Gary Curtis (Former Employee)
Science and Products
Filter Total Items: 27
Influence of variable chemical conditions on EDTA-enhanced transport of metal ions in mildly acidic groundwater
Adsorption of Ni and Pb on aquifer sediments from Cape Cod, Massachusetts, USA increased with increasing pH and metal-ion concentration. Adsorption could be described quantitatively using a semi-mechanistic surface complexation model (SCM), in which adsorption is described using chemical reactions between metal ions and adsorption sites. Equilibrium reactive transport simulations incorporating the
Authors
D.B. Kent, J.A. Davis, J.L. Joye, G.P. Curtis
Research activities at U.S. Government agencies in subsurface reactive transport modeling
The fate of contaminants in the environment is controlled by both chemical reactions and transport phenomena in the subsurface. Our ability to understand the significance of these processes over time requires an accurate conceptual model that incorporates the various mechanisms of coupled chemical and physical processes. Adsorption, desorption, ion exchange, precipitation, dissolution, growth, sol
Authors
Randall T. Cygan, Caroline T. Stevens, Robert W. Puls, Steven B. Yabusaki, Robert D. Wauchope, Christian J. McGrath, Gary P. Curtis, Malcolm D. Siegel, Linda A. Veblen, David R. Turner
Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions
The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KDvalues decreased with increasing U(VI) and alkalini
Authors
Gary P. Curtis, James A. Davis, David L. Naftz
Processes affecting transport of uranium in a suboxic aquifer
At the Naturita site in Colorado, USA, groundwaters were sampled and analyzed for chemical composition and by culture and culture-independent microbiological techniques. In addition, sediments were extracted with a dilute sodium carbonate solution to determine quantities of labile uranium within the sediments. Samples from the upgradient portion of the contaminated aquifer, where very little disso
Authors
J.A. Davis, G.P. Curtis, M.J. Wilkins, M. Kohler, P. Fox, D. L. Naftz, J.R. Lloyd
Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials
The fate of arsenic in groundwater depends largely on its interaction with mineral surfaces. We investigated the kinetics of As(III) oxidation by aquifer materials collected from the USGS research site at Cape Cod, MA, USA, by conducting laboratory experiments. Five different solid samples with similar specific surface areas (0.6–0.9 m2 g−1) and reductively extractable iron contents (18–26 μmol m−
Authors
A. Amirbahman, D.B. Kent, G.P. Curtis, J.A. Davis
Review of the transport of selected radionuclides in the interim risk assessment for the Radioactive Waste Management Complex, Waste Area Group 7 Operable Unit 7-13/14, Idaho National Engineering and Environmental Laboratory, Idaho
The U.S. Department of Energy (DOE) requested that the U.S. Geological Survey conduct an independent technical review of the Interim Risk Assessment (IRA) and Contaminant Screening for the Waste Area Group 7 (WAG-7) Remedial Investigation, the draft Addendum to the Work Plan for Operable Unit 7-13/14 WAG-7 comprehensive Remedial Investigation and Feasibility Study (RI/FS), and supporting documents
Authors
Joseph P. Rousseau, Edward R. Landa, John R. Nimmo, L. DeWayne Cecil, LeRoy L. Knobel, Pierre D. Glynn, Edward M. Kwicklis, Gary P. Curtis, Kenneth G. Stollenwerk, Steven R. Anderson, Roy C. Bartholomay, Clifford R. Bossong, Brennon R. Orr
A simple method for calculating growth rates of petroleum hydrocarbon plumes
Consumption of aquifer Fe(III) during biodegradation of ground water contaminants may result in expansion of a contaminant plume, changing the outlook for monitored natural attenuation. Data from two research sites contaminated with petroleum hydrocarbons show that toluene and xylenes degrade under methanogenic conditions, but the benzene and ethylbenzene plumes grow as aquifer Fe(III) supplies ar
Authors
B.A. Bekins, I.M. Cozzarelli, G.P. Curtis
Assessing conceptual models for subsurface reactive transport of inorganic contaminants
In many subsurface situations where human health and environmental quality are at risk (e.g., contaminant hydrogeology petroleum extraction, carbon sequestration, etc.),scientists and engineers are being asked by federal agency decision-makers to predict the fate of chemical species under conditions where both reactions and transport are processes of first-order importance.In 2002, a working group
Authors
James A. Davis, Steven B. Yabusaki, Carl Steefel, John M. Zachara, Gary P. Curtis, George D. Redden, Louise J. Criscenti, Bruce D. Honeyman
Comparison of in situ uranium KD values with a laboratory determined surface complexation model
Reactive solute transport simulations in groundwater require a large number of parameters to describe hydrologic and chemical reaction processes. Appropriate methods for determining chemical reaction parameters required for reactive solute transport simulations are still under investigation. This work compares U(VI) distribution coefficients (i.e. KD values) measured under field conditions with KD
Authors
G.P. Curtis, P. Fox, M. Kohler, J.A. Davis
Methods for estimating adsorbed uranium(VI) and distribution coefficients of contaminated sediments
Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydrox
Authors
M. Kohler, G.P. Curtis, D.E. Meece, J.A. Davis
Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments
Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the
Authors
J.A. Davis, D.E. Meece, M. Kohler, G.P. Curtis
Comparison of approaches for simulating reactive solute transport involving organic degradation reactions by multiple terminal electron acceptors
Reactive solute transport models are useful tools for analyzing complex geochemical behavior resulting from biodegradation of organic compounds by multiple terminal electron acceptors (TEAPs). The usual approach of simulating the reactions of multiple TEAPs by an irreversible Monod rate law was compared with simulations that assumed a partial local equilibrium or kinetically controlled reactions s
Authors
Gary P. Curtis
Science and Products
Filter Total Items: 27
Influence of variable chemical conditions on EDTA-enhanced transport of metal ions in mildly acidic groundwater
Adsorption of Ni and Pb on aquifer sediments from Cape Cod, Massachusetts, USA increased with increasing pH and metal-ion concentration. Adsorption could be described quantitatively using a semi-mechanistic surface complexation model (SCM), in which adsorption is described using chemical reactions between metal ions and adsorption sites. Equilibrium reactive transport simulations incorporating the
Authors
D.B. Kent, J.A. Davis, J.L. Joye, G.P. Curtis
Research activities at U.S. Government agencies in subsurface reactive transport modeling
The fate of contaminants in the environment is controlled by both chemical reactions and transport phenomena in the subsurface. Our ability to understand the significance of these processes over time requires an accurate conceptual model that incorporates the various mechanisms of coupled chemical and physical processes. Adsorption, desorption, ion exchange, precipitation, dissolution, growth, sol
Authors
Randall T. Cygan, Caroline T. Stevens, Robert W. Puls, Steven B. Yabusaki, Robert D. Wauchope, Christian J. McGrath, Gary P. Curtis, Malcolm D. Siegel, Linda A. Veblen, David R. Turner
Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions
The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KDvalues decreased with increasing U(VI) and alkalini
Authors
Gary P. Curtis, James A. Davis, David L. Naftz
Processes affecting transport of uranium in a suboxic aquifer
At the Naturita site in Colorado, USA, groundwaters were sampled and analyzed for chemical composition and by culture and culture-independent microbiological techniques. In addition, sediments were extracted with a dilute sodium carbonate solution to determine quantities of labile uranium within the sediments. Samples from the upgradient portion of the contaminated aquifer, where very little disso
Authors
J.A. Davis, G.P. Curtis, M.J. Wilkins, M. Kohler, P. Fox, D. L. Naftz, J.R. Lloyd
Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials
The fate of arsenic in groundwater depends largely on its interaction with mineral surfaces. We investigated the kinetics of As(III) oxidation by aquifer materials collected from the USGS research site at Cape Cod, MA, USA, by conducting laboratory experiments. Five different solid samples with similar specific surface areas (0.6–0.9 m2 g−1) and reductively extractable iron contents (18–26 μmol m−
Authors
A. Amirbahman, D.B. Kent, G.P. Curtis, J.A. Davis
Review of the transport of selected radionuclides in the interim risk assessment for the Radioactive Waste Management Complex, Waste Area Group 7 Operable Unit 7-13/14, Idaho National Engineering and Environmental Laboratory, Idaho
The U.S. Department of Energy (DOE) requested that the U.S. Geological Survey conduct an independent technical review of the Interim Risk Assessment (IRA) and Contaminant Screening for the Waste Area Group 7 (WAG-7) Remedial Investigation, the draft Addendum to the Work Plan for Operable Unit 7-13/14 WAG-7 comprehensive Remedial Investigation and Feasibility Study (RI/FS), and supporting documents
Authors
Joseph P. Rousseau, Edward R. Landa, John R. Nimmo, L. DeWayne Cecil, LeRoy L. Knobel, Pierre D. Glynn, Edward M. Kwicklis, Gary P. Curtis, Kenneth G. Stollenwerk, Steven R. Anderson, Roy C. Bartholomay, Clifford R. Bossong, Brennon R. Orr
A simple method for calculating growth rates of petroleum hydrocarbon plumes
Consumption of aquifer Fe(III) during biodegradation of ground water contaminants may result in expansion of a contaminant plume, changing the outlook for monitored natural attenuation. Data from two research sites contaminated with petroleum hydrocarbons show that toluene and xylenes degrade under methanogenic conditions, but the benzene and ethylbenzene plumes grow as aquifer Fe(III) supplies ar
Authors
B.A. Bekins, I.M. Cozzarelli, G.P. Curtis
Assessing conceptual models for subsurface reactive transport of inorganic contaminants
In many subsurface situations where human health and environmental quality are at risk (e.g., contaminant hydrogeology petroleum extraction, carbon sequestration, etc.),scientists and engineers are being asked by federal agency decision-makers to predict the fate of chemical species under conditions where both reactions and transport are processes of first-order importance.In 2002, a working group
Authors
James A. Davis, Steven B. Yabusaki, Carl Steefel, John M. Zachara, Gary P. Curtis, George D. Redden, Louise J. Criscenti, Bruce D. Honeyman
Comparison of in situ uranium KD values with a laboratory determined surface complexation model
Reactive solute transport simulations in groundwater require a large number of parameters to describe hydrologic and chemical reaction processes. Appropriate methods for determining chemical reaction parameters required for reactive solute transport simulations are still under investigation. This work compares U(VI) distribution coefficients (i.e. KD values) measured under field conditions with KD
Authors
G.P. Curtis, P. Fox, M. Kohler, J.A. Davis
Methods for estimating adsorbed uranium(VI) and distribution coefficients of contaminated sediments
Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydrox
Authors
M. Kohler, G.P. Curtis, D.E. Meece, J.A. Davis
Approaches to surface complexation modeling of Uranium(VI) adsorption on aquifer sediments
Uranium(VI) adsorption onto aquifer sediments was studied in batch experiments as a function of pH and U(VI) and dissolved carbonate concentrations in artificial groundwater solutions. The sediments were collected from an alluvial aquifer at a location upgradient of contamination from a former uranium mill operation at Naturita, Colorado (USA). The ranges of aqueous chemical conditions used in the
Authors
J.A. Davis, D.E. Meece, M. Kohler, G.P. Curtis
Comparison of approaches for simulating reactive solute transport involving organic degradation reactions by multiple terminal electron acceptors
Reactive solute transport models are useful tools for analyzing complex geochemical behavior resulting from biodegradation of organic compounds by multiple terminal electron acceptors (TEAPs). The usual approach of simulating the reactions of multiple TEAPs by an irreversible Monod rate law was compared with simulations that assumed a partial local equilibrium or kinetically controlled reactions s
Authors
Gary P. Curtis