Methyl Tertiary Butyl Ether (MTBE)

MTBE is used primarily as an oxygenate in gasoline fuels to increase their octane rating. The Clean Air Act mandated the use of oxygenates (although not MTBE specifically) in nine metropolitan areas that have severe ozone pollution. The use of MTBE as an anti-knock, octane rating boosting compound began in 1979 to replace tetra ethyl lead, which was being phased out (API 2000). The 1990 Clean Air Act Amendments established two new fuel programs administered by U.S. EPA that required the use of "federal oxygenated gasoline" or "federal reformulated gasoline." (API 2000). These programs greatly expanded the use of oxygenates nationwide. In 2005, Congress passed the Energy Policy Act, which removed the oxygenate requirement for reformulated gasoline (RFG). At the same time, Congress also instituted a renewable fuel standard. In response, refiners made a wholesale switch, removing MTBE and blending fuel with ethanol. According to EPA's RFG Survey Data, MTBE has not been used in significant quantities in RFG areas since 2005. A similar decrease in MTBE use has also been observed in conventional gasoline areas (EPA 2013).

In surveys conducted by the U.S. Geological Survey (USGS) from 1993 to 2002 (Moran et al. 2004), the overall detection frequency of MTBE was similar to the detection frequencies of other VOCs that have much longer production and use histories in the United States. The detection frequency of MTBE was higher in drinking water and lower in source water and groundwater. The overall detection frequency of MTBE relative to other widely used VOCs indicates that MTBE is an important concern with respect to groundwater management. Moran et al. found that the probability of detecting MTBE was strongly associated with population density, use of MTBE in gasoline, and high groundwater recharge, and was only weakly associated with density of leaking underground storage tanks, soil permeability, and aquifer consolidation. Groundwater from public-supply wells and shallow groundwater underlying urban land-use areas has a greater probability of MTBE contamination compared to groundwater from domestic wells and groundwater underlying rural land-use areas.

According to the Toxics Release Inventory for 2012, 237,732 lbs. of MTBE were released to the air, 2,083 to surface waters, and 1,550,558 to landfills; 17,907 lbs. were disposed of in underground injection wells; and 93,472 lbs. were transferred from the user to off-site disposal. The reporting requirements are only for specific industry categories where the entity manufactures or processes more than 25,000 lbs. of a TRI-listed chemical or otherwise uses more than 10,000 lbs. of a listed chemical in a given year. Retail gasoline stations would not be covered.

2006 Survey of State Experiences with Petroleum and Hazardous Substance Releases at LUST Sites, Heating Oil Tanks, and Out of Service Tanks
New England Interstate Water Pollution Control Commission (NEIWPCC), 2006

In 2006, NEIWPCC performed a survey of all 50 states that asked, among other questions, about oxidant occurrence, cleanup standards, and methods used to test for oxidants.

• Survey Results Summary Attachment
• State Standards Attachment

An Evaluation of MTBE Impacts to California Groundwater Resources
Anne M. Happel, Edwin H. Beckenbach, Rolf U. Halden.
UCRL-AR-130897, 80 pp, 1998.

Identifying the Usage Patterns of Methyl tert-Butyl Ether (MTBE) and Other Oxygenates in Gasoline Using Gasoline Surveys
M. Moran, R. Clawges, and J. Zogorski.
American Chemical Society 219th Meeting, San Francisco, Calif., 26-31 March 2000. Preprints of Papers, Vol 40 No 1, p 209-213, 2000.
Contact: Michael Moran, mjmoran@usgs.gov

Impacts of MTBE on California Groundwater
G.E. Fogg, M.E. Meays, J.C. Trask, C.T. Green, E.M. LaBolle, T.W. Shenk, and D.E. Rolston.
Health and Environmental Assessment of MTBE: Report to the Governor and Legislature of the State of California as Sponsored by SB 521. Vol 4: Ground and Surface Water, 101 pp, 1998

This assessment report addresses the impacts of MTBE to the state's groundwater used for drinking as well as risks to the state's groundwater resources associated with MTBE leaks.

Interagency Assessment of Oxygenated Fuels
Office of the President, Office of Science and Technology Policy, 264 pp, 1997.

Life Cycle of Methyl tert-Butyl Ether in California Public Water Supply Wells
McHugh, T.E., S.R. Rauch, S.M. Paquette, J.A. Connor, and A.D. Daus.
Environmental Science & Technology Letters 2(1):7-11(2015)

The California Department of Public Health Water Quality Analyses database provided data used to evaluate the extent of MTBE in public water supply wells in California and how these impacts have changed over time. The data show that MTBE has never been detected in >98% of 13,183 public water supply wells tested for MTBE. The number of wells with first-time detections of MTBE peaked in 2000 and has decreased by 80% since that time. For the 188 wells in which MTBE has been detected at least once, MTBE was not detected in the most recent analysis of 142 of these wells. These results indicate that the impact of MTBE on public water supply wells in California has peaked and is declining.

Methyl tert-butyl Ether Occurrence and Related Factors in Public and Private Wells in Southeast New Hampshire
J.D. Ayotte, D.M. Argue, and F.J. McGarry.
Environmental Science & Technology 39(1):9-16(2005)
U.S. Government Printing Office, Serial No. 107-108, 82 pp, 2002.

MTBE Contamination in Groundwater: Identifying and Addressing the Problem
Hearing Before the Subcommittee on Environment and Hazardous Materials of the Committee on Energy and Commerce, House of Representatives, One Hundred Seventh Congress, Second Session.
U.S. Government Printing Office, Serial No. 107-108, 82 pp, 2002.

Expert testimony to inform the Committee how many parts of our country are facing MTBE contamination in the ground water and drinking water; how severe the contamination is and a response time frame protective of human health; how MTBE gets into ground water supplies; extent of current local, state, and federal efforts to protect water supplies; and efforts needed to ensure the safety of the environment against MTBE contamination.

MTBE and Other Volatile Organic Compounds—New Findings and Implications on the Quality of Source Waters Used for Drinking-Water Supplies
U.S. Geological Survey Fact Sheet, FS-101-01, 2 pp, 2001.
Contact: John Zogorski, jszogors@usgs.gov

A National Survey of Methyl tert-Butyl Ether and Other Volatile Organic Compounds in Drinking-Water Sources: Results of the Random Survey
Stephen J. Grady.
U.S. Geological Survey Water-Resources Investigations Report 02-4079, 94 pp, 2003.
Contact: Stephen J. Grady, sgrady@usgs.gov

Occurrence and Distribution of Methyl tert-Butyl Ether and Other Volatile Organic Compounds in Drinking Water in the Northeast and Mid-Atlantic Regions of the United States, 1993-98
S. Grady and G. Casey.
U.S. Geological Survey, Water-Resources Investigations Report 00-4228, 131 pp, 2001.
Contact: Stephen J. Grady, sgrady@usgs.gov

Occurrence of Methyl Tertiary-Butyl Ether (MTBE) in Groundwater at Leaking Underground Storage Tank Sites in Washington
Washington State Department of Ecology, Publication No. 00-09-054, 23 pp, 2000

Occurrence of MTBE and VOCS in Drinking Water Sources of the United States: Executive Summary
B. Koch, M. Dale, J. Zogorski, G. Delzer, S. Grady, T. Ivahnenko, R. Clawges, and P. Tratnyek.
IWA Pub., London. AwwaRF Report 90954F, 2003

Occurrence and Implications of Methyl tert-Butyl Ether and Gasoline Hydrocarbons in Ground Water and Source Water in the United States and in Drinking Water in 12 Northeast and Mid-Atlantic States, 1993-2002
M.J. Moran, J.S. Zogorski, and P.J. Squillace.
U.S. Geological Survey Water-Resources Investigations Report WRIR 03-4200, 32 pp, 2004.
Contact: M.J. Moran, mjmoran@usgs.gov

Occurrence and Temporal Variability of Methyl tert-Butyl Ether (MTBE) and Other Volatile Organic Compounds in Select Sources of Drinking Water: Results of the Focused Survey
G. Delzer and T. Ivahnenko.
U. S. Geological Survey Water-Resources Investigations Report 02-4084, 72 pp, 2002.
Contact: Gregory Delzer, gcdelzer@usgs.gov

A Preliminary Assessment of the Occurrence and Possible Sources of MtBE in Ground Water of the United States, 1993-94
P. Squillace, J. Zogorski, W. Wilber, and C. Price.
U.S. Geological Survey Open-File Report 95-456, 1995.
Contact: Paul Squillace, pjsquill@usgs.gov

The Quality of Our Nation's Waters: Volatile Organic Compounds in the Nation's Ground Water and Drinking-Water Supply Wells
J.S. Zogorski, J.M. Carter, T. Ivahnenko, W.W. Lapham, M.J. Moran, B.L. Rowe, P.J. Squillace, and P.L. Toccalino.
U.S. Geological Survey Circular 1292, 112 pp, 2006.

Relations Between the Detection of Methyl tert-Butyl Ether (MTBE) in Surface and Ground Water and Its Content in Gasoline
M. Moran, M. Halde, R. Clawges and J. Zogorski.
American Chemical Society 219th Meeting, San Franciso, Calif., 26-30 March 2000. Preprints of Papers, Vol 40 No 1, p 195, 2000.
Contact: Michael Moran, mjmoran@usgs.gov

State Investigation Reports on MTBE
U.S. EPA, Office of Solid Waste, Underground Storage Tanks Program web page.

Strategies for Characterizing Subsurface Releases of Gasoline Containing MTBE
American Petroleum Institute (API) Publication 4699, 116 pp, 2000.

API Publication 4699 includes a review of the chemical properties and subsurface behavior of MTBE and other oxygenated fuel additives. It also provides an overview of characterization and monitoring issues at oxygenate release sites, as well as a detailed review of the tools and techniques used for subsurface assessment. The expedited site assessment process and the use of modern direct-push tools are particularly emphasized.

Water Quality Impacts of MTBE: an Update since the Release of the UC Report
Malcolm Pirnie, Oakland, CA.
Methanol Institute, Washington, DC. 16 pp, 2001.
Contact: The Methanol Institute, MI@methanol.org

A report prepared for the Methanol Institute challenges assumptions used in the 1998 report, "Health and Environmental Assessment of MTBE: Report to the Governor and Legislature of the State of California as Sponsored by SB 521," regarding the potential for widespread contamination of water supplies by MTBE.