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Mr. Chairman and subcommittee
members, I appreciate the opportunity to appear before the Subcommittee on
Environment and Hazardous Materials to testify on the findings of U.S.
Geological Survey (USGS) studies on water-quality issues related to methyl
tertiary-butyl ether, commonly referred to as MTBE.
As you may
know, the mission of the USGS is to assess the quantity and the quality of the
earth’s resources and to provide information that will assist resource
managers and policy makers at the Federal, State, and local levels in making
sound decisions. Assessment of
water-quality conditions and research on the fate and transport of pollutants in
water are important parts of the overall mission of the USGS.
USGS studies
over the past 8 years have shown that MTBE typically is present at very low
concentrations in shallow ground water within areas where MTBE is used.
Our studies also suggest that MTBE levels do not appear to be increasing
over time and are almost always below levels of concern from aesthetic and
public health standpoints. The few
locations in our database with high concentrations of MTBE may be associated
with leaking underground storage tanks.
Based on
comparisons with the U.S. Environmental Protection Agency’s (USEPA) drinking
water advisory, the health threat to water supplies is small compared to other
water-related issues. MTBE is
primarily an aesthetic (taste and odor) problem.
However, we believe it may be prudent to continue our monitoring and
research within available resources so that we can verify that the threat
remains low and to further the understanding of this chemical to contribute to
effective strategies to protect our Nation’s water supplies and to efficiently
remediate those ground waters that have become contaminated.
The results I
will present today come from about a decade of sampling and study of MTBE and
other Volatile Organic Compounds (VOCs). MTBE
is one of about 60 VOCs that we measure on a routine basis in our water-quality
studies.
The single
largest study we have made of MTBE is part of our National Water Quality
Assessment (NAWQA) Program. Based
on initial monitoring data for wells sampled in 1993-94 in the NAWQA Program, we
published a report on the occurrence of MTBE in shallow ground water in urban
and agricultural areas. At that
time our data set was fairly small—about 200 randomly selected wells in urban
areas and 500 randomly selected wells in agricultural areas.
We reported finding MTBE in about 25 percent of urban wells and 1 percent
of agricultural wells. Many of the
MTBE detections were low concentrations. In
fact, only 3 percent of the urban wells exceeded 20 micrograms per liter, the
lower limit of USEPA’s consumer advisory for taste and odor.
Also, many of the urban wells that contained MTBE were located in Denver,
Colorado, and in New England, both areas with extensive use of MTBE prior to our
sampling. At the time, MTBE was a
chemical for which usage had increased dramatically in recent years and we knew
it moved in the subsurface differently from other gasoline components.
Thus, even though it was detected in few wells and at very low levels, we
believed it would be prudent to continue studying it at many locations and over
a period of several years to learn more about its national distribution and
fate.
Since our first
report in 1995, we have sampled additional wells in the NAWQA Program.
This now gives us much better coverage of aquifers across the Nation.
For the period 1993-2000, we sampled 4,260 wells (or springs) for MTBE
and a wide range of other compounds. Of
this total, 396 are public water-supply wells; 1,847 are domestic wells; and
2,017 are monitoring wells (or other wells not used for drinking water). At a reporting level of 0.2 micrograms per liter (a level
that is one one-hundredth of the USEPA advisory level), we detected MTBE in 5.2
percent of the wells sampled. Most
of the MTBE detections are low concentrations.
None of the public water-supply wells and only one domestic well had MTBE
at a concentration above the lower limit of USEPA’s advisory.
Through our interpretations of this large data set we have also
determined that low-levels of MTBE are detected in about 1 out of 5 wells in
MTBE high-use areas. Although we do
not expect to see a great change in these results over time, we recognize that
there may be a delay in the detection of MTBE in some wells—particularly those
that are deeper and may be farther from the source of contamination.
MTBE is the second most frequently detected volatile organic compound
(VOC). Chloroform, a drinking-water disinfection by-product and a
commercial solvent, is the most frequently detected VOC.
Based on our
NAWQA findings and interests of other agencies, we have undertaken two allied,
large-scale studies to further our understanding of the occurrence of MTBE and
other VOCs. We have completed a
study in cooperation with the USEPA’s Office of Ground Water and Drinking
Water. For the period 1993-98, we
have compiled information on the occurrence of MTBE and other VOCs in drinking
water supplied by Community Water Systems in 12 States in the Northeast and
Mid-Atlantic Regions of the United States.
Parts of these Regions are designated Reformulated Gasoline (RFG) Areas
and, in general, these RFG Areas have used MTBE in gasoline in large amounts for
many years. USGS obtained the MTBE/VOC
data from each State’s drinking-water program.
We then randomly selected about 20 percent of the almost 11,000 Community
Water Systems in the study area for our analysis.
States with MTBE data included Connecticut, Maine, Maryland,
Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and
Virginia. Data for MTBE were not
available for Delaware and Pennsylvania, at the time the study was completed.
At a reporting
level of one microgram per liter, about 9 percent of the Community Water Systems
had detectable MTBE in their drinking water; however, most of the detections
were low concentrations. Ten
Community Water Systems had MTBE concentrations that equaled or exceeded the
lower limit of the USEPA advisory, or about 1 percent of all Community Water
Systems with MTBE data. We also
confirmed that MTBE was detected more frequently in RFG Areas than elsewhere in
the two Regions. Furthermore,
larger Community Water Systems located in urban centers had a larger incidence
of MTBE detections.
We are also
working with the Metropolitan Water District of Southern California, and the
Oregon Graduate Institute of Science and Technology, to complete a study of MTBE,
other ether gasoline oxygenates, and other VOCs in select reservoirs, rivers,
and wells that supply Community Water Systems.
This study was partly funded through the American Water Works Association
Research Foundation (AWWARF). We
are in the final year of this 4-year project.
For this study,
we tested the source water of 954 randomly selected Community Water Systems,
including 579 wells, 171 rivers, and 204 reservoirs.
Samples were collected in all 50 States and Puerto Rico, and varied sizes
of systems were included. All
sampling for this project is completed; however, some of our intended
interpretations and report writing are not yet completed and peer reviewed. Initial findings, which were reported on June 20, 2001, at
the Annual Conference of the American Water Works Association, were similar to
our findings noted earlier in this statement.
Specifically, when detected in source waters, the concentrations of MTBE
were almost always below the USEPA advisory.
However, MTBE was found in about 9 percent of all sources sampled (at a
reporting level of 0.2 micrograms per liter), and it was the second most
frequently detected VOC. A larger
detection frequency of MTBE was found in surface-water sources (14 percent),
than ground-water sources (5 percent). In
general, the detection of MTBE increased with increasing size of the Community
Water Systems. MTBE was detected in
about 4 percent of Community Water Systems serving less than 10,000 people, and
in nearly 15 percent of systems serving greater than 50,000 people.
Many of the surface-water sources sampled in the AWWARF study were large
rivers and reservoirs that had recreational watercraft usage.
Older models of watercraft motors are known to release a fraction of
non-combusted gasoline to water and this, in part, may explain the larger
occurrence of MTBE in surface-water sources.
We also conduct
research on the fate and transport of MTBE in ground water and surface water
through the USGS Toxic Substances Hydrology Program.
In this program, we explore the range of geochemical and microbiological
processes that determine how MTBE will behave when it enters soil, ground water
or surface water. This research is
demonstrating that MTBE does biodegrade under a wide range of environmental
settings although at slower rates than many of the components of traditionally
formulated gasoline. These ongoing
studies have important implications for predicting the future concentrations of
MTBE in water, where contamination has already occurred. These results are also
important for the design and selection of remediation plans.
As part of the
Toxic Substances Hydrology Program research, USGS scientists have demonstrated
that naturally occurring microorganisms can biodegrade MTBE in many hydrologic
environments, and in some cases, to harmless by-products.
In some situations, however, biodegradation may be incomplete and tert-butyl
alcohol (TBA) can be formed. Especially
noteworthy are the observations that MTBE biodegrades in ground water and soil
where sufficient oxygen is present and in bed sediments of streams, lakes,
wetlands, and estuaries where MTBE-contaminated ground water can ultimately
discharge. Essentially, these
environments can be considered to be natural sinks for MTBE removal.
As noted earlier, MTBE is expected to degrade slower in ground water than
gasoline hydrocarbons of traditional gasoline formations.
The length of time required to complete this removal is currently a topic
of ongoing investigation.
The USGS has
actively participated in two previous Federal reviews of MTBE and other
oxygenates in gasoline. A Blue
Ribbon Panel was appointed by the Administrator of the USEPA to investigate the
air-quality benefits and water-quality concerns associated with oxygenates in
gasoline, and to provide independent advice and recommendations on ways to
maintain air quality while protecting water quality.
In 1998-1999, Dr. John Zogorski of the USGS served as a water-quality
consultant to the Blue Ribbon Panel and three USGS scientists testified before
the Panel. An important finding of
the Blue Ribbon Panel is that the major source of MTBE ground-water
contamination appears to be releases from underground gasoline storage systems. Many of these tanks have been removed permanently or upgraded
in the 1990s, and thus this source is likely to diminish in the coming years.
Other major sources of water contamination were stated to be from small
and large gasoline spills and from recreational watercraft, especially those
with older model 2-cycle motors.
USGS has documented low levels of MTBE in urban air, urban precipitation,
and urban stormwater, and these sources may cause low concentrations of MTBE in
surface water and ground water. MTBE
has also been found in spills of home fuel oil in Northeastern States.
During 1995-96,
at the request of the USEPA and the Office of Science and Technology Policy (OSTP),
the USGS co-chaired an interagency panel to summarize what was known and unknown
about the water-quality implications of the production, distribution, storage,
and use of fuel. Our efforts were
published in 1997 as a chapter in a report entitled “Interagency Assessment of
Oxygenated Fuels” prepared by the National Science and Technology Council,
Committee on Environment and Natural Resources.
The chapter summarizes the scientific literature and data on the sources,
occurrences, concentrations, behavior, and the fate of fuel oxygenates in ground
water and surface water. We also
discussed the implications for drinking water and aquatic life, and made
recommendations of information needed to better characterize the occurrence of
MTBE and other oxygenates in the Nation’s drinking-water supplies.
Furthermore,
last year, USGS and Oregon Graduate Institute scientists co-authored a feature
article in the journal Environmental Science and Technology, a publication of
the American Chemical Society. A
salient part of the article summarized important information about MTBE
including: growth in production;
solubility, transport and degradation in ground water; releases from leaking
underground fuel tanks; and the effect of select factors, such as aquifer
recharge, the presence of low permeability stratum, and water utility pumping
rates. This information helped to
determine the likelihood of MTBE reaching community water-supply wells.
Based on available but admittedly incomplete data for 31 States, the
authors determined that about 9,000 community wells may have one or more leaking
underground storage tanks nearby (i.e., within 1-km radius of the well).
Because detailed information on the community wells, storage tanks, and
hydrogeology were not available, the authors could not determine the number of
wells at risk.
Unfortunately,
some of the press coverage of this article inaccurately stated that 9,000
drinking-water wells were contaminated with MTBE.
As stated in the journal publication, not all community wells with
gasoline releases nearby are at risk because not all gasoline releases contain
MTBE, and not all MTBE-gasoline releases are sufficiently large to pollute a
nearby well. Also, many wells draw
water from the deeper zones of aquifers and many wells are largely isolated from
land-surface contamination by low permeability stratum, technically called
aquitards. Based on these factors,
data from the studies mentioned previously, and a recent survey by others, we
would estimate that the number of community wells contaminated is far lower than
9,000 for 31 States.
In summary, the
USGS has not found widespread, high-level MTBE contamination in rivers,
reservoirs, and ground water that are actively used as the sources for Community
Water Systems. Furthermore, we have
not found such contamination in public wells and domestic wells sampled in our
NAWQA Program, or in the drinking water of Community Water Systems in 10
Northeastern and Mid-Atlantic States. We
have, however, identified MTBE (and some other VOCs) fairly frequently in ground
water, source water, and drinking water at concentrations below USEPA’s
advisory. We also conclude that the
frequency of detection of MTBE is larger in RFG Areas, in comparison to other
areas of the Nation. Approximately
85 million people reside in RFG areas that use MTBE extensively, and drinking
water in these areas is provided almost equally from surface water and ground
water.
There are
multiple strategies for dealing with situations where MTBE contamination of
ground water has taken place and these should include strategies that take
maximum advantage of the natural attenuation that we observe in our research. Within available resources, more research would be helpful to
provide guidance on the most cost-effective strategies for protecting drinking
water sources in those areas that have become contaminated.
I appreciate
the opportunity to testify on the results of USGS assessments and research on
MTBE. I am happy to try to respond
to any questions of the Subcommittee.
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