USGS - science for a changing world

USGS Professional Pages

Blank space
Search USGS Professionals Featured Profiles Blank space Frequently Asked Questions  |  About The USGS Professional Pages
bio image of Gary  Curtis

Gary Curtis

Environmental Engineer

Contact Info

Short Biography

Research Interests:

Gary Curtis is a hydrogeochemist who develops and applies reactive transport models to simulate groundwater contamination problems involving hexavalent uranium (U(VI)) and chloroethenes.  His research interests include:

  • Developing and applying conceptual models for simulating reactive transport processes in groundwater;
  • Conducting nonreactive and reactive tracer tests to characterize subsurface physical heterogeneity and effective reactive processes;
  • Quantifying prediction uncertainty inherent in all reactive transport models;and,

Developing upscaled reactive transport models that can be applied to real-world plume scale simulations that honor detailed understanding developed from small scale laboratory and field tracer tests.


Lu, D., Ye, M. and Curtis, G.P. 2015. Maximum likelihood Bayesian model averaging and its predictive analysis for groundwater reactive transport models. Journal of Hydrology, 529, 1859-1873. [Link]

Shi, X., M. Ye, G. P. Curtis, G. L. Miller, P. D. Meyer, M. Kohler, S. Yabusaki, and J. Wu (2014), Assessment of parametric uncertainty for groundwater reactive transport modeling, Water Resour. Res., 50, 4416–4439, doi:10.1002/2013WR013755. [Link]

Dan Lu, Ming Ye, Mary C. Hill, Eileen P. Poeter, Gary P. Curtis,2014, A computer program for uncertainty analysis integrating regression and Bayesian methods, Environmental Modelling & Software, Vol60,45-56. [Link]

Briggs,MA, FD Day-Lewis, JBT Ong, GP Curtis, JW Lane, 2013,Simultaneous estimation of local-scale and flow path-scale dual-domain mass transfer parameters using geoelectrical monitoring, Water Resources Research 49 (9), 5615-5630. [Link]

D Lu, M Ye, PD Meyer, GP Curtis, X Shi, XF Niu, SB Yabusaki, 2013, Effects of error covariance structure on estimation of model averaging weights and predictive performance, Water Resources Research 49 (9), 6029-6047. [Link]

A Amirbahman, DB Kent, GP Curtis, MC Marvin-DiPasquale, 2013, Kinetics of homogeneous and surface-catalyzed mercury (II) reduction by iron (II), Environmental science & technology 47 (13), 7204-7213. [Link]

TR Brosten, FD Day-Lewis, GM Schultz, GP Curtis, JW Lane Jr, 2011, Inversion of multi-frequency electromagnetic induction data for 3D characterization of hydraulic conductivity, Journal of Applied Geophysics 73 (4), 323-335. [Link]

Curtis, G.P., Kohler, M., Davis, J.A. Comparing Approaches for Simulating the Reactive Transport of U(VI) in Ground Water, 2009, Mine Water and the Environment, 28:84-93. [Link]

Kent, D.B., Davis, J.A., Joye, J.L., Curtis, G.P., 2008, Influence of variable chemical conditions on EDTA-enhanced transport of metal ions in mildly acidic groundwater, Environmental Pollution, 153(1):44-52. [Link]

Cygan, R.T., Stevens, C.T., Puls, R.W., Yabusaki, S.B., Wauchope, R.D., McGrath, C.J., Curtis, G.P., Siegel, M.D., Veblen, L.A., Turner, D.R., 2007, Research activities at U.S. government agencies in subsurface reactive transport modeling, Vadose Zone Journal, 6 (4):805-822. [Link]

Davis, J.A., Curtis, G.P., Wilkins, M.J., Kohler, M., Fox, P.M., Naftz, D.L., and Lloyd, J.R., 2006, Processes affecting transport of uranium in a suboxic aquifer: Physics and Chemistry of the Earth, 31:548-555.

Curtis, G.P., Davis, J.A., and Naftz, D.L., 2006, Simulation of reactive transport of uranium(VI) in groundwater with variable chemical conditions: Water Resources Research, v. 42, no. 4, W04404, doi: 10.1029/2005WR003979. [Link]

Amirbahman, A., Kent, D.B., Curtis, G.P., and Davis, J.A., 2006, Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials: Geochimica et Cosmochimica Acta, 70: 533-547. [Link]

Bekins, B. A., Cozzarelli, I.M., and Curtis, G.P., 2005, A simple method for calculating growth rates of petroleum hydrocarbon plumes: Ground Water, 43:817-826. [Link]

Curtis, G.P., Fox, P., Kohler, M., and Davis, J.A., 2004, Comparison of in situ uranium Kd values with a laboratory determined surface complexation model: Applied Geochemistry, 19:1,643-1,653. [Link]

Kohler, M., Curtis, G.P.,Meece, D.E., and Davis, J.A., 2004, Methods for estimating adsorbed uranium(VI) and distribution coefficients in contaminated sediments, Environ.Sci.Technol., 34:240-247. [Link]

Davis, J.A., Yabusaki, S.B., Steefel, C.I., Zachara, J.M., Curtis, G.P., Redden, G.P., Criscenti, L.J., and Honeyman, B.D., 2004, Assessing Conceptual Models for Subsurface Reactive Transport of Inorganic Contaminants: EOS, 85(44): 449 and 455.

Davis, J.A., Meece, D.E., Kohler, M., and Curtis, G.P., 2004, Approaches to surface complexation modeling of uranium(VI) adsorption on aquifer sediments: Geochimica et Cosmochimica Acta, 68:3,621-3,641. [Link]

Curtis, G.P., 2003. Comparison of approaches for simulating reactive solute transport involving organic degradation reactions by multiple terminal electron acceptors, Computers in Geosciences, 18(3):319-329. [Link]

Kohler, M., Curtis, G. P.; Kent, D. B., and Davis, J. A., 1996, Experimental investigation and modeling of uranium(VI) transport under variable chemical conditions. Water Resources Research, 32(12):3539-3552. [Link]

Previous Publications

Powell, R.M., Bledsoe, B.E., Curtis, G.P. and Johnson, R.M., 1989, Interlaboratory methods comparison for the total organic carbon analysis of aquifer material: Environmental Science and Technology.  23(10):1246-1251.

Curtis, G.P., Roberts, P.V., and Reinhard, M., 1986, A natural gradient experiment on solute transport in a sand aquifer: IV. Sorption of organic solutes and its influence on mobility: Water Resources Research.  22(13):2059-2067.

Book Chapters

Curtis, G.P., and Davis, J.A., 2004, Simulation of U(VI) transport in groundwater with variable geochemical conditions, in Wanty, R.B., and Seal, R.R., II, eds., Water-Rock Interaction, Proceedings of the Eleventh International Symposium on Water-Rock Interaction, Saratoga Springs, New York, July 2004: New York, A.A. Balkema, v. 2, p. 927-933.

Reinhard, M., Curtis, G.P., and Barbash, J.E., 1997. Natural chemical attenuation of halogenated hydrocarbon compounds via dehalogenation. In: C.H.Ward, J.A.Cherry and M.R. Scalf, eds, Subsurface Restoration. Ann Arbor Press, Chelsea, MI., p 397-409.

Ball, W.P., Curtis, G.P., and Roberts, P.V., 1997. Physical/Chemical Processes affecting the subsurface fate and transport of synthetic organic materials.  In: C.H.Ward, J.A.Cherry and M.R. Scalf, eds, Subsurface Restoration. Ann Arbor Press, Chelsea, MI., p 27-58.

Curtis, G.P., Reinhard, M., and Roberts, P.V., 1986, Sorption of hydrophobic organic compounds by sediments. in: J.A. Davis and K.F.Hayes, eds., Geochemical Processes at Mineral Surfaces. ACS Symposium Series 323, American Chemical Society, Washington D.C., p. 191-216.


Technical Reports

Davis, J.A. and G.P. Curtis, 2007, Consideration of Geochemical Issues in Groundwater Report NUREG CR-6870, U.S. Nuclear Regulatory Commission, Rockville, MD, 150 p.

Curtis, G.P. and Davis, J.A., 2006, Tests of Uranium(VI) Adsorption Models in a Field Setting, Report NUREG CR-6911, U.S. Nuclear Regulatory Commission, Rockville, MD, 99 p.

Curtis, G.P., 2005, Documentation and Applications of the Reactive Geochemical Transport Model RATEQ, Report NUREG CR-6871, U.S. Nuclear Regulatory Commission, Rockville, MD, 97 p.

 Rousseau, J.P., Landa, E.R., Nimmo, J.R., Cecil, L.D., Knobel, L.L., Glynn, P.D., Kwicklis, E.M., Curtis, G.P., Stollenwerk, K.G., Anderson, S.R., Bartholomay, R.C., Bossong, C.R., and Orr, B.R., 2005, 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: U.S. Geological Survey Scientific Investigations Report 2005-5026, 283 p. in 2 volumes. 

Davis, J.A., and Curtis, G.P., 2003, Application of Surface Complexation Modeling to Describe Uranium(VI) Adsorption and Retardation at the Uranium Mill Tailings Site at Naturita, Colorado: US Nuclear Regulatory Commission, NUREG/CR-6708, 238p. 

Curtis, G.P., Cozzarelli, I.M., Baedecker, M.J., Bekins, B.A., 1999. Coupled biogeochemical modeling of ground water contamination at the Bemidji, Minnesota, crude oil spill site, in Morganwalp, D.W., and Buxton, H.T., eds., U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Charleston, South Carolina, March 8-12, 1999--Volume 3 of 3--Subsurface Contamination from Point Sources: U.S. Geological Survey Water-Resources Investigations Report 99-4018C, p. 153-158.


My Science Topics

Science Topic
Water Resourcesground water
Water Resourcesground-water quality
Environmental Issuescontamination and pollution
Environmental Issuesground-water quality
Environmental Issuestoxic radionuclides
Environmental Issuestoxic trace elements
Techniques and Methodsmathematical modeling

Field Research Sites

Naturita UMTRA Site 


Statement of Problem:

Groundwater contamination from hexavalent uranium U(VI) is a problem at many federal sites because of its importance in the nuclear fuel cycle. The adsorption and therefore mobility of U(VI) in groundwater is controlled by the local geochemical conditions such as pH and especially the alkalinity which is usually composed primarily of bicarbonate and carbonate ions. Understanding the mobility of U(VI) in groundwater is a key prerequisite to estimating the discharge to receiving water bodies, quantifying risks from the use of contaminated groundwater and evaluating site management alternatives.



Field Site Description:

This research is being conducted at the Naturita UMTRA site located 3km north of Naturita CO.  Uranium ores were processed at the site beginning in 1940.  Tailing and process water were disposed on site resulting in uranium concentrations up to 2300ug/L (10uM) in the shallow alluvial aquifer beneath the site.  A more complete description of the site is available in Davis and Curtis (2004) and Curtis et al (2006). 


See Site in Google Maps. Site Location 



The objectives of this research is to develop and demonstrate scientifically informed and defensible approaches for simulating U(VI) transport in aquifers with variable geochemical conditions.  These objectives have been addressed by conducting laboratory bench scale studies, small scale field tests and plume scale monitoring.



Significant results at the Naturita site include:

  • Development of semi-mechanistic surface complexation model to simulate U(VI) adsorption by uncontaminated sediments collected from an upgradient of the former mill site (Davis et al., 2004).
  • Development and application of a carbonate extraction method to quantify U(VI) adsorption by contaminated sediments collected during well installation (Kohler et al, 2004).
  • The semi-mechanistic surface complexation model predicted the in situ adsorption of U(VI) by samples of uncontaminated sediments suspended in wells with varying U(VI) concentration and alkalinity (Curtis et al., 2004).
  • A reactive transport model that used the semi-mechanistic surface complexation model could reproduce the observed temporal and spatial distributions of U(VI) in the aquifer (Curtis et al., 2006).
  • Localized geochemical reducing conditions exist in a small portion of the aquifer and that these sediment likely contained small concentrations of reduced uranium (U(IV)) (Davis et al., 2006).
  • Application of the surface complexation modeling approach successfully simulated U(VI) adsorption and desorption in small scale tracer tests with variable alkalinity (Curtis and Davis, 2007).
  • Comparing the reactive transport simulations using the simplistic Kd approach with the surface complexation approach (Curtis et al., 2009).



Current Research Activities at the Naturita Site:
Two related research projects are being conducted at the site and are focused on two fundamental questions.  The first project, “Multi-scale Assessment of Prediction Uncertainty in Coupled Reactive Transport Models” aims assess (1) the relative importance of conceptual versus parametric uncertainty in reactive transport models, (2) how conceptual and parametric uncertainty varies across multiple scales, and (3) evaluating which new data should be collected to reduce prediction uncertainty.

The second project, “Upscaling of U(VI) Desorption and Transport from Decimeter-Scale Heterogeneity to Plume-Scale Modeling” is focused on developing and demonstrating quantitative approaches for incorporating small-scale information on uranium desorption rates on plume scale behaviors.



Funding Agencies:

We gratefully acknowledge the support of our funding agencies

1994-2004  US Nuclear Regulatory Commission, Office of Nuclear Regulatory Research

2005-2010  US Department of Energy Subsurface Biogeocemical Research

Contact Information

Gary Curtis
345 Middlefield Road
Menlo Park, CA 94025
650-329-4327 - Fax
Back to top

Accessibility FOIA Privacy Policies and Notices logo U.S. Department of the Interior | U.S. Geological Survey
Page Contact Information:Ask USGS
Page Last Modified: November 02 2016 11:49:34.
Version: 2.6