Chemical Fingerprinting of
Groundwater Plumes:
Concepts and Case Studies
David S. Lipson, CPG
Blasland, Bouck & Lee, Inc.
Golden, CO
Premise
• Sources of chemicals impart unique physicalchemical characteristics (also known as
“fingerprints”) on the chemicals.
• When chemicals are released and contaminate
environments (e.g., air, groundwater), their
fingerprints can be used to help establish the
timing of the release and allocate between
different sources in many cases.
Outline
• Situations where chemical fingerprinting of
groundwater plumes may be useful
• Fingerprinting methods:
1.
2.
3.
Concentration ratios
Isotopes
Single, or unique chemicals
• Strengths and weaknesses
• Case studies
One Situation Where Fingerprinting May Be
Useful: Co-Mingled Plumes From Multiple
Sources
Oil
Terminal
A
Pipelines
Oil
Terminal
B
Oil
Terminal
C
A Second Situation Where Fingerprinting
May Be Useful: Co-Mingled Plume From A
Single Source
Big
Defense
Contractor
Ongoing
Release
From Mid-80s
Late 70’s
Release
60s
Release
Chemical Concentration Ratios
• Used when chemical mixtures are present in a plume, which includes
most contaminant plumes of interest.
• Most chemical sources involve mixtures. For example:
– Gasoline and other petroleum fuels (100s of compounds)
– Coal tar and creosote (100s of compounds)
– Solvents (multiple solvents often used)
– Acid mine drainage (multiple metals often present)
– Dielectric fluids (PCBs are mixtures of many congeners)
• It is rare when a single chemical is released to the environment due
to widespread use of chemical mixtures, chemical additives, and
impurities.
• Even if a single chemical were released to the environment, in many
cases chemicals degrade forming intermediate byproducts that add
to the chemical mixture.
Chemical Concentration Ratios:
Transport of a Two-Component Solvent Mixture
Two-Component Fate and Transport Model
00 days
feet
500
500 days
feet
1000feet
days
1000
1500 feet
days
1500
2000
2000days
feet
TCE
TCA
3000
3000days
feet
4000 days
4000 feet
5000
5000 days
feet
6000 days
6000
feet
Groundwater velocity = 240 ft/yr
TCE retardation
= 2.3
TCA retardation
= 2.6
No degradation
Conclusion: Fingerprint changes with
time and distance due to retardation.
Chemical Concentration Ratios:
Transport of a Three-Component Solvent Mixture
Conclusion: Fingerprint changes with time and distance due to degradation
Three-Component Fate and Transport Model
0 days
0 feet
250
250days
feet
500 days
500 feet
750 days
750 feet
1000 days
1000 feet
PCE
TCE
1500 days
1500 feet
2000 days
2000 feet
TCA
2500 days
2500 feet
3000feet
days
3000
Groundwater velocity = 240 ft/yr
No retardation
Solvents degrade:
PCE half life
= 4 yrs
TCE half life
= 8 yrs
TCA half life
= 2 yrs
Conclusion: Fingerprint changes with
time and distance due to degradation.
State of Arkansas vs. Diamond Lakes Oil Co.
Contaminated
Residence
Diamond Lakes Oil Co.
(Station A)
MW5-5R
Station B
GW Flow
Direction
Ternary Diagram Showing Concentration Ratios of Benzene, Toluene, and Xylenes
From All Groundwater Samples Collected at Station A and Station B Monitor Wells
100 % Benzene
25
MW-5/5R
50
100% Xylenes
25
50
50
Station A Groundwater Samples (N = 121)
Station B Groundwater Samples (N = 62)
Fresh Gasoline
100% Toluene
Ternary Diagram Showing BTX Concentration Ratios - June 1998 Data
100% Benzene
J
1
Circle Size Indicates Total
BTX Concentration
< 1 ppm
2
1 - 10 ppm
25
> 10 ppm
50
50
L
Fresh Gasoline
5
NK
F
M
4 6
H
E
100% Xylenes
3
25
50
100% Toluene
Station A Groundwater Samples (N = 11; non-detects not shown)
Station B Groundwater Samples (N = 6)
Ternary Diagram Showing BTX Concentration Ratios - June 1999 Data
100% Benzene
Circle Size Indicates Total
BTX Concentration
O
1
< 1 ppm
2
1 - 10 ppm
25
J
> 10 ppm
K
L
50
50
Fresh Gasoline
N
5
F
I
E
4
M
DH
100% Xylenes
6
25
3
50
100% Toluene
Station A Groundwater Samples (N = 11)
Station B Groundwater Samples (N = 6)
Ternary Diagram Showing BTX Concentration Ratios - August 1999 Data
100% Benzene
O
2
Circle Size Indicates Total
BTX Concentration
< 1 ppm
1
1 - 10 ppm
25
> 10 ppm
K
N
L
50
50
Fresh Gasoline
F
D
J
5
I
MH
4 6
E
100% Xylenes
3
25
100% Toluene
50
Station A Groundwater Samples (N = 11)
Station B Groundwater Samples (N = 6)
Ternary Diagram Showing BTX Concentration Ratios – MW5/MW-5R With Time
100 % Benzene
Circle Size Indicates Total
BTX Concentration
< 1 ppm
1/99
4/99
1 - 10 ppm
25
> 10 ppm
50
50
Fresh Gasoline
6/98
4/00
8/99 6/99
2/00
6/00
100 % Xylenes
25
UST Excavation (Station B)
8/00
12/99
50
100% Toluene
Station B groundwater samples from MW-5/MW-5R
State of Arkansas vs. Diamond Lakes Oil Co.
Findings of the Case:
• Concentration ratios demonstrated that gasoline chemicals from Station B
had a fingerprint different than gasoline chemicals from Station A.
• The BTX concentration ratios also showed that fresh releases (slugs) of
gasoline were emanating from Station B.
• The jury found in Station A’s favor, awarding damages of $300,000.
• The ruling, and expert testimony, survived on appeal to the Supreme Court
of Arkansas.
Chemical Isotopes
Nuclear Structure of Atoms: Protons and neutrons
• Protons = atomic number
• Protons + neutrons = atomic weight
Isotopes: Different forms of the same element that have
the same atomic number but different molecular weights.
Example: Oxygen
• Most oxygen atoms have 8 protons and 8 neutrons
Atomic weight 16:
16O
• About 0.2% of oxygen atoms have 10 neutrons
Atomic weight 18:
18O
• About 0.04% of oxygen atoms have 9 neutrons
Atomic weight 17:
17O
Chemical Isotopes
Molecular weight is important in environmental studies
because it influences the fate and transport of chemicals
Example: Evaporation of water
Chemical Isotopes
Vapor in Cloud
d O = -21 per mil
18
Vapor in Cloud
d O = -12 per mil
18
Snow
d O = -11 per mil
18
Rain
d O = -3 per mil
18
Continent
Ocean
d18 O = 0 per mil
Chemical Isotopes
Stable chemical isotopes useful in environmental forensics:
Chemical
Isotope
Ratio
13C
13C
2H
2H
Oxygen
18O
Chlorine
37Cl
Carbon
Hydrogen
Natural Abundance (%)
/ 12C
1.11
/ 1H
0.015
18O
/ 16O
0.204
37Cl
/ 35Cl
Sulfur
34S
34S
/ 32S
Bromine
81Br
81Br
/ 79Br
24.23
4.21
49.31
There are numerous other isotopes that exist, and can be evaluated
depending on the site-specific application.
Mother Goose and Grimm ©2001 Grimmy, Inc.
Dist. By Tribune Media Services. All rights reserved.
BBL, Inc.
Chemical Isotopes
Because isotopes have different molecular weights, certain
processes can select for different isotopes.
Examples:
• Evaporation selects for lighter isotopes, resulting in heavier
residue.
• Biodegradation reactions select lighter isotopes, resulting in
heavier residue.
• Chemical manufacturing processes can select for different
isotopes
Therefore, these processes can impart a unique isotopic fingerprint
to a chemical plume undergoing transport and degradation in the
environment.
Forensic Isotope Geochemistry
• Standard analytical methods (e.g., GC-IRMS)
allow compound-specific detection of isotopes
at ppm and ppb levels.
• Applications:
• Fingerprint hydrocarbons and solvents
• Identify/allocate sources of pollution
• Examine fate and transport processes
• Evaluate remedial measures
Crude Oil and Refined Products
36D
32D
24D
C35
C34
C33
C32
C31
C30
C29
C28
C27
C26
C25
C24
C23
C22
C21
C20
C19
C18
C17
C15
C16
C14
C13
n -alkanes
-25
-26
-27
13
d C (per mil)
-28
-29
-30
-31
-32
Crude
Crude
Crude
Crude
Crude
-33
-34
-35
Adapted from Mansuy et al., 1997
Oil
Oil
Oil
Oil
Oil
A
B
C
D
E
BTEX in Gasoline Samples
Isotopic composition of individual BTEX compounds
-25
M-1
M-2
M-3
-27
13
d C (per mil)
-26
-28
-29
B
T
E
pX
mX
oX
Chlorinated Solvents
Isotopic composition of solvents from different manufacturers
-25
TCE
TCA
-27
-28
-29
d
13
C (per mil)
-26
-30
-31
Adapted from Shouakar-Stash et al. (2003)
-32
-4
-3
-2
-1
0
1
d37 Cl (per mil)
2
3
4
5
Allocation – 2 Sources
TCE d13C or d37Cl, 2 sources, single tracer
Source A:
d13C -30‰
d37Cl -2‰
Source B:
d13C -25‰
d37Cl +3‰
Plume
d13C -29‰
d37Cl -1‰
Plume = 80% Source A, 20% Source B
Single, or Unique Chemicals That Can Be Used
to Fingerprint Plumes in Some Cases
Gasoline Additives
• Methyl tertiary butyl ether (MTBE)
• Tertiary butyl alcohol (TBA)
• Lead anti-knocks (e.g., tetraethyl lead)
• Talloamines
• 1,2-Dichloroethane (DCA)
Solvent stabilizers
• 1,4-Dioxane
• Dimethyl amine (DMA)
• Tetrahydrofuran (THF)
Others: chrome, nickel, copper
Strengths and Weaknesses Of These
Plume Fingerprinting Methods
Strengths
 Concentration Ratios
 Demonstrative
 Strong visual impact
 Easily explained
 Isotopic Analysis
Weaknesses
 Subject to misapplication
 Success is site-specific
 Proven in court
 Data do not always exist
 Powerful if conditions
permit
 Subject to misapplication &
faulty interpretation
 Excellent where there are  Weathering of compounds
can limit viability
distinct differences in
compounds
 Unique Chemicals
 Demonstrative
 Success is site-specific
 Powerful where present
 Data do not always exist
Conclusions
• The state of the science has progressed
significantly in the past several years to permit
fingerprinting of contamination plumes in many
cases.
• There are several, proven plume fingerprinting
methods that can be used.
• Multiple lines of evidence supporting the same
conclusion provides the strongest position.