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Contaminated land: dealing with hydrocarbon contamination

Contaminated land: dealing with hydrocarbon contamination. Petroleum hydrocarbons – occurrence, composition and significance. Contents of presentation. Sources of hydrocarbon contamination Composition of oils Non-hydrocarbon components of oil Hydrocarbon behaviour in the subsurface

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Contaminated land: dealing with hydrocarbon contamination

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  1. Contaminated land: dealing with hydrocarbon contamination Petroleum hydrocarbons – occurrence, composition and significance

  2. Contents of presentation • Sources of hydrocarbon contamination • Composition of oils • Non-hydrocarbon components of oil • Hydrocarbon behaviour in the subsurface • The most important components? Environmental Simulations International

  3. Potential hydrocarbon-contaminated sites – 1 • Stating the obvious • Filling stations, distribution depots • Oil production, refineries and associated • Garages/automotive industry • Haulage yards • Scrap metal industry • Airports, aerospace industry • Waste processing & disposal Environmental Simulations International

  4. Potential hydrocarbon-contaminated sites – 2 • And also… • Gasworks • Metalworking industry • Paints/inks/coatings industry • Anybody who uses solvents! • Agricultural facilities • Anywhere with a boilerhouse/ furnace • Including domestic oil storage Environmental Simulations International

  5. Composition of oils • Crude oil and petroleum products are complex mixtures • They are characterised by differing boiling point ranges and components • Carbon numbers/simulated distillation Environmental Simulations International

  6. Oil refining Gasoline C4-C10 (80oC - 150oC) Kerosene/Jet Fuel C11-C13 (150oC - 250oC) Diesel Fuel C14-C18 (250oC - 325oC) Crude Oil Heavy Gas Oil C19-C25 (325oC - 450oC) Lubricating Oil C26-C40 (450oC - 500oC) Residuum >C40 (> 500oC) Environmental Simulations International

  7. Main component groups • Aliphatic hydrocarbons • Aromatic hydrocarbons • NSO components • Nitrogen, sulphur and oxygen-containing compounds • “Polar components” • “Asphaltenes” Environmental Simulations International

  8. C C C C C C C C C C C C Aliphatic hydrocarbons • Alkanes Saturated hydrocarbons - no double or triple bonds. • (Paraffins) • Hexane • Alkenes/ Unsaturated hydrocarbons - double/triple bonds. • Alkynes • (Olefins) • Hexene • Cycloalkanes Saturated hydrocarbons with a ring structure. • (Naphthenes) • Cyclohexane Environmental Simulations International

  9. C H 3 C H 3 C H C H 3 3 C H C H 3 C H C H 2 3 C H 3 Aromatic hydrocarbons - BTEX Benzene o-Xylene C6H6 C8H11 Toluene m-Xylene C7H8 C8H11 Ethylbenzene p-Xylene C8H10 C8H11 3 Environmental Simulations International

  10. Polycyclic aromatic hydrocarbons (PAH) [polynuclear aromatic hydrocarbons (PNA)] Naphthalene Benzo(a)Pyrene C10H8 C20H12 Phenanthrene Dibenzo(a,h)Anthracene C14H10 C22H14 Pyrene Fluoranthene C16H10 C16H10 Aromatic hydrocarbons – PAH’s Environmental Simulations International

  11. Relative distribution of components – an example Environmental Simulations International

  12. Hydrocarbon behaviour in the subsurface • Oil is a light non-aqueous phase liquid (LNAPL) • Residual oil will be held in pore spaces in soil • Free oil “floats” on groundwater • The more soluble components can dissolve in groundwater • MTBE & TAME are highly soluble • The more volatile components can partition into soil gas • Sorption of components into/onto soil can be an important process Environmental Simulations International

  13. Residual Hydrocarbons in Soil Pores (soil contamination) (~1% HC by weight) Volatilised Constituents (vapour plume) (~50mg HC/kg soil) Mobile & Residual Hydrocarbons (free-product) (~9% by weight) After Oil Flow Through Soil Dissolved Constituents (plume) (~130 mg HC/L water) How oil components might be distributed Petrol Spill soil surface Before Oil Flow Through Soil vadose zone During Oil Flow Through Soil capillary fringe water table saturated zone groundwater flow Environmental Simulations International

  14. NAPL – how? Oil in closed-end pore Residual oil trapped by water Soil Matrix Soil Matrix NAPL NAPL Trapped NAPL Wetting Fluid (water) Environmental Simulations International

  15. Why is NAPL important? • Direct effects of oil at receptor • Also potential effect on buried materials • Residual NAPL can also be a source of contamination for long periods of time • Water soluble components can cause long-term groundwater plumes • Volatile components are a potential source of vapours Environmental Simulations International

  16. Petroleum contamination – what to look for • Liquid phase (free-product NAPL) • Dissolved phase (groundwater plume) • Solid phase (hydrocarbon attached to soil) • Vapour phase • Combination of several phases Environmental Simulations International

  17. BENZENE TOLUENE m-XYLENE p-XYLENE Vapour ETHYLBENZENE Water o-XYLENE Sorbed NAPHYTHALENE 2-METHYLNAPHTHALENE ACENAPHTHYLENE ACENAPHTHENE 0% 20% 40% 60% 80% 100% How oil components might be distributed – example Environmental Simulations International

  18. Non-hydrocarbon components • Organic additives • Petrol (gasoline): MTBE, TAME • Fuels: proprietary performance additives • Luboils: proprietary performance additives • Metals • Naturally occurring components of crude • e.g., vanadium, nickel • Significant contaminants in waste luboils • Leaded petrol (TEL) • Max. 0.013 g/l in 1980’s leaded petrol but earlier or special use petrol could be higher • Proprietary performance additives Environmental Simulations International

  19. CH3 C2H5 CH3O C CH3 CH3O C CH3 CH3 CH3 CH3 CH2CH3O C CH3 CH3 Additives in unleaded petrol MTBE Methyl tertiary butyl ether TAME Tertiary methyl amyl ether ETBE Ethyl tertiary butyl ether • MTBE most common in UK • Typically 1-5% in petrol • Highly soluble (26000 mg/l) • Very low taste/odour threshold Environmental Simulations International

  20. Weathering • Preferential reduction in the concentration of some components relative to others • Biodegradation tends to favour removal of n-alkanes (straight carbon chain alkanes), low molecular weight cycloalkanes and light aromatics • Volatilisation and dissolution tends to remove low molecular weight aromatics (especially BTEX) and aliphatics • Dissolution is very important for MTBE and TAME • Weathering of organic lead additives Environmental Simulations International

  21. 30 C20 20 C25 Wt % C15 C30 10 0 n- iso- cyclo- 30 20 Wt % 10 0 n- iso- cyclo- 30 20 Wt % 10 0 6-rings 2 4 Weathering – aliphatic components • So, weathered hydrocarbon mixtures are typically significantly less mobile and less toxic than “fresh” mixtures Environmental Simulations International

  22. Summary • Hydrocarbon contamination may arise at a wide variety of sites • Crude oils and petroleum products are complex mixtures of components • We will discuss the implications further in more detail • Multiphase behaviour must be considered • Weathering may be important Environmental Simulations International

  23. The most important components? • Certain groups of components often merit particular (but not sole) consideration, e.g. • BTEX • Toxicity, vapours • PAH’s • Potential carcinogenicity, relatively persistent • BUT this depends on the source-pathway-receptor relationships that you are considering • Is the conceptual model sound? Environmental Simulations International

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