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“Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline”

“Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline”. Presented on January 22, 1999 to. Clean Air Act Advisory Committee Panel on Oxygenate Use in Gasoline. Prepared by. John Zogorski, David Bender, Mike Moran, and Mike Halde

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“Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline”

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  1. “Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline” Presented on January 22, 1999 to Clean Air Act Advisory Committee Panel on Oxygenate Use in Gasoline Prepared by John Zogorski, David Bender, Mike Moran, and Mike Halde National Water-Quality Assessment Program U.S. Geological Survey Rapid City, SD (Note: This document contains some provisional water-quality information that may change pending final quality-assurance review)

  2. Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline (John Zogorski, U.S. Geological Survey) 1. Important concepts for understanding the occurrence, behavior and fate of MTBE in ground water 2. Ground-water issues related to MTBE 3. Other oxygenates and by-products 4. Concluding remarks

  3. Estimated Solubility of MTBE in Water at 55 Degrees Fahrenheit Solubility From (mg/L) Pure MTBE 51,200,000 15% v/va MTBE in gasoline 7,700,000 (oxygenated gasoline) 10% v/v MTBE in gasoline 5,100,000 (reformulated gasoline) 1% v/v MTBE in gasoline 510,000 (octane enhanced gasoline) Note: USEPA advisory for drinking water is 20-40 mg/L a v/v -- volume MTBE per volume gasoline

  4. Example of Partitioning of MTBE and 2 Gasoline Hydrocarbons Between the Aquifer Material and Water Ethylbenzene MTBE Benzene Assumptions: solid phase foc = 0.001 n = 0.25 dissolved phase 1 liter of aquifer = 2.0 kg sand + 0.25 kg water Note: The proportion of partitioning for each compound illustrated above will not change with varying organic matter content (foc), however, the total mass of each compound sorbed will be less with lower foc.

  5. Example of Difference in Migration of Water, MTBE and 2 Gasoline Hydrocarbons Elapsed time since release Travel distance (in miles) 2.0 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 Assumptions: continuous point source foc = 0.001 3.3 years n = 0.25 s = 2.65 g/cm3 Ethylbenzene vf = 1 ft/day Benzene isotropic sand MTBE 10 years no biodegradation Water 30 years Note: The proportion of partitioning for each compound will not change with varying organic matter content (foc), however, the chromatographic separation will be less with lower foc.

  6. H C H H H H C C C O H H H H C H H H Biodegradation of MTBE in Ground Water • Stability due to tertiary carbon and ether bond • Low cell yields comparable to anaerobic fermenting bacteria and autotrophs • (Salanitro and others, 1994, Applied and Environmental Microbiology, July, p. 2593-2596.) • OSTP finding: “MTBE degradation is significantly less than BTEX” • Some recent field evidence of biodegradation: • - Schirmer and Barker, 1998, Ground Water Monitoring • and Remediation, Spring, pp. 113-122. • - Borden and others, 1997, Water Resources Research, • vol. 33, no. 5, pp. 1105-1115. • - Baehr and others, 1997, preprints of papers, 213th • ACS National Meeting, vol. 37, no. 1, pp. 417-418. • Geochemical factors and ubiquity of indigenous MTBE degraders are poorly understood

  7. Flow Paths and Contributing Area to a Community Water-Supply Well Discharge Recharge Unsaturated zone Recharge 5 year Isotropic sand 10 year 15 year 20 year 25 year Saturated zone 30 year Cross section Discharging well Contributing area Plan view Regional ground-water flow

  8. MTBE Detection Frequency versus Median Ground-Water Age for Glassboro, N.J. Study Area (Note: based on provisional USGS data) (N = 50) (N = 20) (N = 30) Median Ground-water age Monitoring wells screened near water table Monitoring wells screened at moderate depth Community water- supply wells screened at bottom of aquifer Note: N = number of wells sampled.

  9. Ground Water Issue 1 • Low concentrations of MTBE are • frequently found in ambient ground • water and community water supply • wells in some high MTBE use areas. Note: “ambient ground water” is used to distinguish the sampling completed by the USGS in the National Water-Quality Assessment Program, which describes water-quality conditions spatially for a given aquifer, in contrast to monitoring of highly contaminated ground water done by other agencies at regulated, point-source release sites.

  10. MTBE in Ambient Ground Water of U.S. NAWQA Data (2,743 wells, mix well types, mix of networks, 1993-98 data, 0.2 g/L RL) (Note: based on provisional USGS data) Concentration Frequency Number of (g/L) wells < 0.2 94.7 2,598 0.2 - 20 4.8 133 > 20 0.5 12a a) only 1 well was used for drinking water

  11. Detection of MTBE in Ambient Ground Water (NAWQA data, 1993-98, 0.2 g/L RL) (Note: based on provisional USGS data) • MTBE Use • 21. % detection in high use areas • 2.3% detection in low/no use areas • Detection/Non-Detection Matrix • MTBE Found in GW • MTBE Use Yes No • High use area 92 348 • Low / No use area 53 2,250 • (odds ratio = 11.2) • Other factors are important and need to be controlled • to assess the true effect of high MTBE use on detections • in ambient ground water.

  12. MTBE in Community Water Supply Wells of U.S. (Note: based on provisional USGS data) Number of wells or Source systems with MTBE National LUST Programs 251 to 422 public wells in 19 statesa Survey (1998) OSTP (1997) 51 public water systems in 6 of 7 states that provided informationa 12 Eastern Statesc 55 community systems in 7 states Compilation (1999) (7.6% of 721 randomly selected systems)a State of Maine Survey (1998) 125 public water supplies (16% of tested supplies)a,b California Monitoring Data (1999)d 48 sources (0.9% of sources)a a) Most of detections were <20 g/L b) All of detections were <35 g/L c) This study is incomplete and the number of community systems may change as data for 3 additional states are added d) Monitoring is continuing and the number of sources with MTBE may change

  13. Ground Water Issue 2 • Some community water supply • and domestic wells have had to • be removed from use or • treatment has been necessary.

  14. Community Water Supply Systems/Wells with MTBE > 20 mg/L • National level data are not available at this time • Examples of what we do know: • - OSTP (1997) • - Illinois 3 systems • - Texas 1 system • - 12 Eastern States Compilation (1999) a • -Virginia 3 systems • -Connecticut 2 systems • - Rhode island 1 system • - State of Maine Survey 0 wellsb • (1998) • - California Monitoring Data 5 systems • (1999) c a) This study is incomplete and the number of systems may change as data for 3 additional states are added b) exceeding 35 mg/L, State of Maine’s MCL c) Monitoring is continuing and the number of systems may change

  15. Contamination of Private Wells From MTBE Releases at LUST Sites (Source: University of Massachusetts survey, 1998 unpublished data) No private well contaminated or did not respond to survey 1-10 private wells contaminated 11-20 private wells contaminated 31-40 private wells contaminated >40 private wells contaminated Note: The results of this survey are discussed in an article by: Hitsig, R., 1998, Study Reports LUST programs are feeling the effect of MTBE releases, Soil and Ground Water Cleanup, August/September, p. 15 - 19.

  16. Ground Water Issue 3 • A variety of sources are • responsible for the occurrence of • MTBE in ground water.

  17. Possible Sources of MTBE in Ground Water Point Sources Non-point Sources refineries vehicle emissions pipelines vehicle evaporative losses storage tanks atmospheric deposition accidental spillage urban runoff homeowner disposal recreational watercraft emissions during fueling

  18. Hierarchy of MTBE Ground-Water Contamination Maximum level of MTBE Example Source in ground water • Point-source release > 100,000 g/L • (gasoline storage tank, • pipeline, etc.) • Recreational watercraft ~10 - 50 g/L • (emissions/losses) • Non-point sources ~1 - 10 g/L • (i.e. atmospheric deposition, • urban runoff, etc.)

  19. Ground Water Issue 4 • Active remediation of MTBE may • be required at some gasoline • release sites where MTBE has • migrated much further than • conventional gasoline • hydrocarbons.

  20. Field Experience Shows That MTBE Migrates Farther Than BTEX From Release Sites Examples: - Laurel Bay Marine Corps Station, Beaufort, South Carolina - Borden Canadian Air Force Base site - North Windam* and North Berwick*, Maine - Port Hueneme, California* - East Patchogue, New York* - rural Sampson County, North Carolina * migrated > 1000 ft

  21. Prepared by: K. Greene, Navy Facility Engineering Service Center (NFESC), 1998

  22. Summary of the Degradation Pathway of MTBE MTBE microbial conversion in ground water chemical conversion in the atmosphere tert-butyl formate tert-butyl alcohol tert-butyl alcohol acetone acetone carbon dioxide carbon dioxide (Adapted from: Church and others, 1997, Method for determination of methyl tert-butyl ether and its degradation products in water: Environmental Science and Technology, vol. 31, no. 12, pp. 3723-3726.)

  23. H C H H H H C C O H H C H H H Tert-Butyl Alcohol in Ground Water • Stability due to tertiary carbon • OSTP finding: “resistant to biodegradation” • No national occurrence data for ground water • Half-life of 8 weeks to 1 year in unacclimated ground-water systems • (Howard and others, 1991, Handbook of Environmental Degradation Rates: Lewis Publishers, Inc., Chelsea, MI, pp. 156-157) • High levels of TBA (up to 5,000 mg/L) are still present in ground water 12 years after UST gasoline release • (Landmeyer and others, 1998, Fate of MTBE Relative to Benzene in a Gasoline-Contaminated Aquifer (1993-98): Ground Water Monitoring and Remediation, Fall, pp. 93-102.) • (Note: TBA is believed to have been present in the gasoline released at this site)

  24. Other Ether and Alcohol Oxygenates • Ethers: • - tert-amyl methyl ether (TAME) • - ethyl tert-butyl ether (ETBE) • - diisopropyl ether (DIPE) • Alcohols: • - ethanol • - methanol • - tert-butyl alcohol (TBA)

  25. Infinitely soluble in water • Little sorption to aquifer material will occur • - ethanol transport same as water • velocity and MTBE • Readily biodegraded, except at very high levels (i.e. > 10%) • Low potential for long-range transport  Estimated Behavior and Fate of Ethanol in Ground Water (Note: based on physical and chemical properties and laboratory degradation knowledge)

  26. Estimated Behavior and Fate of TAME, DIPE, and ETBE in Ground Water (Note: based on physical and chemical properties and laboratory degradation knowledge) • Solubilities in water from RfG gasoline are somewhat lower than MTBE but never the less still high • Sorption to aquifer material and transport velocities in water will be similar to benzene • Rapid degradation is not expected, certainly slower than BTEX • All 3 compounds have the potential for long-range transport

  27. By-Products of Ethanol and TAME in Ground Water Ethanol* acetaldehyde formaldehyde acetic acid TAME tert-amyl alcohol methyl acetate acetone * (Source: Howard and others, 1990, Handbook of environmental fate and exposure data for organic chemicals, Volume II: Lewis Publishers, Chelsea, MI, 546p. )

  28. Additional Thoughts 1. What level of contamination of gasoline oxygenates in drinking water is acceptable? - A risk manager’s perspective vs. the publics’ perspective 2. How well do the Nation’s drinking-water programs (local, state, and federal) address chemical contaminants that are of concern primarily because of their taste and odor? - Few states have set acceptable drinking- water levels for oxygenates - Replacing drinking-water wells or treating contaminated water can be expensive

  29. Additional Thoughts (cont.) 3. What is the appropriate mix of oxygenate drinking-water monitoring versus well head protection versus education of local managers/planners? 4. What is the hydrogeology community’s perspective on the large-scale use of oxygenates in gasoline? - 1998 editorial in Ground Water, “MTBE--A long-term threat to ground water quality”, vol. 36, No. 5

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