Contaminated land: dealing with
hydrocarbon contamination
Remediation options for
petroleum hydrocarboncontaminated soil and
groundwater
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

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Remedial objectives

Risk management (derived from risk
assessment)
– Remove the source
– Break the pathway
– Remove the receptor



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Not usually an option!
Which contaminants?
Appropriate cost-benefit performance
Are there specific local requirements?
Previous CIEH training on remediation technologies
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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
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Main remedial options for
petroleum hydrocarbons
Approach
Applied at
Source
Pathway
Move receptor

Restrict access

Excavate & treat

Pump & treat

Barriers/PRB’s


SVE & related

In situ bioremediation
Thermal techniques
Receptor
()


MNA

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Ex situ remediation

Soil
– Excavate
– Excavate
– Excavate
– Excavate

and
and
and
and
landfill
biotreat
thermal treatment
soil wash
Groundwater
– Pump & treat
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Adequate
definition of
area to be
removed?
Excavate & landfill

“Dig and dump”
– Historically the “default
option” for soils
– Future constraints



Legislative
Cost
Total environmental impact
– emissions, truck movements, etc.
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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?
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How biodegradable are
petroleum hydrocarbons?
“Rapid”
“Moderate”
“Slow”
BTEX
Highly substituted
monoaromatics
Asphaltenes
Naphthalenes
n-alkanes <C20
n-alkanes C20 –
C40
Branched alkanes
3-4 ring PAH’s
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alkanes >C40
cycloalkanes
>4 ring PAH’s
Ex situ biotreatment
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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
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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
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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
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In situ remediation
Barrier and PRB technologies
 SVE and related technologies
 Bioremediation

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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
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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
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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…
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SVE and variants
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SVE and variants


Well-established
Some common questions
–
–
–
–
Subsurface permeability
Subsurface heterogeneity
Effectiveness for MTBE
Emissions treatment


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Thermal oxidisers
Activated carbon
Biofilters
– Groundwater management
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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
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“In situ bioreactor”
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Biological PRB using ORC
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In situ flushing


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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
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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
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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
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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
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Hydrocarbon MNA site
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UK MNA case summary

Primary line of evidence: mass removal
by biodegradation
– Plume: front stationary and area reducing
– Benzene concentrations decreasing

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Rates vary within plume
Inversely proportional to concentration?
Seasonal effects
Rate at plume front = 0.2%/day
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NA data for benzene
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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
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Technologies for NAPL
remediation?

Limited “source” excavation
– Access permitting!

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NAPL pumping
SVE/HVE/bioventing
 Depending
Sparging/biosparging/slurping  on
Ex situ bioremediation
 components
…… or deal with the pathway(s)
– Pump & treat, trench, etc.
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Pumping NAPL

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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
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Technologies for MTBE
remediation
Unsaturated soil
 Excavation and
disposal
 SVE and variants
Groundwater
 Pump & treat
– Difficult to treat water

– Limited efficiency due
to partitioning
behaviour

Bioremediation
– Not straightforward
Sparging & variants
– Limited efficiency due
to partitioning
behaviour

Bioremediation
– Not straightforward
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Monitoring & verification
Objectives may include:
1. Confirmation of risk
assessment findings
2. Confirmation of
remediation performance
3. Determination of when
remediation can cease
4. Indication of the need for
corrective action
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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…
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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
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Monitoring NAPL thickness
1.6
Why is the thickness changing?
1.4
• Groundwater fluctuations (smearing)?
• Product trapping?
• Weathering?
• Remediation?
• A combination of the above?
FPH thickness (m)
1.2
1
0.8
0.6
0.4
0.2
0
Oct-95
May-96
Dec-96
Jun-97
Jan-98
Jul-98
Feb-99
Date
Figure 4. Changes in FPH thickness in MW 42 at the NIA site
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Aug-99
Mar-00
Conclusions

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There are diverse remediation options for
petroleum hydrocarbons
Important drivers
–
–
–
–

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Risk management
Fitness-for-purpose
Cost-benefit
Duration
Ask the right questions! (And beware the
sales pitch).
Appropriate verification/monitoring
– Duration?
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Conclusions
A combination of techniques is often the appropriate option
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