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EPA/600/F 09/003 

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 nearsurface 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 metalcarbonate 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 
 

pose the greatest risk and 

indicate the need for more 

detailed chemical analyses. 

 Experimental Verification 

Experimental studies will 

make use of highpressure/high-temperature 

reactors for examining 

element partitioning between 

aquifer solids and water over 

a range of CO2 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 CO2 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 CO2 

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@epa.gov 

Dominic C. DiGiulio, Ph.D., EPA’s Office of 

Research and Development, U.S. Environmental 

Protection Agency, 580-436-8605, 

digiulio.dominic@epa.gov 

Robert W. Puls, Ph.D., EPA’s Office of Research 

and Development, U.S. Environmental Protection 

Agency, 580-436-8543, puls.robert@epa.gov 

Audrey D. Levine, Ph.D., EPA’s National Program 

Director, Drinking Water Research Program 

202-564-1070, levine.audrey@epa.gov