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Contaminated land: dealing with hydrocarbon contamination

Contaminated land: dealing with hydrocarbon contamination. Remediation options for petroleum hydrocarbon-contaminated soil and groundwater. Contents of presentation. Remedial objectives Ex situ remediation techniques In situ remediation techniques Monitored natural attenuation

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Contaminated land: dealing with hydrocarbon contamination

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  1. Contaminated land: dealing with hydrocarbon contamination Remediation options for petroleum hydrocarbon-contaminated soil and groundwater

  2. Contents of presentation • Remedial objectives • Ex situ remediation techniques • In situ remediation techniques • Monitored natural attenuation • Some comments on NAPL remediation • Some comments on MTBE • Monitoring and verification Environmental Simulations International

  3. Remedial objectives • Risk management (derived from risk assessment) • Remove the source • Break the pathway • Remove the receptor • Not usually an option! • Which contaminants? • Appropriate cost-benefit performance • Are there specific local requirements? Previous CIEH training on remediation technologies Environmental Simulations International

  4. Remediation selection and licensing • Beyond the scope of this presentation! • But feel free to cover in discussion • Licensing might include • Planning requirements • Mobile plant licence • Waste management licence • IPPC Environmental Simulations International

  5. Main remedial options for petroleum hydrocarbons Environmental Simulations International

  6. Ex situ remediation • Soil • Excavate and landfill • Excavate and biotreat • Excavate and thermal treatment • Excavate and soil wash • Groundwater • Pump & treat Adequate definition of area to be removed? Environmental Simulations International

  7. Excavate & landfill • “Dig and dump” • Historically the “default option” for soils • Future constraints • Legislative • Cost • Total environmental impact • emissions, truck movements, etc. Environmental Simulations International

  8. Excavate & biotreat • Hydrocarbon degradation in oxygenated treatment systems • Windrows, biopiles, etc. • Well-established • Some common questions • Contaminant availability/residuals • Speed of treatment • Volatilisation • Leachate control • Indigenous or added microorganisms? Environmental Simulations International

  9. How biodegradable are petroleum hydrocarbons? “Rapid” BTEX Naphthalenes n-alkanes <C20 “Moderate” Highly substituted monoaromatics n-alkanes C20 – C40 Branched alkanes 3-4 ring PAH’s “Slow” Asphaltenes alkanes >C40 cycloalkanes >4 ring PAH’s Environmental Simulations International

  10. Ex situ biotreatment Environmental Simulations International

  11. Excavate & thermal treatment • Hydrocarbons, etc. desorbed from soil at elevated temperatures • e.g., rotary kiln • Off-gas treatment • e.g., catalytic or thermal oxidiser • Straightforward technology but rarely used • Some common questions • Emissions control • Fuel use • Economics • Properties of treated soil Environmental Simulations International

  12. Excavate & soil wash • Hydrocarbon removal from soil by water/agitation; treatment of process streams • Often pushed as method for PAH remediation • Some common questions • Process engineering (blockage, attrition, etc.) • Slurry handling • Water treatment • Economics Environmental Simulations International

  13. Pump and treat • Break pathway by abstraction of groundwater; treat groundwater • Really a containment technology • Some common questions • How long to pump for? • Pump water and/or NAPL? • Water treatment technology • Hydrocarbons and other components • Treated water discharge • Long-term costs Environmental Simulations International

  14. In situ remediation • Barrier and PRB technologies • SVE and related technologies • Bioremediation Environmental Simulations International

  15. Barrier techniques • Variants • Capping • Cut-off walls (barriers) • Solidification • Well-proven • But solidification a questionable option for hydrocarbons • Some common questions • Long-term performance • Ensuring integrity Environmental Simulations International

  16. Permeable reactive barriers (PRB’s) • Reactive zones installed across the groundwater plume to enhance contaminant removal or degradation • For hydrocarbons, this is mostly likely to involve enhancements of in situ bioremediation • We will consider this in a few slides time Environmental Simulations International

  17. SVE and variants • Removal of volatile components by moving air through • Soil (SVE; high vacuum extraction (HVE)) • Groundwater (In situ air sparging (IAS)) • Can be combined with removal of contaminated groundwater and/or NAPL • Slurping (multiphase extraction) • Can be combined with enhanced biodegradation • Bioventing, bioslurping… Environmental Simulations International

  18. SVE and variants Environmental Simulations International

  19. SVE and variants • Well-established • Some common questions • Subsurface permeability • Subsurface heterogeneity • Effectiveness for MTBE • Emissions treatment • Thermal oxidisers • Activated carbon • Biofilters • Groundwater management Environmental Simulations International

  20. In situ bioremediation • Contaminant degradation by stimulating biological activity in the subsurface • Note: hydrocarbon degradation is most effective in the presence of oxygen • Many variants on basic process configuration • Some common questions • Can you supply enough oxygen? • Inhibitory effects? • Distribution of additives • Biofouling problems • Speed Environmental Simulations International

  21. “In situ bioreactor” Environmental Simulations International

  22. Biological PRB using ORC Environmental Simulations International

  23. In situ flushing • Addition of solvent or surfactant to subsurface to enhance solubility of NAPL for recovery by pumping • Much talked about, little used for remediation • Some common questions • Getting the additives to the right place • Getting the additives back • Effects of additives on soil structure • Economics Environmental Simulations International

  24. Monitored natural attenuation (MNA) • Natural attenuation • The effect of combined naturally occurring physical, chemical and biological processes to reduce the risk posed by polluting substances in groundwater to the identified receptors. • Monitored natural attenuation • Monitoring of groundwater to confirm that NA processes are acting at a sufficient rate to protect receptors and that remedial objectives will be achieved within a reasonable timescale Environmental Simulations International

  25. MNA • Widely used in US and elsewhere • UK guidance (R&D P95) • Some common questions • Duration appropriate? • Long-term cost-benefit? • Monitoring requirements • Ensuring continuity • Contingency requirements Environmental Simulations International

  26. UK MNA case summary • UK oil distribution terminal • Gasoline additive release early-1970’s • NA monitored since April 1994 • Risk-based approach • Sandy aquifer • Potential minor aquifer • Dissolved plume 9-14 m b.g.s. • Velocity 15-50 m/year Environmental Simulations International

  27. Hydrocarbon MNA site Environmental Simulations International

  28. UK MNA case summary • Primary line of evidence: mass removal by biodegradation • Plume: front stationary and area reducing • Benzene concentrations decreasing • Rates vary within plume • Inversely proportional to concentration? • Seasonal effects • Rate at plume front = 0.2%/day Environmental Simulations International

  29. NA data for benzene Environmental Simulations International

  30. UK MNA case summary • Secondary evidence: geochemical • O2, NO3- and SO42- depletion with increasing BTEX • Stoichiometrically, available SO42- could account for 43 mg benzene/litre: sufficient • Tertiary evidence: microbiological • High microbial numbers, including large sulphate-reducing population Environmental Simulations International

  31. Technologies for NAPL remediation? • Limited “source” excavation • Access permitting! • NAPL pumping • SVE/HVE/bioventing • Sparging/biosparging/slurping • Ex situ bioremediation • …… or deal with the pathway(s) • Pump & treat, trench, etc. • Depending • on • components Environmental Simulations International

  32. Pumping NAPL • Works best for light products/recent releases, significant thicknesses and coarse formations • NAPL becomes trapped below the water table if pumping stops • NAPL will not flow after it reaches residual saturation • Many case studies have shown that most of the NAPL remains in place due to trapping • Oil/water separation is difficult if product becomes emulsified during pumping Environmental Simulations International

  33. Unsaturated soil Excavation and disposal SVE and variants Limited efficiency due to partitioning behaviour Bioremediation Not straightforward Groundwater Pump & treat Difficult to treat water Sparging & variants Limited efficiency due to partitioning behaviour Bioremediation Not straightforward Technologies for MTBE remediation Environmental Simulations International

  34. Monitoring & verification Objectives may include: • Confirmation of risk assessment findings • Confirmation of remediation performance • Determination of when remediation can cease • Indication of the need for corrective action Environmental Simulations International

  35. Soil sampling • Basic guidance in CLR7 • Mean and maximum value tests to determine compliance with target concentrations • Useful for relatively straightforward sites but does not consider spatial distribution of contamination • Geostatistics • Specialist advice… Environmental Simulations International

  36. Groundwater monitoring • Where? • Appropriate to site layout and remediation process • Upgradient/downgradient • Compliance points/sentinel wells • What? • Contaminants posing significant risk • Process indicators/geochemical parameters? • When? • Depends on the site and the process • Establish performance baseline • Establish seasonality • Can always reduce frequency once the situation is understood Environmental Simulations International

  37. Monitoring NAPL thickness • Why is the thickness changing? • Groundwater fluctuations (smearing)? • Product trapping? • Weathering? • Remediation? • A combination of the above? Environmental Simulations International

  38. Conclusions • There are diverse remediation options for petroleum hydrocarbons • Important drivers • Risk management • Fitness-for-purpose • Cost-benefit • Duration • Ask the right questions! (And beware the sales pitch). • Appropriate verification/monitoring • Duration? Environmental Simulations International

  39. Conclusions A combination of techniques is often the appropriate option Environmental Simulations International

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