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

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

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?

METHODOLOGY

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

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

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

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

TYPICAL TO-15 ANALYTES

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

FINDINGS

What did we find in the soil gas samples?

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

DETECTIONS BY LABORATORY = Average

DETECTIONS BY SITE TYPE = Average

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

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

SOIL GAS vs. SOIL / GW RESULTS

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

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

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

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

THE 5%ers

TCE AND PCE MOST PREVALENT

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

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

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

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

CONCLUSIONS

SOIL GAS COMPOSITION

SOIL GAS COMPOSITION SOURCES?

SOIL GAS COMPOSITION

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

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