|
n • n
<br /> ri
<br /> 4
<br /> and to aquifer vulnerability To define nonpoint The degradation products of some organic chemicals
<br /> sources of MTBE contamination, information is can be toxic Questions related to the fate of MTBE
<br /> needed on the release of MTBE to the atmosphere include (1) What is the long-term fate of MTBE, and
<br /> from various activities MTBE can be released to the its degradation products, in ground water? (2) What is
<br /> atmosphere from a variety of sources including the half life of MTBE in ground water under aerobic
<br /> industrial stack and fugitive emissions, refueling at and anaerobic conditions in various aquifers? There
<br /> service stations, and mobile sources, such as also may be degradation products of MTBE in the air,
<br /> automobiles With the possible exception of industrial such as tert-butyl formate (Japan and others, 1991),
<br /> emissions, the amount of MTBE released to the urban which enter shallow ground water with recharge
<br /> atmosphere from these other sources is not well water Investigation of these degradation products is
<br /> documented Once MTBE is in the atmosphere, some
<br /> cnecessary to a full understanding of the fate of MTBE
<br /> an be returned with precipitation, but more research
<br /> is needed to determine the concentrations of MTBE in
<br /> precipitation and in surface runoff on a seasonal basis In order to determine if MTBE concentrations are
<br /> likely to rise above current levels and potentially rise
<br /> A better understanding of the transport of MTBE to levels that pose a health threat, it is necessary to
<br /> from land surface to shallow ground water, and from understand three things about the compound (1) the
<br /> shallow to deeper aquifers would be used to protect pathways by which it enters the ground water, (2) the
<br /> public water supplies and in developing wellhead processes by which it is transported in ground water,
<br /> protection plans for public water supplies Questions and (3)the rates at which it degrades Only when all
<br /> related to the transport of MTBE include (1) Can three of these issues are reasonably well understood
<br /> MTBE in precipitation or stormwater runoff recharge can meaningful projections be made of the potential
<br /> the shallow ground water, if so,under what conditions for MTBE reaching dangerous levels over long
<br /> and in what concentrations? (2) How quickly, and at periods of use The U S Geological Survey is
<br /> what concentrations, can MTBE be transported from beginning to conduct research on aspects of all of
<br /> shallow to deeper ground water? (3) What is the these processes and is in close communication with
<br /> maximum extent of a MTBE plume originating from a other scientists studying these questions In addition,
<br /> • point source relative to the BTEX compounds? Depth the NAWQA program will continue to monitor some
<br /> to water, recharge rates, permeability of the wells in all Study Units, providing a continuing
<br /> unsaturated zone, and other hydrogeologic character- empirical check on the changes in levels of MTBE in
<br /> istics are likely to affect the transport of MTBE ground water The U S Geological Survey will
<br /> through the unsaturated zone Because MTBE is continue to report to the public, regulatory agencies,
<br /> mobile and persistent in ground water,it is reasonable industry, and the scientific commuruty on the results
<br /> to expect that it will move from shallow to deep of its research and monitoring on this emerging water-
<br /> ground water with time, but it is not known how quality issue
<br /> quickly and at what concentrations Knowledge on the
<br /> maximum extent of a MTBE plume relative to BTEX
<br /> compounds originating from a single gasoline contam-
<br /> ination source will help determine if point-source REFERENCES CITED
<br /> contamination is responsible for the widespread
<br /> detection of small concentrations of MTBE in the Ainsworth, S , 1992, Oxygenates seen as hot market by
<br /> absence of BTEX compounds industry Chemical Engineering News,v 70,p 26-30
<br /> Additional study and data on the fate of MTBE are Allen,M and Grande, D, 1995, Reformulated gasoline air
<br /> needed to determine if MTBE, or its degradation monitoring study Madison,Wisconsin Department of
<br /> products, will accumulate in ground water over time Natural Resources,AM-175-95,24 p
<br /> The accumulation of MTBE in ground water may not
<br /> necessarily result in an increase in concentrations with Anderson, H A, Hanrahan, Lawrence, Goldring, Jay, and
<br /> tune, but its detection would become more frequent Dewey,Bryan, 1995,An investigation of health con-
<br /> The degradation of some orgaruc chemicals in cerns attributed to reformulated gasohne use in south-
<br /> aquifers can be very slow, with a half life of decades eastern Wisconsin Madison, Wisconsin Department
<br /> . or longer, to breakdown to carbon dioxide and water of Health and Social Services,99 p
<br /> References Cited 13
<br />
|