““Ground-Water Issues Associated with the Use of Ground-Water Issues Associated with the Use of MTBE and Other Oxygenates in Gasoline”MTBE and Other Oxygenates in Gasoline”
Presented on January 22, 1999 to
Clean Air Act Advisory Committee Panel on Clean Air Act Advisory Committee Panel on Oxygenate Use in GasolineOxygenate Use in Gasoline
Prepared by
John Zogorski, David Bender, Mike Moran, and Mike HaldeJohn Zogorski, David Bender, Mike Moran, and Mike HaldeNational Water-Quality Assessment ProgramNational Water-Quality Assessment Program
U.S. Geological SurveyU.S. Geological SurveyRapid City, SD Rapid City, SD
(Note: This document contains some provisional water-quality information that may change pending final quality-assurance review)
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
SolubilityFrom (g/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)
Estimated Solubility of MTBE in Water Estimated Solubility of MTBE in Water at 55 Degrees Fahrenheitat 55 Degrees Fahrenheit
Note: USEPA advisory for drinking water is 20-40 g/La v/v -- volume MTBE per volume gasoline
MTBE Benzene Ethylbenzene
solid phase
dissolved phase
Assumptions:foc = 0.001
1 liter of aquifer = 2.0 kg sand + 0.25 kg water
Example of Partitioning of MTBE and 2 Gasoline Example of Partitioning of MTBE and 2 Gasoline Hydrocarbons Between the Aquifer Material and WaterHydrocarbons Between the Aquifer Material and Water
n = 0.25
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.
Example of Difference in Migration of Water, MTBE and Example of Difference in Migration of Water, MTBE and 2 Gasoline Hydrocarbons2 Gasoline Hydrocarbons
2.0
Elapsed time since
release
Travel distance (in miles)
0
3.3 years
WaterMTBEBenzeneEthylbenzene
10 years
30 years
foc = 0.001n = 0.25s = 2.65 g/cm3
vf = 1 ft/day
1.0 1.50.5 1.25
Assumptions:
no biodegradation
0.25 0.75 1.75
continuous point source
isotropic sand
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.
Biodegradation of MTBE in Ground WaterBiodegradation 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
C O CH
H
H
CH
H
HC HH
H
CH
HH
Flow Paths and Contributing Area to a Flow Paths and Contributing Area to a Community Water-Supply WellCommunity Water-Supply Well
Regional ground-water flow
5 year
Cross section
15 year10 year
20 year25 year
Plan view
Contributing area
Saturatedzone
UnsaturatedzoneRecharge
Recharge
30 year
Discharge
Discharging well
Isotropic sand
Median Ground-water ageMonitoring wells
screened near watertable
Monitoring wellsscreened at
moderate depth
Community water- supply wells screened
at bottom of aquifer
(N = 50)
(N = 30)
(N = 20)
MTBE Detection Frequency versus Median MTBE Detection Frequency versus Median Ground-Water Age for Glassboro, N.J. Study AreaGround-Water Age for Glassboro, N.J. Study Area
(Note: based on provisional USGS data)(Note: based on provisional USGS data)
Note: N = number of wells sampled.
Ground Water Issue 1Ground 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.
MTBE in Ambient Ground Water of U.S. NAWQA DataMTBE in Ambient Ground Water of U.S. NAWQA Data(2,743 wells, mix well types, mix of networks, 1993-98 data, 0.2 (2,743 wells, mix well types, mix of networks, 1993-98 data, 0.2 g/L RL)g/L RL)
(Note: based on provisional USGS data)(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
Detection of MTBE in Ambient Ground WaterDetection of MTBE in Ambient Ground Water(NAWQA data, 1993-98, 0.2 (NAWQA data, 1993-98, 0.2 g/L RL)g/L RL)(Note: based on provisional USGS data)(Note: based on provisional USGS data)
• MTBE Use21. % 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 controlledto assess the true effect of high MTBE use on detectionsin ambient ground water.
MTBE in Community Water Supply Wells of U.S.MTBE in Community Water Supply Wells of U.S.(Note: based on provisional USGS data)(Note: based on provisional USGS data)
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
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
Ground Water Issue 2Ground Water Issue 2
• Some community water supply
and domestic wells have had to
be removed from use or
treatment has been necessary.
Community Water Supply Systems/WellsCommunity Water Supply Systems/Wellswith MTBE with MTBE >> 20 20 g/Lg/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
addedb) exceeding 35 g/L, State of Maine’s MCLc) Monitoring is continuing and the number of systems may change
No private well contaminated or did not respond to survey1-10 private wells contaminated11-20 private wells contaminated31-40 private wells contaminated>40 private wells contaminated
Contamination of Private Wells From MTBE Releases at LUST Sites(Source: University of Massachusetts survey, 1998 unpublished data)(Source: University of Massachusetts survey, 1998 unpublished data)
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.
Ground Water Issue 3Ground Water Issue 3
• A variety of sources are
responsible for the occurrence of
MTBE in ground water.
Possible Sources of MTBE in Ground WaterPossible 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
Hierarchy of MTBE Ground-Water ContaminationHierarchy of MTBE Ground-Water Contamination
Maximum level of MTBEExample 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.)
Ground Water Issue 4Ground 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.
Field Experience Shows That MTBE Migrates Field Experience Shows That MTBE Migrates Farther Than BTEX From Release SitesFarther 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
Prepared by: K. Greene, Navy Facility Engineering Service Center (NFESC), 1998
MTBE
acetone
Summary of the Degradation Pathway of MTBESummary of the Degradation Pathway of MTBE
carbon dioxide
tert-butyl formate
microbialconversion
in ground water
tert-butyl alcohol
acetone
carbon dioxide
tert-butyl alcohol
chemicalconversion in the
atmosphere
(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.)
Tert-Butyl Alcohol in Ground WaterTert-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 g/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)
H
H
C O HCH
H
HC HH
C HH
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)
Estimated Behavior and Fate of Ethanolin Ground Water
(Note: based on physical and chemical properties and laboratory degradation knowledge)
• 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 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
By-Products of Ethanol and TAMEin Ground Water
TAME
tert-amyl alcoholmethyl acetate
acetone
Ethanol*
acetaldehydeformaldehyde
acetic acid
* (Source: Howard and others, 1990, Handbook of environmental fate and exposure data for organic chemicals, Volume II: Lewis Publishers, Chelsea, MI, 546p. )
Additional ThoughtsAdditional 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
Additional Thoughts (cont.)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