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Environmental forensics for methane source identification

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Presentation from 2007 to AWMA conference on vapour intrusion. Presentation covers the environmental forensics investigation of gases to identify the sources of the potential vapour intrusion. Techniques used both standard gas analysis as well as isotopic analysis of selected gases to identify the likely sources.

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Environmental forensics for methane source identification

  1. 1. 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
  2. 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
  3. 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
  4. 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
  5. 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
  6. 6. Health Region Guidelines Subsurface Action Levels • Immediate building evacuation, call 911 • Further investigation • Alarm, ventilation system, evacuation plan for nearby buildings • Further investigation • Evaluation of indoor levels • Source removal or ventilation system • Further investigation • Monitoring, ventilation recommended 50,000 (100% LEL) 5,000 1,000 0 Indoor Methane Concentration (ppm) www.chemistry-matters.com 6
  7. 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
  8. 8. 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 www.chemistry-matters.com 8
  9. 9. Witness and Knowledgeable Individuals • Interview knowledgeable people regarding circumstances surrounding events and non-events www.chemistry-matters.com 9
  10. 10. Historical Documents www.chemistry-matters.com 10
  11. 11. Measurement and Interpretation Retention Time Relative Response S S www.chemistry-matters.com 11
  12. 12. 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 www.chemistry-matters.com 12
  13. 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
  14. 14. 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 www.chemistry-matters.com 14
  15. 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
  16. 16. 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% www.chemistry-matters.com 16
  17. 17. 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 www.chemistry-matters.com 17
  18. 18. 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 Alkanes Concentration mg/m3 Landfill www.chemistry-matters.com 18
  19. 19. 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 Alkanes Concentration mg/m3 Sewage www.chemistry-matters.com 19
  20. 20. 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 Alkanes Concentration mg/m3 Unknown #1 www.chemistry-matters.com 20
  21. 21. 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 Alkanes Concentration mg/m3 Unknown #2 www.chemistry-matters.com 21
  22. 22. Results Level 1: Hydrocarbon Fingerprinting www.chemistry-matters.com 22
  23. 23. Results Level 1: VOC Fingerprinting 60 50 40 30 20 10 0 Volatile Organic Compounds Concentration mg/m3 Natural Gas: Alkanes and Alkenes www.chemistry-matters.com 23
  24. 24. Results Level 1: VOC Fingerprinting 60 50 40 30 20 10 0 Volatile Organic Compounds Concentration mg/m3 Sewage: Sulfide Compounds www.chemistry-matters.com 24
  25. 25. Results Level 1: VOC Fingerprinting 60 50 40 30 20 10 0 Volatile Organic Compounds Concentration mg/m3 Landfill: Chlorinated Compounds www.chemistry-matters.com 25
  26. 26. Results Level 1: VOC Fingerprinting 60 50 40 30 20 10 0 Volatile Organic Compounds Concentration mg/m3 Unknown #1 www.chemistry-matters.com 26
  27. 27. Results Level 1: VOC Fingerprinting 60 50 40 30 20 10 0 Volatile Organic Compounds Concentration mg/m3 Unknown #2 www.chemistry-matters.com 27
  28. 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
  29. 29. 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 www.chemistry-matters.com 29
  30. 30. 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 www.chemistry-matters.com 30
  31. 31. Clarke Diagram for 2D Fingerprinting d13C-CH4 (‰) Bacterial MF d2H-CH4 (‰) Bacterial Carbonate Reduction Bacterial Mix and Transition Early Mature Thermogenic migration Bacterial Oxidation www.chemistry-matters.com 31
  32. 32. 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 www.chemistry-matters.com 32
  33. 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‰ www.chemistry-matters.com 33
  34. 34. 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 www.chemistry-matters.com 34
  35. 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

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