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Contaminated land: dealing with hydrocarbon contamination

Contaminated land: dealing with hydrocarbon contamination. Assessing risks to other receptors. Contents of presentation. Risk assessment for controlled waters Risk assessment for ecological receptors Risk assessments of hydrocarbon impact on buildings and services.

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Contaminated land: dealing with hydrocarbon contamination

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  1. Contaminated land: dealing with hydrocarbon contamination Assessing risks to other receptors

  2. Contents of presentation • Risk assessment for controlled waters • Risk assessment for ecological receptors • Risk assessments of hydrocarbon impact on buildings and services Environmental Simulations International

  3. Risk assessment for controlled waters • Environment Agency Remedial Targets Methodology (R&D 20) • A tiered (4) methodology for assessment of risk to aquifers and surface water bodies • Deterministic and probabilistic at different tiers • Applied in Part IIA assessments, planning, etc. when such receptors are identified by the conceptual model as being at risk • Requires a robust conceptual model Environmental Simulations International

  4. The tiers • “in moving through from Tier 1 to Tier 4 the data requirements and resources required increase, but the degree of conservatism in the approach decreases and the cost-effectiveness of the final remedial solution is likely to improve” Data requirements Conservatism Environmental Simulations International

  5. Compliance Point Source Areas Soil Source Target Concentration GW Source Key definitions • Compliance Point: Point along pathway where target concentration should not be exceeded • Target Concentration (CT): The concentration at the compliance point that should not be exceeded (normally water quality standard or background) Environmental Simulations International

  6. Key definitions • Remedial Target: Source concentration above which remediation is required • LTC - Liquid Remedial Target (porewater in soil source) • STC - Soil Remedial Target (soil source) Remedial Target Concentration Compliance Point Target Concentration Soil Source GW Source Environmental Simulations International

  7. Setting target concentrations • Consider: • Requirements of EU and UK Law (e.g. Groundwater Directive) • Background water quality of water resources • Whether receptor is a resource • Targets should be set to provide greatest appropriate level of protection • EQS, DWS, others? Environmental Simulations International

  8. Assessment of soil sources • Effect of soil contamination on: • Previously uncontaminated groundwater • Downgradient receptor via groundwater pathway Environmental Simulations International

  9. Assessment of soil sources • Tier 1 • Are soil pore water concentrations acceptable? • Tier 2 • Will the site-specific dilution factor (DF; usually in groundwater immediately below the source) result in acceptable concentrations? • Tier 3 • Applies attenuation factor (AF) between source and receptor (downgradient groundwater or surface water receptor) Environmental Simulations International

  10. Assessment of soil sources • Tier 4 • Develops Tier 3 using a more detailed and accurate (custom) simulation of subsurface processes and geometry to determine concentrations at the receptor Environmental Simulations International

  11. Assessment of groundwater sources • Effect of groundwater contamination on: • Previously uncontaminated groundwater • Downgradient receptor via groundwater pathway Environmental Simulations International

  12. Assessment of groundwater sources • Tier 2 • Is observed groundwater already acceptable? • Tier 3 • Applies attenuation factor (AF) between source and receptor (downgradient groundwater or surface water receptor) • Tier 4 • Develops Tier 3 using a more detailed and accurate (custom) simulation of subsurface processes and geometry to determine concentrations at the receptor Environmental Simulations International

  13. Particular hydrocarbon assessment issues • NAPL phase determination - And will it migrate? • Numerous components • Key representative compounds • Interactions • History of source and migration • Weathering • Past and future • Short circuiting • Also by vapour Environmental Simulations International

  14. Some software tools • Remedial Targets Methodology • Tiers 1-3 only • ConSim / LandSim • RAM • RBCA Tool Kit • RISC Workbench • Groundwater modelling packages See benchmarking study in: Whittaker et al., 2001 Environmental Simulations International

  15. Why ecological risk assessment? • Prevention of significant harm to designated locations • Part IIA, EPA 1990 • IPPC regime • Waste Management Regs. • COMAH – limit consequences of major hazards on the environment Environmental Simulations International

  16. What is significant harm? • Substantial, irreversible impact on ecological system function and endangerment of long-term maintenance of a population Part IIA • [Impacting] the coherence of its ecological structure & function, across its whole area, that enables it to sustain the habitat, complex of habitats and/or the levels of populations of the species for which it was classified PPG9 Environmental Simulations International

  17. Sites of Special Scientific Interest (SSSIs) National Nature Reserve (NNR) Marine Nature Reserve (MNR) Other Nature Reserves (candidate) Special Areas for Conservation (cSAC) Special Protection Areas (SPAs) Areas of Special Protection for Birds A selection of designated locations Environmental Simulations International

  18. Potential receptors • Soil fertility • Ability of soil to support plant growth and soil fauna critical to maintenance of food webs • Surface waters and associated sediments • Rivers, streams, ponds, lakes…… • Terrestrial habitats • Marshland, meadows…… • Specific protected species Environmental Simulations International

  19. Principles and challenges • The concept of “harm” • How to define and quantify harm? • Which test methods are appropriate? • How to define significance? • How do you deal with natural perturbations? • How do you handle the effects of mixtures • Based on source-pathway-receptor linkage • Need conceptual site model • Identify plausible exposure scenarios • Tiered approach/cost-benefit evaluation Environmental Simulations International

  20. Ecological risk assessment guidance • Developing but at present • Environment Agency guidance • Tier 1. Screening • Tier 2. Testing and detailed evaluation • Tier 3. Detailed testing and evalation • SNIFFER • Worksheets for numerical targets (NTF, NTS) • Broadly similar to Tier 1 Environmental Simulations International

  21. Risk assessment to structures • Buildings, foundations, underground services • See Environment Agency R&D report P5-035/TR/01 • Particular issues with hydrocarbons • Diffusion into water pipes • Entry into sewers • Attack on plastics • Softening of asphalt Environmental Simulations International

  22. Conclusions • The risk assessment frameworks have common basis • Source-pathway-receptor • Tiered assessment • All risk assessment frameworks have equal applicability in Part IIA assessments and planning process • It’s more than just CLEA • Hydrocarbon is no different in principle to other contamination • But some specific properties need to be considered Environmental Simulations International

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