ŁEPA
www.epa.gov/ord
                                                                            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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    U.S. Environmental Protection Agency
    Office of Research and Development

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&EPA
www.epa.gov/ord
                        DRINKING  WATER  RESEARCH   PROGRAM
         continued from from
         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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