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Session 1:
Oxygenates & Water Quality (continued)
Methyl-tert
Butyl Ether (MTBE) in Lakes and Ground Water at Lakeside
Communities, Northwestern New Jersey
Arthur L. Baehr, US
Geological Survey, West Trenton, NJ
Localized Recharge Influences on MTBE Transport and
Well Placement Considerations
Jim Weaver, US EPA,
Athens, GA
Environmental
Fate and Transport of Alternative Gasoline Oxygenates
Rula A. Deeb,
Malcolm Pirnie, Inc., Oakland, CA
Subsurface
Fate of Ethanol as a Gasoline Oxygenate
Susan E. Powers,
Clarkson University, Potsdam, NY
Dissolution Characteristics of Oxygenates from NAPL
Sources and the Impact on BTEX Groundwater Concentrations
Bill Rixey,
University of Houston, Calhoun, TX
Environmental
Implications of Ethanol and Alkylates in Gasoline after an
MTBE Phaseout: Results of a California Workshop
David Layton,
Lawrence Livermore National Laboratory, Livermore, CA
Oxygenate
Regulatory and Legislative Issues: How Will They Influence
Research Needs?
Bruce Bauman, API,
Washington DC
Methyl-tert Butyl Ether (MTBE) in Lakes and Ground Water
at Lakeside Communities, Northwestern New Jersey
Timothy J. Reilly
and Arthur L. Baehr, U.S. Geological Survey
Concentrations of
methyl-tert butyl ether (MTBE) in samples of water from
Cranberry Lake and Lake Lackawanna in northwestern New Jersey
ranged from 20 to 30 m g/L (micrograms per liter) and 5 to 14 m
g/L, respectively, during the summers of 1998 and 1999. MTBE
concentrations in samples from the upper 20 ft (feet) of Lake
Hopatcong during summer 1999 were about 10 m g/L. Concentrations
in samples from deeper (20–40 ft) parts of the lake were about
2 to 3 m g/L. The source of the MTBE in the lakes was
gasoline-powered watercraft. Other constituents of gasoline --tert-amyl
methyl ether (TAME) and benzene, toluene, ethyl benzene, and
xylenes (BTEX)-- were detected in the lakes, but at much lower
concentrations than MTBE. MTBE also was detected in samples from
13 of the 14 wells sampled near Cranberry Lake in fall 1998 and
summer 1999. The wells were selected to monitor ambient
ground-water quality and had no history of contamination. In
ground-water samples collected during fall 1998, MTBE
concentrations ranged from 0.12 to 19.8 m g/L, with a median of
0.43 m g/L. In samples collected during summer 1999, MTBE
concentrations ranged from 0.14 to 13.2 m g/L, with a median of
0.38 m g/L. MTBE was detected in samples from four of the five
wells near Lake Lackawanna in summer 1999; concentrations ranged
from 0.05 to 0.19 m g/L. Lake/well interaction is a feasible
explanation for the nearly ubiquitous presence of MTBE in ground
water near these lakes. The movement of water from lakes to
wells is physically possible because many static water levels
and nearly all pumped water levels in the wells were below the
water levels in the lakes.
Localized
Recharge Influences on MTBE Transport and Well Placement
Considerations
James W. Weaver, United States Environmental Protection
Agency
Vertical characterization of a gasoline release site at
East Patchogue, New York showed that methyl tert-butyl
ether (MTBE) and aromatic plumes "dived" as they
passed beneath a sand pit. That this behavior was caused
by aquifer recharge was shown by two pieces of evidence.
First by conducting a detailed investigation of hydraulic
conductivity variation in wells on either side of the sand
pit it was shown that no preferential flow paths exist.
Second, by modeling flow in the aquifer, the pattern of
recharge in the aquifer was shown to be sufficient to
cause the observed vertical migration of the plumes. The
model, available as a calculator on the EPA web site ( is
based on an analytical solution of the flow equation and
the theory of three-dimensional streamlines in Dupuit
flow. As further confirmation, the model has been shown to
reproduce observed plume diving patterns at similar sites
on Long Island. These sites provide confirmation of the
concepts and the ability to develop models to reproduce
field behavior. From this work cost-effective approaches
for site characterization could be developed that include
model forecasts of plume diving to determine well screen
placement. For design of sampling networks additional
capabilities must be included in the model, because of
unusual features of the Long Island sites: established,
well-characterized plumes and unique hydrogeologic
characteristics. For sites without existing data there is
a need to expand the model to include contaminant
transport. By using the estimated release date and
transport time to the recharge zones it can be determined
if a plume is likely to be affected by the feature. This
capability has been added to the calculator and compared
against data from the East Patchogue site. Further work is
underway on building more flexibility into the flow model.
Environmental
Fate and Transport of Alternative Gasoline Oxygenates
Rula A. Deeb, Ph.D. and Michael C. Kavanaugh, Ph.D.,
P.E., Malcolm Pirnie, Inc.
Oxygenates are added to gasoline in order to reduce
carbon monoxide emissions from non-stationary sources
thereby meeting the requirements of the 1990 Clean Air
Amendments and the Oxyfuel program. The most widely used
oxygenate is methyl tert-butyl ether (MTBE) with an
annual consumption of more than four billion gallons in
the United States alone. Less widely used oxygenates which
are approved by the US Environmental Protection Agency
(EPA) include ethanol, ethyl tert-butyl ether (ETBE),
tert-butyl alcohol (TBA), tert-amyl methyl
ether (TAME) and diisopropyl ether (DIPE). In this paper,
key physical and chemical properties of the
above-mentioned oxygenates will be used to elucidate their
fate and transport in the environment. When such data is
not readily available, estimation tools will be used to
approximate such properties. Using property information,
several first-order modeling analyses will be utilized to
illustrate the comparative differences between the
behavior of the various oxygenates following accidental
environmental releases of oxygenate-blended gasoline. One
modeling exercise will entail the development of a single
release scenario into two different hydrogeologic
subsurface environments with the first involving a sandy,
homogenous aquifer with rapidly moving groundwater (i.e.,
> 1 ft/day), and the second involving a loamy geology
with slower groundwater flow and a high organic carbon
content. The second exercise will entail modeling
oxygenate fate in surface water following gasoline
releases from recreational watercraft. The relative
biodegradability of the oxygenates will be estimated based
on laboratory, field or comparative raw data while taking
into account the molecular structure of each oxygenate as
well as the enzymatic pathways employed by microorganisms
for oxygenate biodegradation. Finally, a series of graphs
and tables will be presented to illustrate the differences
in the fate and transport of the various oxygenates in the
environment.
Subsurface
Fate of Ethanol as a Gasoline Oxygenate
Susan E. Powers, Clarkson University
The environmental fate of oxygenated gasoline has been
a significant concern since the discovery of widespread
MTBE contamination in groundwater and surface water. This
has lead to the phase out of MTBE use in many states and
the passage of a U.S. Senate resolution expressing support
for a nationwide phase-out of MTBE. Ethanol is currently
considered a suitable replacement. Problems associated
with past use of reformulated gasoline and the need for a
sound basis for future policies set the stage for the
research presented here, which is intended to increase our
understanding of the fate of ethanol in the subsurface due
to its use in gasoline. Gasoline with up to 10% ethanol
could leak at a slow rate from an underground storage tank
or more rapidly from an accident involving a tanker truck.
Larger spills of denatured ethanol from bulk terminals
into petroleum-contaminated soils can also occur. Ethanol
itself is very biodegradable, so is not expected to
migrate far from a spill site. However, the presence of
ethanol in the subsurface can affect the migration of
other more hazardous chemicals. Several transport and fate
processes could be affected by the presence of ethanol.
These include: 1) increasing the effective solubility of
BTEX and other gasoline compounds, 2) depleting electron
acceptors necessary for biodegradation of other gasoline
contaminants, thereby reducing the potential for natural
attenuation, and 3) altering the bulk fluid properties of
gasoline allowing the gasoline pool to spread further in
the presence of ethanol. Research results will be
highlighted that quantify the impact of these changes on
the migration of BTEX compounds within a plume of
contaminated groundwater. The uncertainties in the
research conducted to date will also be identified.
Dissolution
Characteristics of Oxygenates from NAPL Sources and the
Impact on BTX Groundwater Concentrations
William G. Rixey and Xiaohong He, University of Houston
In contrast to the issue of contamination by the oxygenate
itself, the potential for enhancing the concentrations of
benzene and other aromatic compounds in groundwater,
sometimes referred to as the cosolubility effect, has been
the subject of considerable speculation. A first step in
assessing this impact is to look at the equilibrium
partitioning of these compounds between an oxygenated fuel
and an aqueous phase. There have been several studies that
have focused on the equilibrium partitioning of systems
containing various oxygenates. From these studies it can
be concluded that for fuels containing ethers such as MTBE
there will be an insignificant enhancement in BTX
concentrations. Recent batch partitioning and column
experiments that characterize the dissolution of MTBE from
residually trapped gasoline will be presented that confirm
this conclusion. However, for fuels containing alcohols
such as ethanol, benzene concentrations in groundwater
near a NAPL source may increase depending upon the amount
of alcohol in the NAPL and the way in which the NAPL
contacts groundwater. The results of experiments that
assess the impact of ethanol, specifically how a source of
contaminated groundwater is generated and how the
concentrations of benzene and other aromatic hydrocarbons
in groundwater are impacted, will also be presented. These
experiments include 1) one-dimensional laboratory column
studies to quantitatively simulate both the (i) generation
of the source and (ii) the subsequent transport downstream
of the source; and 2) laboratory studies to visualize the
process of source generation. The implications of the
results of these experiments on the potential enhancement
in BTX source concentrations and on the longevity of
source concentrations of ethanol for gasoline releases
will be discussed.
Environmental
Implications of Ethanol and Alkylates in Gasoline after an
MtBE Phase Out: Results of a California Workshop
David W. Layton and David W. Rice, Lawrence Livermore
National Laboratory
In March 1999, the Governor of California issued an
executive order requiring that MtBE be phased out of
gasoline by Dec. 31, 2002. The phase out was prompted by
concerns that MtBE poses a significant threat to the State’s
surface waters and groundwaters. The only oxygenate that
is certified by California to replace MtBE is ethanol, but
to accommodate the increased use of ethanol in gasoline
other modifications to the base gasoline will have to be
made. For example, ethanol contains nearly twice as much
oxygen as MtBE and so less is required to meet the fuel
oxygen requirement of 2 wt%. As a consequence, other
high-octane hydrocarbons such as alkylates (branched
alkanes) must be added to compensate for the lost volume.
In addition, ethanol increases the Reid vapor pressure of
gasoline, and to meet vapor pressure limits for the
ozone-forming season, other high-vapor pressure components
such as pentanes will have to be removed. If California is
granted a waiver from the oxygenate requirement of the
Clean Air Act, refiners will have greater flexibility in
formulating gasolines that satisfy regulations established
by the California Air Resources Board. To address
potential environmental issues concerning the increased
use of ethanol and alkylates in gasoline, the U.S.
Department of Energy sponsored a workshop in Oakland,
California, April 10-11, 2001, that covered a broad range
of topics of interest to the regulatory and research
communities as well as fuel companies. The purpose of this
paper is to provide a summary of the important issues
raised at the workshop and to provide an update of on
going research involving the phase out of MtBE. Work
performed under the auspices of the U.S. Department of
Energy by the University of California, Lawrence Livermore
National Laboratory under contract No. W-7405-Eng-48.
Oxygenate
Regulatory and Legislative Issues: How Will They Influence
Research Needs?
Bruce Bauman, American Petroleum Institute
During the last 6 years, concerns regarding the impacts
of gasoline oxygenates on surface and ground water quality
have been the subject of considerable deliberation in
local, state and national government bodies, including the
legal system. Despite the high profile of this issue,
there do not appear to be any near-term Solomonic
decisions that will resolve the health, environmental and
gasoline supply issues that have been at the center of
debate. Several states have enacted bans of MTBE that will
take effect in the next 18-30 months, and states are
continuing to review their current corrective action
guidelines to address oxygenates. Congress is evaluating
several options for future national policies on oxygenated
fuels that will likely stimulate a rapid increase in the
use of ethanol in gasoline, and is also promoting
alternative fuels (e.g., biodiesel) whose behavior in soil
and ground water has not been assessed. EPA is still
developing regulatory guidance for MTBE in drinking water
and surface waters, as well as continuing development of
their proposal to reduce or ban the use of MTBE in
gasoline. Recent US Geological Survey reports have
provided an up-to-date characterization of the occurrence
of MTBE in ambient waters and in drinking water supplies,
and a number of research organizations have been
successful in documenting the biodegradation of MTBE under
a variety of laboratory and field conditions. A clearer
picture is emerging regarding the most effective ways to
characterize MTBE releases, which also provides a better
frame of reference for future risk based decisions on
appropriate corrective action. Contrary to statements in
the popular press, MTBE remediation is not particularly
difficult, as any number of conventional technologies can
be applied. However, it may be expensive, especially if ex
situ treatment to low levels is required of produced
aqueous and vapor phase effluents. It is becoming
increasingly clear that, especially at complex sites, it
is important to develop an accurate conceptual model of
the mass flux of MTBE or other oxygenates from the source
zone.
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