Methane forensics techniques for source allocation
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The document discusses using forensic techniques to identify sources of fugitive methane found in subsurface soils in a municipality. Level 1 analysis using fixed gas composition, hydrocarbon fingerprinting, and VOC analysis ruled out thermogenic sources but could not differentiate between landfill and sewage sources. Level 2 analysis using carbon dating, and stable isotope analysis of methane indicated one sampling point was likely degrading landfill material and another was a mixed source of landfill and organic soils. The analysis identified potential methane sources to help the client determine appropriate actions.
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Methane forensics techniques for source allocation
- 1. Use of Forensics to Identify Sources of Methane Presented by: Court Sandau, PhD, PChem November 15, 2007 Air and Waste Management Association’s Vapour Intrusion – A Rapidly Developing Environmental Challenge 1 © 2015 Chemistry Matters Inc.
- 2. Environmental Forensic Investigation “The application of scientific methods used to identify the origin and timing of a contaminant release” www.chemistry-matters.com 2© 2015 Chemistry Matters Inc.
- 3. When to use Environmental Forensics • When contamination may not be yours (remove liability) • When contamination is from multiple sources (share liability) www.chemistry-matters.com 3© 2015 Chemistry Matters Inc.
- 4. Implicate or Vindicate? • It may demonstrate your own responsibility • It may show dual responsibility (share the liability) • It may vindicate a party completely www.chemistry-matters.com 4© 2015 Chemistry Matters Inc.
- 5. 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 www.chemistry-matters.com 5© 2015 Chemistry Matters Inc.
- 6. Health Region Guidelines Subsurface Action Levels • Further investigation • Evaluation of indoor levels • Source removal or ventilation system • Further investigation • Monitoring, ventilation recommended • Immediate building evacuation, call 911 • Further investigation • Alarm, ventilation system, evacuation plan for nearby buildings 50,000 (100% LEL) Indoor Methane Concentration (ppm) 5,000 1,000 0 www.chemistry-matters.com 6© 2015 Chemistry Matters Inc.
- 7. 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 www.chemistry-matters.com 7© 2015 Chemistry Matters Inc.
- 8. Forensic Geo-gas Investigation Multidisciplinary Approach to develop lines of evidence Measurement and interpretation of physical and chemical sampling data Historical documents Witness and knowledgeable individuals Area of highest confidence www.chemistry-matters.com 8© 2015 Chemistry Matters Inc.
- 9. Witness and Knowledgeable Individuals • Interview knowledgeable people regarding circumstances surrounding events and non-events www.chemistry-matters.com 9© 2015 Chemistry Matters Inc.
- 10. Historical Documents www.chemistry-matters.com 10© 2015 Chemistry Matters Inc.
- 11. Measurement and Interpretation Retention Time RelativeResponse S S www.chemistry-matters.com 11© 2015 Chemistry Matters Inc.
- 12. Case History Pre 1940’s 1950’s 1960’s 1970’s 1980’s 1990’s 2000’s 1953: nuisance ground operation began 1963: nuisance ground operation closed 2001-2005: Phase I&II Site Investigations indicate elevated CH4 Levels Borrow Pit/ Natural Vegetation www.chemistry-matters.com 12© 2015 Chemistry Matters Inc.
- 13. Investigation • Sampling location chosen based on historical data • 1L gas samples taken from 4 sample locations • Tiered Forensic Approach adopted to identify potential sources www.chemistry-matters.com 13© 2015 Chemistry Matters Inc.
- 14. Tiered Forensic Approach Calorific Value (BTU Ft3 ) Hydrocarbon Content Volatile Organic Carbon Content Level1 Fixed Gas Radio Active Isotope (14 C) Stable Isotope Analysis of CH4 Level2 www.chemistry-matters.com 14© 2015 Chemistry Matters Inc.
- 15. 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 www.chemistry-matters.com 15© 2015 Chemistry Matters Inc.
- 16. Level 1: Fixed Gas Results Methane and Fixed Gas Data Library 0 10 20 30 40 50 60 70 80 90 100 H istoric Landfill Landfill Landfill Sew age Sew age N aturalG as N aturalG as U nknow n #1 U nknow n #2 Sampling Location Volume(%) O2 % CO2 % N2 % CH4% www.chemistry-matters.com 16© 2015 Chemistry Matters Inc.
- 17. Level 1: Hydrocarbon Fingerprinting Results 0 10 20 30 40 50 60 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Alkane s Concentrationmg/m3 Natural Gas www.chemistry-matters.com 17© 2015 Chemistry Matters Inc.
- 18. Level 1: Hydrocarbon Fingerprinting Results 0 10 20 30 40 50 60 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Alkanes Concentrationmg/m3 Landfill www.chemistry-matters.com 18© 2015 Chemistry Matters Inc.
- 19. Level 1: Hydrocarbon Fingerprinting Results 0 10 20 30 40 50 60 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Alkanes Concentrationmg/m3 Sewage www.chemistry-matters.com 19© 2015 Chemistry Matters Inc.
- 20. Level 1: Hydrocarbon Fingerprinting Results 0 10 20 30 40 50 60 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Alkanes Concentrationmg/m3 Unknown #1 www.chemistry-matters.com 20© 2015 Chemistry Matters Inc.
- 21. Level 1: Hydrocarbon Fingerprinting Results 0 10 20 30 40 50 60 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 Alkanes Concentrationmg/m3 Unknown #2 www.chemistry-matters.com 21© 2015 Chemistry Matters Inc.
- 22. Level 1: Hydrocarbon Fingerprinting Results www.chemistry-matters.com 22© 2015 Chemistry Matters Inc.
- 23. Level 1: VOC Fingerprinting Results 0 10 20 30 40 50 60 Volatile Organic Compounds Concentrationmg/m3 Natural Gas: Alkanes and Alkenes www.chemistry-matters.com 23© 2015 Chemistry Matters Inc.
- 24. Level 1: VOC Fingerprinting Results 0 10 20 30 40 50 60 Volatile Organic Compounds Concentrationmg/m3 Sewage: Sulfide Compounds www.chemistry-matters.com 24© 2015 Chemistry Matters Inc.
- 25. Level 1: VOC Fingerprinting Results 0 10 20 30 40 50 60 Volatile Organic Compounds Concentrationmg/m3 Landfill: Chlorinated Compounds www.chemistry-matters.com 25© 2015 Chemistry Matters Inc.
- 26. Level 1: VOC Fingerprinting Results 0 10 20 30 40 50 60 Volatile Organic Compounds Concentrationmg/m3 Unknown #1 www.chemistry-matters.com 26© 2015 Chemistry Matters Inc.
- 27. Level 1: VOC Fingerprinting Results 0 10 20 30 40 50 60 Volatile Organic Compounds Concentrationmg/m3 Unknown #2 www.chemistry-matters.com 27© 2015 Chemistry Matters Inc.
- 28. 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 www.chemistry-matters.com 28© 2015 Chemistry Matters Inc.
- 29. Radio Carbon Isotope Dating 14 C •Naturally occurring isotope with a half life of 5730 yrs •The ratio of 14 C contained within CH4 is indicative of age 50% Age 5730 yr 100% Age 0 … …. 25% Age 11,460 yr Natural Gas Landfill Sewage Unknown 14 C (pMc) 0 >100 100-110 141 www.chemistry-matters.com 29© 2015 Chemistry Matters Inc.
- 30. Stable Isotope Analysis • 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 pp ee-- Hydrogen,1 H nn pp ee-- Deuterium,Deuterium,22 H, DH, D nn pp nn ee-- Tritium,Tritium,33 H, TH, T 99 % ~1 % <1 % www.chemistry-matters.com 30© 2015 Chemistry Matters Inc.
- 31. Clarke Diagram for 2D Fingerprinting δ13 C-CH4(‰) Bacterial MF δ2 H-CH4 (‰) Bacterial Carbonate Reduction Bacterial M ixand Transition Early Mature Thermogenic migration Bacterial Oxidation www.chemistry-matters.com 31© 2015 Chemistry Matters Inc.
- 32. Combination of Techniques δ13 C-CH4 (‰) C1/[C2+C3] Sewage Plant Sewage Plant Unknown Unknown Landfill Landfill Historic Landfill Natural Gas Natural Gas Bacterial consumption of Methane will cause a reduction in Methane concentration and isotopic shift Migration will cause a change in methane concentration but not a large isotopic shift Migration Migration Oxidation www.chemistry-matters.com 32© 2015 Chemistry Matters Inc.
- 33. Summary Source Calorifi c Value (BTU/Ft 3 ) CH4 /CO 2 GC Carbon Analysis VOC 14 C – pMC δ13 C and δ2 H of CH4 Thermogenic ~ 1000 + CH4 Low C1 /C1 – C5 Odorants 0 pMC δ13 C = -48‰ to -40‰ δ2 H = -250‰ to -200‰ Landfill ~600 CO2 = CH4 High C1 /C1 – C5 chlorinated compounds >100 pMC δ13 C = -60‰ to -52‰ δ2 H = -400‰ to -350‰ Sewage ~600 CO2 = CH4 High C1 /C1 – C5 Sulphur containing 100 -110 pMC δ13 C = -52‰ to -48‰ δ2 H = -425‰ to -375‰ Unknown1 ~447 CO2 < CH4 High C1 /C1 – C5 ND 141 pMC δ13 C = -54.5‰ δ2 H = -346‰ Unknown2 ~26 CO2 = CH4 High C1 /C1 – C5 ND 101 pMC δ13 C = -51.5‰ δ2 H = -341‰ Level 1 Level 2 www.chemistry-matters.com 33© 2015 Chemistry Matters Inc.
- 34. Summary Source Calorifi c Value (BTU/Ft 3 ) CH4 /CO 2 GC Carbon Analysis VOC 14 C – pMC δ13 C and δ2 H of CH4 Thermogenic ~ 1000 + CH4 Low C1 /C1 – C5 Odorants 0 pMC δ13 C = -48‰ to -40‰ δ2 H = -250‰ to -200‰ Landfill ~600 CO2 = CH4 High C1 /C1 – C5 chlorinated compounds >100 pMC δ13 C = -60‰ to -52‰ δ2 H = -400‰ to -350‰ Sewage ~600 CO2 = CH4 High C1 /C1 – C5 Sulphur containing 100 -110 pMC δ13 C = -52‰ to -48‰ δ2 H = -425‰ to -375‰ Unknown1 ~447 CO2 < CH4 High C1 /C1 – C5 ND 141 pMC δ13 C = -54.5‰ δ2 H = -346‰ Unknown2 ~26 CO2 = CH4 High C1 /C1 – C5 ND 101 pMC δ13 C = -51.5‰ δ2 H = -341‰ Level 1 Level 2 Potentially a mixed source www.chemistry-matters.com 34© 2015 Chemistry Matters Inc.
- 35. 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 www.chemistry-matters.com 35© 2015 Chemistry Matters Inc.
- 36. Contact Info: Chemistry Matters Inc. Court Sandau Cell: 1.403.669.8566 Email: csandau@chemistry-matters.com URL: chemistry-matters.com Twitter: @Chem_Matters Slideshare: www.slideshare.net/csandau © 2015 Chemistry Matters Inc.