CRC CARE Technical Report 13 - hard copy
Australia has no current guidance on the field assessment of volatile compounds for sites where vapours have the potential to migrate into buildings and pose risks to human health. There are recommendations to provide such national guidance. This report updates knowledge available internationally related to guidance and methods of vapour assessment. It is intended to be used with other documentation to inform the variation of the Australian National Environment Protection (Assessment of Site Contamination) Measure (NEPM) currently underway.
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Australia has no current guidance on the field assessment of volatile
compounds for sites where vapours have the potential to migrate into
buildings and pose risks to human health. There are recommendations to
provide such national guidance. This report updates knowledge available
internationally related to guidance and methods of vapour assessment. It
is intended to be used with other documentation to inform the variation
of the Australian National Environment Protection (Assessment of Site
Contamination) Measure (NEPM) currently underway.
Australia
has no current guidance on the field assessment of volatile compounds for sites
where vapours have the potential to migrate into buildings and pose risks to
human health. There are recommendations to provide such national guidance. This
report updates knowledge available internationally related to guidance and
methods of vapour assessment. It is intended to be used with other
documentation to inform the variation of the Australian National Environment Protection (Assessment of Site Contamination)
Measure (NEPM) currently underway.
In this report:
- the processes underlying vapour behaviour are
described
- available guidance is reviewed
- a framework for vapour assessment and screening
is suggested
- design issues for field assessment of vapours
are described
- investigation and sampling techniques are
compared, and
- observations from the work are summarised.
It is found that a well-described conceptual site
model (CSM) of vapour risk embodies understanding of site conditions, potential
vapour behaviour, and priorities for investigation. It serves as the basis
for vapour risk assessment along with data quality objectives (DQOs).
Extensive vapour intrusion and assessment guidance
documentation has been developed within the United States of America and by
industry, but limited guidance is available for other countries. A
staged approach (Tier 1, 2, 3 or 4) for vapour assessment is generally adopted
across nearly all guidance, however, the breadth of investigation required in
each stage is not consistent across the available guidance. The stages of
investigation for vapour assessment do not always align with accepted stages of
a more general site investigation (Phase I or Phase II Environmental Site Assessments
– ESAs, or Preliminary/Detailed Site Investigations – PSIs/DSIs).
There is substantial information that would support
an exclusion distance approach applicable at a Tier 1 screening level,
whereby if a property or building is beyond a set distance to the edge of a
vapour source, then it could be excluded from further investigation.
Consideration of the use of soil gas vapour concentrations (representative of
the direct pathway of exposure), rather than soil concentrations alone, for
comparison to health-based investigation level (HIL) screening values seems
warranted. In Australia, this may require the development of soil gas HILs for
volatile compounds. Where soil vapour assessment techniques are not
used at Tier 1, then soil and/or groundwater investigations will be required to
assist in the definition of the exclusion distance or to provide data for
comparison to HIL screening values.
A variety of vapour assessment techniques are available.
Advantages and disadvantages of many are tabulated. Choices of vapour investigation
approaches should target improvement and modification of the CSM.
Guidance documents recommend a number of approaches. Common elements are, where
required and practical, (a) subsurface soil gas samples should be taken no
shallower than 1 m, unless adequately justified, (b) to determine maximum
vapour concentrations in the subsurface, samples should be recovered as close
as possible to the source (it is acknowledged that this may be particularly
difficult for groundwater sources and may not be warranted for very deep
sources), and (c) depth profiles can be useful. Seasonal and short term atmospheric changes
(barometric, etc.) can influence vapour concentrations but this effect
decreases rapidly with depth depending on the period of the transient
disturbance and the re-equilibration time of the vapour concentrations through
the soil profile. Vapour behaviour may need to be assessed over time where
shallow sampling is undertaken and where transient behaviour might be expected
to occur.
Most experience and investigations have been carried out for
petroleum hydrocarbons and chlorinated solvent vapours. Whilst the techniques
and approaches may be valid for use for other volatile compounds, for some
compounds (e.g. mercury, butadiene) there is limited experience, and hence
careful adoption of field approaches would be required.
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