1
Contrasts in LNAPL Risk Factors for
Different Petroleum Products
Presented by:
G.D. Beckett, PG, CHG; AQUI-VER, INC.
Douglas Bell, PG; Dillon Consulting
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Simulated Transient LNAPL Release, 2 Darcy Sand Time 0
S
N
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Simulated Transient LNAPL Release, Time 1 Early-Time
S
N
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Simulated Transient LNAPL Release, Time 2 Mid-Time
S
N
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Simulated Transient LNAPL Release, Time 3 Late-Time
S
N
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2
Two Key Components - Both Important
Physics of Release
Chemistry of Release
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The Range of Impacts Depend on the LNAPL
1. Distribution of spill
Release Source
2. Chemical character of spill
3. Transport characteristics
Residual
LNAPL
Water Table
“Stuck”
NAPL
q
Water Table
Dissolved
Phase
q
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5
Oil Products Vary Hugely in Physical Character
Heavy Fuel & Crude Oils
Light Oils
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6
Inherent Mobility of Different Products to Water
100
Parameter Value
10
1
Viscosity (cP)
0.1
Density (g/cc)
Mobility Factor
il
O
de
C
ru
Fu
el
O
il
#4
Fu
el
O
il
#2
l#
2
D
ie
se
-5
JP
&
4
JP
-
N
ap
th
a
G
as
ol
in
e
0.01
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Effective NAPL Conductivity (cm/sec)
Effective NAPL Conductivity
Gasoline
Diesel
Oil
10 -2
10 -3
10 -4
K ' kr ki
Df g
µf
10 -5
10 -6
10 -7
10 -8
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
NAPL Saturation
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8
Each Has Significantly Differing Chemistry
Jet A
Gasoline
Diesel
Motor Oil
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9
What the Heck Does All that Mean?
• Each product will behave differently
– Physically & chemically
• Each has a different relevance
– Different fate & transport
– Different receptor implications
– Different cleanup implications
• But, NAPL is often treated uniformly
– From a reaction point of view
• Remove it from the ground
– And expectations tend to be uniform
• All that is out of step with realities
– Physical & chemical
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10
Comparative Lateral LNAPL Migration
Gasoline
Large
Medium
Small
Diesel
Large
Medium
Diesel
Heavy
Oil
Silty Sand
Gasoline
Heavy
Oil
Sand
(converse is true for vertical migration)
Small
Large
Medium
Small
Large
Medium
Small
Large
Medium
Small
Large
Medium
Small
140
130
120
110
100
90
80
70
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
Meters from Release
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11
Relative Mobility & Mass Comparison
Silty Sand
Clean Sand
1.E+00
Relative Mass
Relative K
Relative Mass or Conductivity
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
Gasoline Gasoline Gasoline
0.5m
1m
2m
Diesel
0.5m
Diesel 1m Diesel 2m Gasoline Gasoline Gasoline
0.5m
1m
2m
Diesel
0.5m
Diesel 1m Diesel 2m
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Chemistry Contrasts & Flux Magnitude
12
(for same LNAPL & geologic conditions)
Chemical Compound:
MTBE @ 2%
Benzene @ 2%
Xylenes @ 7.5%
Fluorenes @ 2%
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13
Cumulative Mass Loss Comparisons
(combined water/vapor mass loss into environment)
1.E+04
1.E+03
Silty Sand - Gasoline Benzene Lost
Silty Sand - Gasoline Toluene Lost
Clean Sand - Gasoline Benzene Lost
Clean Sand - Gasoline Toluene Lost
Silty Sand - Diesel Benzene Lost
Silty Sand - Diesel Toluene Lost
Clean Sand - Diesel Benzene Lost
Clean Sand - Diesel Toluene Lost
Mass Loss (kg)
1.E+02
1.E+01
1.E+00
1.E-01
1.E-02
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
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14
How Does All that Stack Up Technically?
• Heavier oils are far less risk
– Though light oils may also pose no risk
– And any oil can be a risk in certain cases
• Gasoline is much more mobile
– ~10x more than diesel
– ~ 100s - 1000s times more than heavier oils
• Fuel oils present much lower mass fluxes
– Much less loading to the environment
– 100s to many 1000s times less risk
• In total, these contrasts are on different
playing fields
– Why is our management on the same one?
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15
LNAPL Management Considerations
• Tend to focus on LNAPL mobility evaluations
–
–
–
–
Weight of evidence
Residual saturations
Site specific mobility calculations
Inherent mobility (bail-down & tech evaluations)
• LNAPL plumes stabilize with time as saturations
decrease
• Residual LNAPL as secondary source
– Dissolved Phase / Vapor Phase
• Incorporate risk-based principles
– risk magnitude / risk longevity
– Risk reduction
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16
Business Considerations
• LNAPL liability issues (ex. SOX)
– Financial statements
– Third party disclosure
• Establish LNAPL liability management policy
– How to define?
– Environmental approach (tier 1, 2, 3)
– Accounting approach
• Demonstrate LNAPL liabilities are under control
– How to measure ?
• Manage ongoing LNAPL assessment/remediation
– Portfolio approach
– Reduction in overall liability
– Fiscally sustainable and responsible
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17
Enhanced LNAPL Management Strategy
• Characterize site(s) to delineate extend of LNAPL
(and associated) impacts
– including LNAPL chemistry
• Confirm stability of LNAPL plumes and
associated impacts
– Technically defensible
– Identify trans-boundary and receptor/pathway
concerns
• Evaluate and rank LNAPL site(s) on a risk basis
– Strategic portfolio management
– Be aware of other drivers (real estate)
• Manage Expenditures
– Focus on high risk/high liability sites
– Cash flow and annual budget considerations
– External and internal economic factors
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18
LNAPL Summary
• Physical properties of product are directly related to
hydrocarbon mobility and related risk factors
– True for all ‘phases’ of impact
– Ex. Gasoline greater concern than Diesel
• Strategic management of LNAPL sites incorporating riskbased approaches direct remedial/management effort to
greatest risk/liability reduction
– Maximize effective $$
• Critical to distinguish between product types
when evaluating and managing LNAPL sites.
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