Contaminated land: dealing with hydrocarbon contamination

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?

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

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

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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

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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 gtC40 (gt 500oC)
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Main component groups

• Aliphatic hydrocarbons
• Aromatic hydrocarbons
• NSO components
• Nitrogen, sulphur and oxygen-containing compounds
• Polar components
• Asphaltenes

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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
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Aromatic hydrocarbons - BTEX
Benzene o-Xylene C6H6
C8H11 Toluene m-Xylene C7H8
C8H11 Ethylbenzene p-Xylene C8H10
C8H11
3
10
Aromatic hydrocarbons PAHs
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Relative distribution of components an example
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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

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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
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NAPL how?
Oil in closed-end pore
Residual oil trapped by water
Soil Matrix
Soil Matrix
NAPL
NAPL
Trapped NAPL
Wetting Fluid (water)
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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

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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

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How oil components might be distributed example
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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 1980s leaded petrol but
  earlier or special use petrol could be higher
• Proprietary performance additives

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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

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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

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Weathering aliphatic components

• So, weathered hydrocarbon mixtures are typically
  significantly less mobile and less toxic than
  fresh mixtures

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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

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The most important components?

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