United States
                           Environmental Protection
                          Office Of Solid Waste And
                          Emergency Response
  EPA 510-F-97-014
     January 1998
                           Office Of Underground Storage Tanks
Fact Sheet  #1
                           What Is MTBE?

                           Methyl tertiary-butyl ether (MTBE) is
                           a fuel additive made by combining
                           methanol and isobutylene. The meth-
                           anol is typically derived from natural gas;
                           isobutylene can be derived as a byproduct
                           of the petroleum refinery process. Since
                           1979, MTBE has been used in the United
                           States as an octane-enhancing
                           replacement for lead, pri-marily in mid-
                           and high-grade gasoline at concentrations
                           as high as 8 percent (by volume).  Since
                           the middle of the 1980s, it has been
                           widely used through-out the country for
                           this purpose. It is also used as a fuel
                           oxygenate at higher concentrations (11 to
                           15 percent by volume) as part of the U.S.
                           EPA's programs to reduce ozone and
                           carbon monoxide levels in the most
                           polluted areas of the country.

                           MTBE And  EPA's Clean
                           Air Program

                           The Oxygenated Fuel (Oxyfuel) and
                           Reformulated Gasoline (RFG) Programs
                           were initiated by the U.S. EPA in 1992
                           and 1995, respectively,
                           to meet requirements of the 1990
                           Clean Air Act Amendments (CAAA).
                                 The Oxyfuel Program

                                 The Oxyfuel Program requires 2.7-
                                 percent oxygen (by weight) in gasoline
                                 during fall and winter months to reduce
                                 carbon monoxide emissions. In order to
                                 meet this requirement, gasoline pro-
                                 ducers must use oxygen containing
                                 compounds termed "fuel oxygenates"
                                 (e.g., ethanol, MTBE). When MTBE is
                                 used to meet the Oxyfuel requirements, it
                                 is added at a concentration of approx-
                                 imately 15 percent (by volume) to

                                 Although the total number of areas par-
                                 ticipating in the Oxyfuel Program may
                                 change from year to year, as of Novem-
                                 ber 1997, the CAAA required 28 areas to
                                 participate. Some of these areas also use
                                 RFG in the non-winter months. The
                                 Minneapolis-St. Paul area is the only area
                                 to use Oxyfuel year round. The areas of
                                 the country that use Oxy-fuel are
                                 presented in Exhibit 1.

                                 The RFG Program

                                 The RFG Program requires 2-percent
                                 oxygen (by weight) year round in the
                                 most polluted metropolitan areas to re-
                                 duce ozone and smog. When MTBE is
                                 used to meet the RFG requirements, its
                                 concentration in gasoline is 11 percent
                                 (by volume).
        January 1998
                                1    MTBE Fact Sheet #1: Overview

                      Ten metropolitan areas are required by
                      the CAAA to use RFG (Baltimore,
                      Chicago, Hartford, Houston, Los
                      Angeles, Milwaukee, New York,
                      Philadelphia, Sacramento, San Diego).
                      Another 22 areas in 13 states and the
                      District of Columbia voluntarily par-
                      ticipate in the RFG Program (Arizona,
                      Connecticut, Delaware, Kentucky, Maine,
                      Maryland, Massachusetts, New
                      Hampshire, New Jersey, New York,
                      Rhode Island, Texas, and Virginia).
                      California has a separate statewide
                      program with more stringent standards
                      than the federal RFG program. As with
                      the Oxyfuel Program, the total number of
                      areas participating in the RFG Program
                      may change from year
                      to year. The areas of the country that use
                      RFG are shown in Exhibit 2.

                      Although more data need to be collected
                      to determine the specific benefits that
                      these programs have had on air quality,
                      the initial research has shown significant
                      reductions in carbon monoxide, ozone,
                      benzene, and other toxic air pollutants as
                      a result of the use of oxygenated fuels.

                      Why Is There Concern
                      About MTBE?

                      CERCLA ("Superfund") lists MTBE as
                      a hazardous substance. Although it is
                      known to be less toxic than many other
                      gasoline constituents, people have raised
                      concerns about the potential for acute
                      effects from inhaling it at service stations
                      and longer term effects from drinking
                      water contaminated with it. MTBE is
                      also considered a potential human

                      In comparison to petroleum products,
                      MTBE poses additional problems when it
                      escapes into the environment through
                      gasoline releases; typically from under-
ground storage tank systems, above-
ground storage facilities, or pipelines.
MTBE is capable of traveling through
soil rapidly, is much more soluble in
water than most other petroleum consti-
tuents, and is more resistant to bio-
degradation. As a result, it often travels
farther than other gasoline constituents,
making it more likely to impact public
and private drinking water wells. Be-
cause of its affinity for water and, con-
sequently, its tendency to form large
plumes, petroleum releases with MTBE
can be more difficult and costly to
remediate than petroleum releases that do
not contain MTBE.

U.S. EPA Health  Advisory

In December 1997, the U.S. EPA Office
of Water released Drinking Water
Advisory:  Consumer Accepta-bility
Advice and Health Effects Analysis on
Methyl tertiary-Butyl Ether (MTBE)
EPA 822-F-97-008. The document is a
summary and interpre-tation of the  latest
data on MTBE health effects and
organoleptic properties. It does not
impose any regulatory require-ments on
the providers of public drinking water;
instead, it recommends contaminant level
concentrations that would be acceptable
to most consumers  of public drinking
water supplies.

The recommendations are based
primarily on taste and odor thresholds.
The Advisory states that drinking water
containing ". . . concentrations in the
range of 20 to 40 //g/L [ppb] would
likely avoid unpleasant taste and odor
effects .. ." for a large majority of
people. The document also notes that
there is a large variation in the
concentrations people are able to detect.
The various factors influencing detection
limits include individual sensitivities,
MTBE Fact Sheet #1:  Overview
                       January 1998

                      water quality, and water temperature.  As
                      a result, some people may detect MTBE
                      below 20 ppb while others may not
                      notice it until levels exceed  100 ppb or

                      The document also concludes that there is
                      little likelihood that MTBE concen-
                      trations between 20 and 40 ppb would
                      cause adverse health effects because the
                      concentration is 4 to 5 orders of magni-
                      tude lower than the lowest concentra-tion
                      that caused observable health effects in
                      animals. Specifically, con-centrations in
                      this range are about 20,000 to 100,000 or
                      more times lower than the range of
                      exposure levels in which cancer or
                      noncancer effects were observed in
                      rodent tests.  This margin of exposure is
                      in the range of margins of exposure
                      typically provided for cancer effects in
                      drinking water standards and is greater
                      than such stan-dards typically provided
                      for noncancer effects.
After a thorough evaluation of all avail-
able health effect studies, the U.S. EPA
has determined that a lifetime exposure
health effects-based recommendation for
MTBE cannot be extrapolated from the
data at this time. Once additional studies
are completed that permit a justifiable
extrapolation for human exposure, the
current document will be replaced by a
final health advisory.

State Standards

Twenty-three states have established
regulatory guidelines  or standards for
MTBE contamination in groundwater or
drinking water.  These states are:
Arizona, Arkansas, California, Con-
necticut, Florida, Illinois, Indiana,
Kansas, Maine,  Maryland, Massachu-
setts, Michigan, New  Hampshire, New
Jersey, New Mexico, New York, North
Carolina, Pennsylvania, Rhode Island,
South Carolina, Vermont, Wisconsin, and
Wyoming.  Cleanup levels range from 12
ppb in Wisconsin to 240 ppb in
Michigan; three states (Arkansas,
Indiana, and Maryland) have site-specific
January 1998
    MTBE Fact Sheet #1:  Overview

MTBE Fact Sheet #1:  Overview
January 1998

January 1998
MTBE Fact Sheet #1:  Overview