Contaminated land: dealing with hydrocarbon contamination

1
Contaminated land dealing with hydrocarbon
contamination

• Assessing risks to human health

2
Contents of presentation

• CLEA and hydrocarbon-contaminated sites
• Alternative risk assessment approaches what
  options are there?
• Method selection
• Dutch screening values, SNIFFER, RBCA, RISC
  Workbench, Risc-Human
• Evaluation

3
CLEA a reminder

• Application determination of Soil Guideline
  Values for human health in relation to long-term
  (chronic) exposures to contaminated soil
• For the specified conceptual models
• Using the specified algorithms

Previous CIEH training
4
CLEA available tools

• Main reports (CLR 7, 8, 9 and 10)
• Daughter reports for individual substances
• Presently, those of main relevance to
  hydrocarbon-contaminated sites are the documents
  for lead and benzoapyrene
• A particular hassle for carcinogens
• CLEA software

5
CLEA does not

• Function directly as a site-specific risk
  assessment tool
• But the algorithms, exposure parameters and
  toxicity data can be so used
• Assess human health risks by all potential
  pathways
• Deal with acute exposures (except cyanide)
• Help in CDM and related assessments
• Assess risks to other receptors
• Replace expert judgement

6
A note on contaminant sources in CLEA

• At surface for soil ingestion, dermal contact,
  inhalation of dust
• Directly beneath base of building
• Directly under house (for indoor inhalation of
  vapour)
• At 1 m depth for outside inhalation of vapour
• Assumed to be in equilibrium

Do these match with the conceptual model for your
hydrocarbon-contaminated site?
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Some questions on the exposure calculations

• Are all of the pathways there?
• Groundwater transport isnt
• Are the vapour transport algorithms appropriate
  for the conceptual model
• Does the dermal uptake algorithm give a suitable
  assessment for hydrocarbons
• Is the plant uptake algorithm suitable?
• e.g., US EPA PAH adjustment

They may be no problem but we must ask the
questions!
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A small selection of exposure pathways!
9
Groundwater transport and human health?

• In the UK, for risks associated with
  ground/surface water ingestion, we cannot use a
  risk-based approach to determine drinking water
  concentrations
• Maximum contaminant concentrations are set out in
  the Water Regulations (2000)
• Assessment may also be required when hydrocarbons
  enter the water source directly or by permeation
  through pipework

10
Alternative risk assessment options?

• the local authority should be prepared to
  reconsider any determination based on such use of
  guideline values if it is demonstrated to the
  authoritys satisfaction that under some more
  appropriate method of assessing the risks the
  local authority would not have determined that
  the land appeared to be contaminated land.

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Toxicity assessmentcarcinogens

• UK Netherlands uses the Index Dose
• The dose which can be considered to present a
  minimal human health risk from exposure to soil
  contaminants
• Although NL exposure factors are very different
• US uses the slope factor method
• Determines the dose at which there is an
  acceptable risk of incidence (usually 1 in 105 or
  106)
• Not accepted by the DoH

12
A note on the Dutch screening values

• Easily and widely used
• And plenty of hydrocarbon components
• But
• Certain pathways only
• Based on different exposure periods and
  assumptions to UK approaches
• Have they been adjusted for the right soil type?

13
SNIFFER

• SNIFFER report LQ01
• Guide to good practice for the development of
  conceptual models and the selection and
  application of mathematical models of contaminant
  transport processes in the subsurface SNIFFER,
  2003
• Algorithms similar to CLEA but uses some
  alternatives that may be of interest for
  hydrocarbon sites
• Examples vapour transport, plant uptake
• Standard land uses directly
• Other land uses by application of parameters and
  algorithms

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SNIFFER

• Can be used to derive site-specific assessment
  criteria
• Site-specific risk assessment tool
  (worksheet-based)
• Standard land uses directly
• Other land uses by application of parameters and
  algorithms
• Do not use
• When there is a relevant SGV
• To derive SGVs
• When CLEA can do the same job
• When the conceptual model makes it inappropriate

15
RBCA

• ASTM RBCA standard (E2081-00)
• Very widely used
• Well-documented
• US parameters
• But slope factors are used to determine
  carcinogenic risk
• Deterministic
• Includes soil vapour transport model
• Includes groundwater transport

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RBCA Tool Kittransport models
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RISC Workbench (BP RISC)

• Compatible with/extends RBCA methodology
• Slope factors are used to determine carcinogenic
  risk
• Good range of defaults for contaminants, aquifers
  soil types
• Probabilistic assessment for many variables
• Models can be used with stationary free-phase
  contaminants
• Includes a soil vapour transport model
• Includes groundwater transport

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Risc-Human

• Index Dose is used to calculate risks from
  genotoxic carcinogens
• Comprehensive list of pathways targets
• Includes a soil vapour transport model
• Can use subsites and scenarios to store different
  model runs
• Large range of organic compounds
• Probabilistic assessment for many variables

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Or a self-coded model?

• Infinitely flexible
• Chose the appropriate algorithms
• Can do probabilistic modelling
• Own codes or commercial add-ins
• But CLEA PDFs proprietary
• QA/QC must be robust
• Needs good communication with all participating
  parties

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So, which is the right method?

• We cant tell you there isnt a right answer
• The appropriate risk assessment methodology
  depends on the conceptual model
• Hydrocarbons and other contaminants of concern
• Pathways
• Suitable algorithms
• Beware inappropriate parameterisation
• Beware inappropriate TDSI and Index Doses
• Especially the latter from non-UK sources

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Conclusions

• The best tool for any risk assessment job is that
  with the appropriate conceptual model and
  sufficient flexibility to enable use of
  site-specific parameters
• A wide range of methodologies exist to quantify
  risks to human health
• Each has its own approach for the source,
  exposure routes, transport processes and
  receptors
• Different simplifications
• Different processes
• Sometimes these differences are subtle, but can
  lead to significantly different results

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Risk assessment methods - some things to question

• Does the user understand the underlying
  assumptions and conceptual models in the
  methodology?
• Calculation of risk from non-threshold substances
• The right pathways
• Reasonable UK exposure parameters
• Critical receptors
• Appropriate algorithms (and why chosen)
• Probabilistic modelling