ŁEPA
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EPA/600/F 09/003
science in ACTION
DRINKING WATER RESEARCH
PROGRAM
UNDERSTANDING GEOCHEMICAL IMPACTS OF CARBON DIOXIDE LEAKAGE
FROM CARBON CAPTURE AND SEQUESTRATION
Issue:
Carbon capture and sequestration
(CCS) in the earth's subsurface
can potentially offset global CO2
emissions derived from the
combustion of fossil fuels.
Research and development of
CCS technology encompasses a
wide range of issues to
investigate collection of CO2
from emission streams, transport
of CO2, injection into deep
geological environments, and
tracking the long-term fate of
CO2 in the subsurface.
Even with the large physical
separation between storage
reservoirs and surficial
environments, there remains
concern that CO2 stored in
reservoirs may eventually leak
back to the surface through
abandoned wells or along
geological features such as faults.
Leakage would reduce the
effectiveness of CCS, possibly
lead to human health and
ecological impacts at the ground
surface, and possibly harmfully
impact water quality of near-
surface aquifers used for drinking
water.
Scientific Objective:
The U.S. Environmental
Protection Agency's (EPA) Water
Research Program in the Office
of Research and Development is
conducting research to better
understand the geochemical
consequences of CO2 leakage into
ground water. The research is
part of the program's effort at
protecting the quality and
sustainability of water resources.
Leakage of CO2 into ground
water could result in decreased
pH, increased mineral dissolution,
and possible release of metal and
metalloid contaminants. On the
other hand, increases in CO2
concentrations could also result in
increased attenuation of certain
metals and act to retard
contaminant migration.
Geochemical causes of
contaminant mobilization are
expected to result from a
combination of low pH
dissolution of mineral hosts,
enhanced solubility due to metal-
carbonate complexation, and/or
desorption of metals from mineral
surfaces. Attenuation processes
involve sequestration via
carbonate mineral precipitation
and sorption, particularly of
anionic contaminants at the
mineral-water interface.
Research is focused in three
topical areas:
. Geochemical Modeling
Research is conducted to
advance the application of
geochemical modeling that
can be used as a predictive
tool for evaluating risks to
water quality. Developing
modeling procedures will help
to identify contaminants that
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Office of Research and Development
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DRINKING WATER RESEARCH PROGRAM
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pose the greatest risk and
indicate the need for more
detailed chemical analyses.
. Experimental Verification
Experimental studies will
make use of high-
pressure/high-temperature
reactors for examining
element partitioning between
aquifer solids and water over
a range of CC>2 partial
pressures. This type of
experimental system is well
suited for studying the
kinetics of mineral-water
reactions as well as testing
predictions from geochemical
models.
. Natural Analogs
Projects evaluate instances
where natural processes have
generated high CC>2 levels in
ground water and interpret
geochemical observations
from these unique natural
analogs.
The National Risk Management
Research Laboratory (NRMRL)
has a long history of conducting
research on metal speciation,
transport and fate, and
contaminant remediation in
ground-water systems. One
aspect of this research examines
the assimilative capacity of
natural environments to attenuate
inorganics and hydrocarbons (U.S
EPA, 2007a, 2007b). Research
conducted to better understand
impacts stemming from CC>2
leakage builds upon previous
efforts in the area of contaminant
behavior in ground-water systems
and takes advantage of in-house
expertise and infrastructure in
contaminant hydrogeology.
Application and Impact:
Assessing the risk of carbon
dioxide leaking out of storage
units and the consequences
thereof is one of the most
important and demanding tasks
for assuring that geologic storage
projects are safe and effective
(Benson, 2005; Wilson et al.,
2007).
The outcomes of this research,
conducted through the Drinking
Water Research program, will be
implemented in an adaptive
approach for developing
regulations for CCS that allows
EPA to establish regulations to
protect underground supplies of
drinking water (USDWs), and
enable changes to regulations
over time as information from
demonstration projects and other
studies becomes available.
REFERENCES:
Benson, S.M. (2005). Risk assessment preface. In
Carbon Dioxide Capture for Storage in Deep
Geologic Formations — Results from the CO2
Capture Project. Volume 2: Geologic Storage with
Monitoring and Verification, Elsevier.
U.S. EPA (2007a). Monitored Natural Attenuation
of Inorganic Contaminants in Ground Water:
Volume 1, Technical Basis for Assessment, EPA
Report, EPA/600/R07/139.
(http://www.epa.gov/ada/pubs/reports.html)
U.S. EPA (2007b). Monitored Natural Attenuation
of Inorganic Contaminants in Ground Water:
Volume 2, Assessment for Non-radionuclides
Including Arsenic, Cadmium, Chromium, Copper,
Lead, Nickel, Nitrate, Perchlorate, and Selenium,
EPA Report, EPA/600/R07/140.
(http://www.epa.gov/ada/pubs/reports.html)
Wilson, E.J., Friedmann, S.J., and Pollak, M.F.
(2007). Research for deployment: Incorporating
risk, regulation, and liability for carbon capture
and sequestration. Environmental Science and
Technology, v. 41, p. 5945-5952.
CONTACTS:
Richard T. Wilkin, Ph.D., EPA's Office of
Research and Development, U.S. Environmental
Protection Agency, 580-436-8874,
wilkin.rick(g!epa. gov
Dominic C. DiGiulio, Ph.D., EPA's Office of
Research and Development, U.S. Environmental
Protection Agency, 580-436-8605,
di giulio. dominic(g!epa. gov
Robert W. Puls, Ph.D., EPA's Office of Research
and Development, U.S. Environmental Protection
Agency, 580-436-8543, puls.robert(g!epa.gov
Audrey D. Levine, Ph.D., EPA's National Program
Director, Drinking Water Research Program
202-564-1070, levine.audrevfiiepa.gov
U.S. Environmental Protection Agency
Office of Research and Development
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