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

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Presentation on theme: "Contaminated land: dealing with hydrocarbon contamination Petroleum hydrocarbons – occurrence, composition and significance."— Presentation transcript:

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

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

3 Environmental Simulations International Potential hydrocarbon- contaminated sites – 1 n 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

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

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

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

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

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

9 Environmental Simulations International Aromatic hydrocarbons - BTEX Benzeneo-Xylene C 6 H 6 C 8 H 11 Toluenem-Xylene C 7 H 8 C 8 H 11 Ethylbenzenep-Xylene C 8 H 10 C 8 H 11 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 3 CH 2 CH 3

10 Environmental Simulations International Aromatic hydrocarbons – PAH’s Polycyclic aromatic hydrocarbons (PAH) [polynuclear aromatic hydrocarbons (PNA)] NaphthaleneBenzo(a)Pyrene C 10 H 8 C 20 H 12 PhenanthreneDibenzo(a,h)Anthracene C 14 H 10 C 22 H 14 PyreneFluoranthene C 16 H 10

11 Environmental Simulations International Relative distribution of components – an example

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

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

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

15 Environmental Simulations International Why is NAPL important? n Direct effects of oil at receptor –Also potential effect on buried materials n 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

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

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

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

19 Environmental Simulations International MTBE Methyl tertiary butyl ether CH 3 C CH 3 O CH 3 Additives in unleaded petrol TAME Tertiary methyl amyl ether C2H5C2H5 C CH 3 O CH 3 ETBE Ethyl tertiary butyl ether CH 3 C CH 2 CH 3 O CH 3 MTBE most common in UK Typically 1-5% in petrol Highly soluble (26000 mg/l) Very low taste/odour threshold

20 Environmental Simulations International Weathering n 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 n Weathering of organic lead additives

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

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

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


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