1. UNEXPECTED VOCS IN SOIL GAS ASSESSMENT RESULTS James M. Harless, PhD, CHMM Vice President / Principal Cheryl Kehres-Dietrich, CGWP Principal Paul Roberts Project Geologist

2. OVERVIEW Study questions Methodology Soil gas compositions Soil gas compositions compared to soil and groundwater data Soil vapor criteria exceedances Conclusions

3. STUDY QUESTIONS What were the range and average number of soil gas detections across all projects reviewed? Did it matter which lab performed the analyses? Did it matter what type of site the samples were collected from? How often were compounds detected in soil gas and also soil and/or groundwater (GW)? How often were soil gas criteria exceeded? Were soil and groundwater VI criteria exceedances indicators of soil gas impacts?

4. METHODOLOGY

5. STUDY COMPONENTS 42 Sites 375 Soil Gas Samples 3 States3 Labs “Lab 1” “Lab 2” “Lab 3”

6. PROJECT CATEGORIES Type Of Site MFX = auto parts, tool & die, foundry, cardboard box/paper, etc. OTHER = other commercial, dump, etc. Laboratory

7. SAMPLE COLLECTION Soil gas samples were collected from both sub- slab and deep (typically ≥ 5’) locations o mostly Bottle-Vac ® containers in Michigan o mostly Summa ® canisters in Indiana and Ohio Soil samples were obtained from soil borings Groundwater samples were obtained from temporary or permanent monitoring wells

8. CHEMICAL ANALYSES Soil gas samples were analyzed for VOCs using EPA Method TO-15 Soil and groundwater samples were analyzed for VOCs using EPA Method 8260

9. TYPICAL TO-15 ANALYTES

10. TO-15 (soil gas) vs 8260 (soil / GW) Varies by lab

11. FINDINGS

12. What did we find in the soil gas samples?

13. TYPICALLY, A LOT OF COMPOUNDS Number detected: 8 – 35 (~60 analytes) Average detected: 17 Most frequently detected (≥ 25): Acetone, Benzene, 2-Butanone, Carbon Disulfide, Cyclohexane, Dichlorodifluoromethane, Ethylbenzene, n-Hexane, n-Heptane, PCE, Toluene, TCE, Xylenes Least frequently detected (≤ 2): Bromomethane, Dichlorobenzenes, 1,2-Dichloroethane, 1,1- Dichloroethene, 1,4-Dioxane, MTBE, 1,1,2,2-Tetrachloroethane, 1,1,2- Trichloroethane, 1,1,2-Trichlorofluoroethane, Vinyl Acetate

14. DETECTIONS BY LABORATORY = Average

15. DETECTIONS BY SITE TYPE = Average

16. How did soil gas results compare with soil / GW results?

17. SOIL GAS vs. SOIL / GW SAMPLES Number of analytes detected o Soil gas: 8 – 35 (~60 analytes) o Soil / GW: 0 - 12 Average number of analytes detected o Soil gas: 17 o Soil / GW: 6

18. SOIL GAS vs. SOIL / GW RESULTS

19. Most consistently detected in both Ethylbenzene, Naphthalene, PCE, Toluene, Xylenes Most inconsistent (in soil gas, not soil / GW) Acetone, Benzene, 2-Butanone, Carbon Disulfide, Cyclohexane, Dichlorobenzenes, n-Hexane, Isopropanol, 4-Methyl-2-pentanone, Styrene, Trichlorotrifluoroethane Most inconsistent (in soil gas, rarely in soil / GW) Ethanol, 4-Ethylbenzene, Methylene Chloride, Propylene, THF, 1,1,1-TCA

20. SOIL GAS vs. ASSESSMENT SAMPLES Most inconsistent (in soil / GW, not soil gas) Acetone, Benzene, TMBs

21. Now, what about the concentrations of contaminants in soil gas vs. VI exposure criteria?

22. DETECTIONS vs. EXCEEDANCES 644 detections 35 exceedances ~5% of detected compounds exceeded criteria Exceedances occurred at ~60% of sites

23. THE 5%ers

24. TCE AND PCE MOST PREVALENT

25. What about soil / GW concentrations as indicators of soil gas VI exposure criteria exceedances?

26. THE STATS (NUMBER OF SITES) Exceedances in soil/GW and in soil gas: 17 of 26 (65%) Exceedances in soil gas and in soil/GW: 17 of 19 (89%) Exceedances as unreliable indicators of exceedances in other media: 11 of 28 (39%) Sites with soil/GW criteria exceedances: 26 Sites with soil vapor criteria exceedances: 19

27. WHAT ABOUT THE MEDIUM AS INDICATOR? On a project basis, how often did soil and GW indicate soil gas exceedances? Soil impact was an accurate indicator of VI concern 62% of the time soil > VI screening criteria GW impact was an accurate indicator of VI concern 77% of the time GW > VI screening criteria

28. WHAT ABOUT THE COMPOUND AS INDICATOR? Overall good trackers Overall poor trackers

29. CONCLUSIONS

30. SOIL GAS COMPOSITION

32. SOIL GAS COMPOSITION SOURCES?

33. SOIL GAS COMPOSITION

34. CORRELATION OF SOIL/GW AND SOIL GAS This is consistent with relative mobility and biodegradation (REDOX) potential

35. UNEXPECTED VOCS IN SOIL GAS ASSESSMENT RESULTS James M. Harless, PhD, CHMM Vice President / Principal