describe how the RA was conducted
- provide evidence of a systematic approach to each aspect of the
- 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.