CL:AIRE Petroleum Hydrocarbons in Groundwater: Guidance on...
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CL:AIRE Petroleum Hydrocarbons in Groundwater: Guidance on assessing petroleum hydrocarbons using existing hydrogeological risk assessment methodologies
1 © Amec Foster Wheeler 2017
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Petroleum Hydrocarbons in Groundwater
History of the guidance
What are hydrocarbons?
Why new guidance?
How does it fit in with existing guidance?
What’s in the guidance (and why)?
© Amec Foster Wheeler 20172
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History
2005 EA commission Entec to write guidance
2006 Draft guidance
2008 Revised draft
2009 Project abandoned
2016 CL:AIRE
© Amec Foster Wheeler 20173
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© Amec Foster Wheeler 20174
Products
► Petrol
► Diesel
► Kerosene
► Heating oil
► Lubricants
► Bunker fuel
► Crude oil
Compounds
► Aromatics
► BTEX compounds
► PAHS
► Aliphatics
► Alkanes
► Hexane
► Octane
► ….
What are petroleum hydrocarbons?
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Petroleum Hydrocarbons in GroundwaterThe need for additional guidance
► Commonest group of contaminants
► Need for consistent approaches to:
► Selection of analysis
► Contaminants modelled (risk drivers)
► Degradation
► NAPL
© Amec Foster Wheeler 20175
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Petroleum Hydrocarbons in GroundwaterThe Challenge
Complex mixtures► Not possible to identify every compound ► Not practical to incorporate all in a DQRA
Choice of analysis - Lots of techniques available
► Not all suitable for risk assessment► Need to avoid duplication► Need to avoid gaps
Multiple phases
► Vapour ► Free phase (mobile and residual) ► Sorbed to solid material ► Aqueous► Contaminants move between phases ► Existing methodology based on aqueous / solid phases
Identifying risk drivers can be difficult
► Hundreds of compounds present
► Variable properties / risk profile
Degradation
► Important process► Needs to be understood & quantified► No published rates for EC bands
© Amec Foster Wheeler 20176
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7
► Evaluate the risk from
hydrocarbon mixtures
► Consider analytical techniques
available
► Estimate the implications of non-
aqueous phase liquid (NAPL) for
dissolved phase groundwater
risk assessments
► Promote a lines-of-evidence
approach to evaluate the
importance of biodegradation of
other natural attenuation
processes
New Guidance – February 2017
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© Amec Foster Wheeler 2016.8
Where does it fit in?
Remedial Targets
methodology
Remedial Targets
SpreadsheetConSim Other Tools
Hydrocarbon guidance
Other guidance
Site-specific information
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© Amec Foster Wheeler 20179
1,3-Butadiene
cis-2-Butene
trans-2-Butene
2-Methyl-1-butene
2-Methyl-2-butene
cis-2-Pentene
trans-2-Pentene
Benzene
Toluene
Ethylbenzene
m-Xylene
o-Xylene
p-Xylene
1,2,4-Trimethylbenzene
1,3,5-Trimethylbenzene
1-Methyl-2-ethylbenzene
1-Methyl-3-ethylbenzene
1-Methyl-4-ethylbenzene
Isobutane
Isopentane
2,2-Dimethylbutane
2,3-Dimethylbutane
2-Methylpentane
3-Methylpentane
2,4-Dimethylpentane
2-Methylhexane
7 3-Methylhexane
2,2,4-Trimethylpentane
2,3,3-Trimethylpentane
2,3,4-Trimethylpentane
2,3-Dimethylhexane
2,4-Dimethylhexane
3-Methylheptane
Cyclopentane
Cyclohexane
Methylcyclopentane
Methylcyclohexane
n-Butane
n-Pentane
n-Hexane
n-Heptane
Naphthalene
1-Methylnaphthalene
2-Methylnaphthalene
Complex mixtures –e.g. petrol (44 compounds)
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Assessment of Complex Mixtures – Use of carbon numbers – TPHCWG
© Amec Foster Wheeler 201710
► Aromatics► EC6-EC7 (benzene)► >EC7-EC8 (toluene)► >EC8-EC10 (ethylbenzene, xylenes)► >EC10-EC12 (naphthalene)► >EC12-EC16 (anthracene)► >EC16-EC21 (pyrene)► EC21-EC35 (B[a]P)
► Aliphatic► EC5-EC6 (pentane+)► >EC6-EC8 (heptane+)► >EC8-EC10 (nonane+)► >EC10-EC12 (ondecane+)► >EC12-EC16 ► >EC16-EC21
Equivalent Carbon (EC) No. relates the boiling point of a compound to the boiling point of an equivalent n-alkane
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Analysis for Hydrocarbons
Screening analysis
► TPH / EPH / DRO / PRO
► Provide a single value or
► Limited carbon banding
► Useful in delineation / validation / remediation monitoring
Detailed analysis
► Concentration of individual compounds or discrete carbon bands. ► Targeted –named compounds
► VOCs ► SVOCs • PAHs
► Non-targeted –carbon bands with aromatic / aliphatic split► TPHCWG
Detailed analysis always required to support DQRA
© Amec Foster Wheeler 201711
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© Amec Foster Wheeler 201712
Analysis for Hydrocarbons Detailed Analysis
Name Variants Main advantages Main disadvantages
VOCs/BTEX • BTEX only
• EPA method
8260 (BTEX,
naphthalene,
trimethylbenzene
s)
• Provides quantitative
analysis of key
determinands often
quantified to low
detection levels.
• Only identifies compounds
on target list (unless TICs
are specified).
SVOCs
(speciated)
• PAHs only • Provides quantitative
analysis of key
determinands often
quantified to low
detection levels.
• Only identifies compounds
on target list (unless TICs
are specified).
Carbon
banding with
aromatic/
aliphatic
fractionation
• Different carbon
band ranges can
be specified.
• Calibration may
be against a
particular
hydrocarbon
product.
• Provides values for
carbon band ranges
rather than individual
compounds.
• Provides detail of
hydrocarbon
composition based on
the specific carbon
range defined.
• Does not detect heavy
hydrocarbons >C40
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Multiple Phases
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Multiple Phases: Considerations where NAPL present
► Spatial extent► Is NAPL is expanding, steady or declining?
► Effect on pathway length
► Vertical extent► Driving head
► Past groundwater levels
► Mobility► Risk of NAPL migration
► Residual?
► Source of dissolved phase ► Solubility of constituents
► Proportion (fraction)
► Effective solubility
► Accessibility to groundwater
► Potential for depletion of source term (declining source term)
► Potential for complex pathways► Vapour migration
► Obtaining representative samples in presence of NAPL
► Determining whether NAPL is present
► Observation
► Direct measurement
► Inferred from sampling results
© Amec Foster Wheeler 201714
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Dissolved Phase Risk from NAPL
Most models do not represent NAPLs
Standard approach
► Source is dissolved concentration in groundwater in contact with
NAPLs using Raoults Law:
C = x S
where C = effective solubility
x = mole fraction
S = free phase solubility
Example (petrol):
Mole fraction of benzene in mixture 0.0093 (0.93%)
Pure phase solubility 1780 mg/l
Effective solubility 17 mg/l
© Amec Foster Wheeler 201715
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Risk Drivers (contaminants of potential concern)
More soluble / mobile contaminants present the greatest risk► BTEX
► Naphthalene
► …
► Benzo[a]pyrene
Risk Drivers are► Soluble
► Mobile
► Persistent
► Relatively abundant
► Hazardous - compounds with EQS / DWS (toxic)
Identified by► Analysis of porewater in soils at the source area
► Analysis of groundwater close to, but downgradient of, the source area
► Product analysis and theoretical calculation (Raoult’s Law)
► Knowledge of hydrocarbon product type
© Amec Foster Wheeler 201716
Decreasing solubility / mobility
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Risk Drivers: Solubility
The relationship between Equivalent Carbon Number and Pure Phase Aqueous Solubility
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
0 5 10 15 20 25 30 35 40
Equivalent Carbon Number
Pu
re P
ha
se
Aq
ue
ou
s S
olu
bil
ity
(m
g/l
)
n-alkanes
aromatic compounds
alkynes and alkenes
cyclo-alkanes
aliphatic carbon bands
Aromatic carbon bands
Aromatics
Aliphatics
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Risk Drivers: Koc
The relationship between EC and Organic Carbon:water partition coefficient (Koc)
10
100
1000
10000
100000
1000000
10000000
100000000
1000000000
0 5 10 15 20 25 30 35 40
Equivalent Carbon Number
Ko
c (
l/k
g)
Aromatics
alkanes
alkenes/alkynes
cycloalkanes
Aliphatic carbon bands
Aromatic carbon bands
Aromatics
Aliphatics
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Risk Drivers: Mobility
10
100
1000
10000
100000
1000000
0.0001 0.001 0.01 0.1 1 10 100 1000 10000
Pure Phase Aqueous Solubility (mg/l)
Org
an
ic C
arb
on
: W
ate
r P
art
itio
n C
oe
ffic
ien
t, K
oc
(l/
kg
)
n-alkanes
Alkynes and alkenes
cyclo-alkanes
aromatics
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Recommended risk drivers
Suspected
hydrocarbon source
Carbon
banding
Recommended petroleum
hydrocarbon CoPC
Other substances of potential
concern (not crude oil derived)
Petrol (gasoline)1 C4–C12 BTEX
naphthalene
n-hexane
Ether oxygenates (MTBE,
TAME, ETBE, DIPE) 3
Lead scavengers 4
Kerosene (jet fuel)1 C6–C16 BTEX
TPHCWG5
2-methylnaphthalene1
Light lubricating oils C6–C10 TPHCWG5
Diesel/ domestic
heating oil1,2
C8–C21 BTEX
TPHCWG5
2-methylnaphthalene1
Heavy fuel oils C12+ TPHCWG5
Lubricating oils and
greases
C18->C34 TPHCWG5
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Biodegradation
Hydrocarbons degrade
► Carbon dioxide and water
Rates vary
► Fast (days) to slow (years)
► Depend on
► Compound
► Simple vs complex
► Structure (e.g. aromatic vs aliphatic)
► Hydrochemistry e.g.
► Electron acceptors
► Competition
► Aquifer type
Variable information availability
► BTEX - lots
► PAHs - limited
► TPH-CWG – none
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Degradation – Assessing the Evidence
Lines-of-evidence (MNA guidance)
► Primary: loss of contaminant mass or decrease in concentration
► Secondary: geochemical and biochemical indicators
► Tertiary: microbiological data
Evaluation of geochemical environment.
► Aerobic or anaerobic?
Electron balance
► Are there sufficient oxidants (oxygen, nitrate, sulphate, iron and
manganese) to degrade the mass of hydrocarbon in the aquifer?
Using analytical or numerical models
► Calculate the extent of the plume for comparison with field results
Ignoring degradation
► Conservative assessment
© Amec Foster Wheeler 201722
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Conclusion
New Guidance Issued in February 2017
► Sets out existing good practice
► Supplementary to existing risk assessment methodologies
► Remedial Targets Methodology
► Sets out approaches to:
► Analysis
► NAPL
► Risk Drivers
► Degradation
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Acknowledgements
Amec Foster Wheeler
► Mike Carey
Environment Agency
► Kirsten Johnstone
CL:AIRE
► David Brown, Shell Global Solutions International B.V.
► Nicola Harries, CL:AIRE
► Jonathan Smith, Shell Global Solutions (UK) Ltd
► Rob Sweeney, CL:AIRE
► Lucy Thomas, RSK Group
© Amec Foster Wheeler 201724