Environmental forensics for methane source identification

Use of Forensics to Identify
Sources of Methane
Presented by: Court Sandau, PhD, PChem
November 15, 2007
1
Air and Waste Management Association’s
Vapour Intrusion – A Rapidly Developing Environmental Challenge

Environmental Forensic Investigation
“The application of scientific methods used to
identify the origin and timing of a contaminant
release”
www.chemistry-matters.com
2

When to use Environmental Forensics
• When contamination may not
be yours (remove liability)
• When contamination is from
multiple sources (share
liability)
3

Implicate or Vindicate?
• It may demonstrate your own
responsibility
• It may show dual responsibility
(share the liability)
• It may vindicate a party
completely
4

Issues of Concern
The client (municipality) has identified fugitive
methane gas in the subsurface soils of several
different areas of the city
• Unknown source
• Concerned residents
• Possible health risks
• Potential legal action
5

Health Region Guidelines
Subsurface Action Levels
• Immediate building evacuation, call 911
• Further investigation
• Alarm, ventilation system, evacuation
plan for nearby buildings
• Evaluation of indoor levels
• Source removal or ventilation system
• Monitoring, ventilation recommended
50,000
(100% LEL)
5,000
1,000
0
Indoor Methane
Concentration
(ppm)
6

Forensic Geo-Gas Investigation (FGI)
• Collect gas samples
from various origins
• Characterize each
source and create a
reference library
• Establish the
composition and
source of the fugitive
gases through
comparisons with the
reference library
7

Forensic Geo-gas Investigation
Multidisciplinary Approach to develop lines of
evidence
Witness and knowledgeable individuals Area of highest
Measurement and interpretation of
physical and chemical sampling data
Historical documents
confidence
8

Witness and Knowledgeable
Individuals
• Interview
knowledgeable people
regarding
circumstances
surrounding events
and non-events
9

Historical Documents
10

Measurement and Interpretation
Retention Time
Relative Response
S
S
11

Case History
1963:
nuisance ground
operation closed
Pre 1940’s 1950’s 1960’s 1970’s 1980’s 1990’s 2000’s
1953:
nuisance ground
operation began
2001-2005:
Phase I&II Site
Investigations
indicate elevated
CH4 Levels
Borrow
Pit/
Natural
Vegetation
12

Investigation
• Sampling location chosen based on historical data
• 1L gas samples taken from 4 sample locations
• Tiered Forensic Approach adopted to identify
potential sources
13

Tiered Forensic Approach
Calorific Value (BTU Ft3)
Hydrocarbon Content
Volatile Organic Carbon Content
Level 1
Fixed Gas
Radio Active Isotope (14C)
Stable Isotope Analysis of CH4
Level 2
14

QA-QC
• Duplicate sample collected at reference library
sampling point
• Relative Percent Differences <20% indicates good
precision
• Lab reported accuracy to within 2% of reference
standards
15

Results
Level 1: Fixed Gas
Methane and Fixed Gas Data Library
100
90
80
70
60
50
40
30
20
10
0
Historic Landfill
Landfill
Landfill
Sewage
Sewage
Natural Gas
Natural Gas
Unknown #1
Unknown #2
Sampling Location
Volume (%)
O2 %
CO2 %
N2 %
CH4%
16

Results
Level 1: Hydrocarbon Fingerprinting
60
50
40
30
20
10
0
C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15
Alkane
s
Concentration mg/m3
Natural Gas
17

Results
60
50
40
30
20
10
0
C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15
Alkanes
Concentration mg/m3
Landfill
18

Results
60
50
40
30
20
10
0
C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15
Alkanes
Concentration mg/m3
Sewage
19

Results
60
50
40
30
20
10
0
C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15
Alkanes
Concentration mg/m3
Unknown #1
20

Results
60
50
40
30
20
10
0
C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15
Alkanes
Concentration mg/m3
Unknown #2
21

Results
22

Results
Level 1: VOC Fingerprinting
60
50
40
30
20
10
0
Volatile Organic Compounds
Concentration mg/m3
Natural Gas: Alkanes
and Alkenes
23

Results
60
50
40
30
20
10
0
Concentration mg/m3
Sewage: Sulfide
Compounds
24

Results
60
50
40
30
20
10
0
Concentration mg/m3
Landfill: Chlorinated
Compounds
25

Results
60
50
40
30
20
10
0
Concentration mg/m3
Unknown #1
26

Results
60
50
40
30
20
10
0
Concentration mg/m3
Unknown #2
27

Summary of Level 1 Findings
• 2 locations had elevated levels of CH4
• Based on calorific and fixed gas data
Thermogenic sources were ruled out
• Unable to differentiate landfill, sewage sources
using level 1 investigation
• Need to progress to Level 2
28

Radio Carbon Isotope Dating 14C
•Naturally occurring isotope with a half life of
5730 yrs
•The ratio of 14C contained within CH4 is indicative
of age
50%
Age 5730 yr
100%
Age 0
……
.
25%
Age 11,460 yr
Natural Gas Landfill Sewage Unknown
14C (pMc) 0 >100 100-110 141
29

Stable Isotope Analysis
99
%
pp
ee--
Hydrogen,1H
nn
~1
%
pp
ee--
DDeeuutteerriiuumm,,22HH,, DD
<1
%
pp nn
nn
ee--
TTrriittiiuumm,,33HH,, TT
• Highly variable in nature and generally endemic of every
organic compound
• Have been used with petroleum exploration for many
decades, advance is isotope techniques has led to new
areas of applications e.g. archaeology, biomedical
sciences, biosynthesis and environmental forensics
30

Clarke Diagram for 2D Fingerprinting
d13C-CH4 (‰)
Bacterial MF
d2H-CH4 (‰)
Bacterial
Carbonate
Reduction
Bacterial
Mix and
Transition
Early Mature
Thermogenic
migration
Bacterial Oxidation
31

Combination of Techniques
Unknown
Landfill
Migration will cause a change in methane
concentration but not a large isotopic shift
d13C-CH4 (‰)
C1/[C2+C3]
Sewage
Plant
Sewage
Plant
Unknown
Landfill
Historic
Landfill
Natural Gas
Natural Gas
Bacterial consumption of Methane will cause a
reduction in Methane concentration and
isotopic shift
Migration
Oxidation
Migration
32

Summary
Source
Calorifi
c Value
(BTU/Ft
3)
Level 1 Level 2
CH4/CO
2
GC Carbon
Analysis VOC 14C –
pMC δ13C and δ2H of CH4
Thermogenic ~ 1000 + CH4 Low C1 /C1 – C5 Odorants 0 pMC δ13C = -48‰ to -40‰
δ2H = -250‰ to -200‰
Landfill ~600
CO2 =
CH4
High C1 /C1 – C5
chlorinated
compounds
>100
pMC
δ13C = -60‰ to -52‰
δ2H = -400‰ to
-350‰
Sewage ~600
CO2 =
CH4
High C1 /C1 – C5
Sulphur
containing
100
-110
pMC
δ13C = -52‰ to -48‰
δ2H = -425‰ to
-375‰
Unknown1 ~447
CO2<
CH4
High C1 /C1 – C5 ND 141
pMC
δ13C = -54.5‰
δ2H = -346‰
Unknown2 ~26
CO2 =
CH4
High C1 /C1 – C5 ND 101
pMC
δ13C = -51.5‰
δ2H = -341‰
www.chemistry-matters.com 33

Summary
Source
Calorifi
c Value
(BTU/Ft
3)
Level 1 Level 2
CH4/CO
2
GC Carbon
Analysis VOC 14C –
pMC δ13C and δ2H of CH4
Thermogenic ~ 1000 + CH4 Low C1 /C1 – C5 Odorants 0 pMC δ13C = -48‰ to -40‰
δ2H = -250‰ to -200‰
Landfill ~600
CO2 =
CH4
High C1 /C1 – C5
chlorinated
compounds
>100
pMC
δ13C = -60‰ to -52‰
δ2H = -400‰ to
-350‰
Sewage ~600
CO2 =
CH4
High C1 /C1 – C5
Sulphur
containing
100
-110
pMC
δ13C = -52‰ to -48‰
δ2H = -425‰ to
-375‰
Unknown1 ~447
CO2<
CH4
High C1 /C1 – C5 ND 141
pMC
δ13C = -54.5‰
δ2H = -346‰
Unknown2 ~26
CO2 =
CH4
High C1 /C1 – C5 ND 101
pMC
δ13C = -51.5‰
δ2H = -341‰
Potentially a mixed source
34

Conclusion
• Main Issue for client was identification of potential sources of
fugitive methane emissions
• Outcomes
– Generation of Library
– Use of historical data and Level 1 analysis eliminated
thermogenic sources
– Level 2 data indicate degradation of landfill material may be
responsible for methane found at sampling point with highest
concentration
– Second sampling point likely to be of a mixed source with landfill
and organic soils contributing
• Further monitoring may determine the fate and behavior of
elevated methane which will help clients to make decision
regarding any action needed
35

Environmental forensics for methane source identification

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