Contaminated land dealing with hydrocarbon contamination
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Contaminated land: dealing with hydrocarbon contamination. Assessing risks to human health. Contents of presentation. CLEA and hydrocarbon-contaminated sites Alternative risk assessment approaches – what options are there? Method selection

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Contaminated land: dealing with hydrocarbon contamination

Assessing risks to human health

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

Environmental Simulations International

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

Environmental Simulations International

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 benzo[a]pyrene

      • A particular hassle for carcinogens

  • CLEA software

Environmental Simulations International

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

Environmental Simulations International

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?

Environmental Simulations International

Some questions on the exposure calculations

  • Are all of the pathways there?

    • Groundwater transport isn’t

  • 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!

Environmental Simulations International

A small selection of exposure pathways!

Environmental Simulations International

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

Environmental Simulations International

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 authority’s 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.”

Environmental Simulations International

Toxicity assessment:carcinogens

  • 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

Environmental Simulations International

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?

Environmental Simulations International


  • 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

Environmental Simulations International


  • 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 SGV’s

    • When CLEA can do the same job

    • When the conceptual model makes it inappropriate

Environmental Simulations International


  • 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 Kit:transport 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

Environmental Simulations International


  • 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

Environmental Simulations International

Or a self-coded model?

  • Infinitely flexible

    • Chose the appropriate algorithms

  • Can do probabilistic modelling

    • Own codes or commercial add-ins

      • But CLEA PDF’s proprietary

  • QA/QC must be robust

  • Needs good communication with all participating parties

Environmental Simulations International

So, which is the right method?

  • We can’t tell you – there isn’t 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

Environmental Simulations International


  • 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

Environmental Simulations International

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

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