““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