Brad Bessinger, PhD, RG, is a Principal Geochemist aBrad Bessinger, PhD, RG

Principal Geochemist

Camas, Washington


(360) 566-7119

Dr. Brad Bessinger, RG, is a Principal Geochemist and the manager of Summit Water Resources, LLC’s Washington State office. Dr. Bessinger has over 20 years of experience in environmental consulting and is an expert on the geochemistry, fate, and transport of arsenic, metals, radionuclides, and organic contaminants in the environment.

Dr. Bessinger’s consulting practice consists of a wide range of specialized services. One area of expertise is contaminant fate and transport, which can be used to reconstruct historical releases and predict future impacts. Dr. Bessinger has extensive experience developing contaminant fate and transport numerical models, an activity that includes constructing thermodynamic databases, designing field and laboratory studies to parameterize critical geochemical processes, and understanding and evaluating model uncertainty. Dr. Bessinger’s geochemical forward and inverse models have been presented to regulatory agencies to inform on the importance of different contaminant sources, the effects of sediment processes on exposure, and the potential for bioaccumulation. Dr. Brad Bessinger remains actively involved in research and outreach on geochemistry and geochemical modeling, and continues to present and publish on models developed for soil, sediment, water, and groundwater.

Another area of expertise is environmental forensics, which applies scientific and investigative techniques to determine the sources and timing of contamination. Dr. Bessinger has established background concentrations and determined baseline geochemical conditions for litigation and other projects. He has also employed advanced methods such as mineralogical fingerprinting, stable and radiogenic isotope fingerprinting, and chemical fingerprinting to determine the origin of metals, oil and natural gas, chlorinated solvents, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) Dr. Bessinger has completed environmental forensics investigations at industrial facilities nationwide, including mining and smelting sites, petroleum refineries, chemical plants, landfills, and former manufactured gas plants. His findings have been used to defend cost-effective remedial solutions before regulatory agencies, as well as in legal proceedings, such as cost allocations, property and natural resource damage assessments, and personal injury claims.

  • Education

    PhD, Geochemistry, University of California, Berkeley

    MS, Rock Mechanics, University of California, Berkeley

    BS, Engineering Geology, Stanford University

  • Registration / Certification

    Registered Geologist, Oregon

    Licensed Geologist, Washington

  • Specializations

    Soil, sediment, water, and Groundwater geochemistry

    Inorganic Contaminants: Heavy metals; radionuclides; arsenic and selenium; hexavalent chromium; Mercury and methylmercury; Nutrients (nitrate and phosphate); Coal combustion residuals (CCRs)

    Organic Contaminants: Oil and natural gas; chlorinated solvents; PFAS and emerging contaminants; polychlorinated biphenyls (PCBs); polycyclic aromatic hydrocarbons (PAHs)

    Environmental Forensics: Background studies; source assessments; fate and transport analysis; age dating and timing of releases; mineralogical source fingerprinting; stable and radiogenic isotope fingerprinting; chemical fingerprinting (metals, oil/gas, solvents, PAHs, PCBs)

    Contaminant Fate and Transport Modeling: Reactive transport modeling of contaminants in soils and sediments; geochemical modeling peer-review; monitored natural attenuation (MNA) and remediation performance modeling; inverse modeling for source evaluations

  • Affiliations

    National Ground Water Association (NGWA)

    Groundwater Resources Association of California (GRAC)

Select Publications and Presentations

Journal Articles

Bessinger, B., and R. Hennet, 2019. Effectiveness of Monitored Natural Attenuation (MNA) as a Groundwater Remedy for Arsenic in Phosphatic Wastes. Groundwater Monitoring & Remediation, v. 39, pp. 52-68.

Bessinger, B.A., 2014.  The Use of Stable Isotopes to Identify Sources of Mercury in Sediment: A Review and Uncertainty Analysis.  Environmental Forensics, v. 15, pp. 265-280.

Bessinger, B.A., D. Vlassopoulos, S. Serrano, and P.A. O’Day, 2012. Reactive Transport Modeling of Subaqueous Sediment Caps and Implications for the Long-Term Fate of Arsenic, Mercury, and Methylmercury.  Aquatic Geochemistry, v. 18, pp. 297-326.

Serrano, S., D. Vlassopoulos, B. Bessinger, and P.A. O’Day, 2012. Immobilization of Hg(II) by Co-precipitation in Sulfate-Cement Systems. Environmental Science and Technology, v. 46, pp. 6767-6775.

Bessinger, B., and C. Marks, 2010.  Treatment of Mercury-Contaminated Soils with Activated Carbon:  A Laboratory, Field, and Modeling Study.  Remediation Journal, v. 21, no. 1, pp. 115-135.

Bessinger, B., B. Redding, and Y. Lowney, 2007.  Comments on “Release of Arsenic to the Environment from CCA-Treated Wood. 2. Leaching and Speciation During Disposal.”  Environmental Science & Technology, v. 41, no. 1, pp. 345-346.

Shock, S., B. Bessinger, Y. Lowney, and J. Clark, 2007.  Assessment of the Solubility and Bioaccessibility of Barium and Aluminum in Soils Affected by Mine Dust Deposition.  Environmental Science & Technology, v. 41, no. 13, pp. 4813-4820.

Bessinger, B., T. Cooke, B. Foreman, V. Lee, P. Mineart, and L. Armstrong, 2006.  A Kinetic Model of Copper Cycling in San Francisco Bay.  San Francisco Estuary and Watershed Science, v. 4, no. 1.

Mackay, C., M. Johns, J. Salatas, and B. Bessinger, 2006.  Stochastic Probability Modeling to Predict the Environmental Stability of Nanoparticles in Aqueous Suspension.  Integrated Environmental Assessment and Management, v.2, no. 3, pp. 293-298.

Bigham, G., B. Henry, and B. Bessinger, 2005.  Mercury—A Tale of Two Toxins.  Natural Resources & Environment, v. 19, no. 4.  in ABA’s Section of Environment, Energy, and Resources’ Issue on Highly Regulated Chemicals, pp. 26-30.

Bessinger, B., N. Cook, L. Myer, S. Nakagawa, K. Nihei, P. Benito, and R. Suarez-Rivera, 2003.  The Role of Compressive Stress in Jointing on Vancouver Island, British Columbia.  Journal of Structural Geology, v. 25, no. 6, pp. 983-1000.

Bessinger, B., Z. Liu, N. Cook, and L. Myer, 1997.  A New Fracturing Mechanism for Granular Media.  Geophysical Research Letters, v. 24, no. 21, pp. 2605-2608.

Kastenberg, W., P. Peterson, J. Ahn, J. Burch, G. Casher, P. Chambre, E. Greenspan, D. Olander, J. Vujik, B. Bessinger, N. Cook, F. Doyle, and B. Hilbert, 1996.  Considerations of Autocatalytic Criticality in Geologic Repositories. Nuclear Technology, v. 115, pp. 298-308.

Conference Proceedings

Vlassopoulos, D., B. Bessinger, and P. O’Day, 2010.  Aqueous solubility of As2S3 and thermodynamic stability of thioarsenites.  in Proceedings of the Thirteenth International Symposium on Water Rock Interaction.  Guanajuato, Mexico, August 16-20, 2010.

Bessinger, B., D. Vlassopoulos, S. Serrano, and P. O’Day, 2009.  Reactive Transport Modeling of Arsenic and Mercury in a Chemically Amended Sediment Cap.  in Proceedings of the Fifth International Conference on Remediation of Contaminated Sediments, Jacksonville, FL, February 2-5, 2009.

Book Chapters

Bigham, G., B. Henry, and B. Bessinger, 2006. Mercury. in Environmental Forensics, Contaminant Specific Guide.  R. Morrison and B. Murphy, eds.  Amsterdam:  Elsevier Academic Press, pp. 1-17.

Bessinger, B., R. Suarez-Rivers, K. Nihei, B. Hilbert, L. Myer, and N. Cook, 2001.  P-Wave Amplitude Anisotropy in Limestone.  in Advances in Anisotropy: Selected Theory, Modeling, and Case Studies. J. Hood, ed.  Tulsa, OK:  Society of Exploration Geophysicists, 322 pp.


Bessinger, B., D. Brown, A. Butler, M. Chacon, S. Chamberlain, A. Charles, et al., 2010.  A Decision Framework for Applying Monitored Natural Attenuation Processes to Metals and Radionuclides in Groundwater.  Interstate Technology & Regulatory Council, APMR-1, 204 pp.

Bessinger, B., and J. Apps, 2005.  The Hydrothermal Chemistry of Gold, Arsenic, Antimony, Mercury, and Silver.  Lawrence Berkeley National Laboratory, Report No. LBNL-57395.  52 pp.

Bessinger, B., 2000.  The Geochemistry of Gold, Arsenic and Antimony in the Carlin-Type Gold Deposits and the Mechanics of Geologic Fractures.  Lawrence Berkeley National Laboratory, Report No. LBNL-46525.  326 pp.


Bessinger, B. and T. Thompson, 2023. Geochemical Characterization and Reactive Transport Modeling to Evaluate Arsenic in MAR. Presentation at the 2023 National Groundwater Association (NGWA) Managed Aquifer Recharge (MAR) Conference. San Antonio, TX, April 24-25, 2023.

Bessinger, B. and T. Thompson, 2023. Geochemical Modeling for Evaluating Compatibility in Managed Aquifer Recharge Projects. Presentation at the 2023 California Water and Environmental Modeling Forum (CWEMF). Folsom, CA, April 17-19, 2023.

Bessinger, B. and B. Bondy, 2022. The Use of Stable and Radiogenic Isotopes to Understand Groundwater Recharge in the Mound Basin, California. Presentation at 12th Washington Hydrogeology Symposium. Tacoma, WA, May 10-11, 2022.

Bessinger, B., E. Hughes, D. Vlassopoulos, J. Goin, R. Pratt, and R. Healy, 2022. The Fate and Transport of Arsenic in Groundwater Impacted by Slag, Tacoma, WA. Presentation at 12th Washington Hydrogeology Symposium. Tacoma, WA, May 10-11, 2022.

Bessinger, B., P. Rosasco, M. Tonkin, P. Khambhammettu, E. DiFilippo, and M. O’Connell, 2022. Geochemical Characterization to Evaluate the Fate and Transport of Uranium, Thorium, and Radium in a MSW Landfill. Presentation at Fifth Annual Western Groundwater Congress. Sacramento, CA, September 19-21, 2022.

Bessinger, B., T. Thompson, J. Barry, B. Franz, and D. O’Rourke, 2022.  Geochemical Compatibility Considerations in Managed Aquifer Recharge in California. Presentation at Fifth Annual Western Groundwater Congress. Sacramento, CA, September 19-21, 2022.

Bessinger, B., V. Bedekar, M. Tonkin, J. Szecsody, N. Qafoku, and M. Truex, 2015.  Simulation of Co-Precipitated Chromate-Calcite at a Waste Site.  Presentation at MODFLOW and More 2015: Modeling a Complex World, Golden, CO, May 31-June 3, 2015.

Bessinger, B.A., 2012.  Application of Stable Isotopes to Identify Sources of Mercury in the Environment.  Presentation at the 52nd Annual PNWIS/A&WMA Conference, Portland, OR, November 7-9, 2012.

Bessinger, B., and R. Hennet, 2012.  The Effect of Mineralogical Speciation on Arsenic and Boron Mobility in Phosphatic Wastes. Presentation at 22nd Annual International Conference on Soil, Water, Energy, and Air. San Diego, CA, March 19-22, 2012.

Bessinger, B., and D. Vlassopoulos, 2011. A Reactive Transport Model of Mercury Fate in Sediment. Presentation at the 8th Washington Hydrogeology Symposium, Tacoma, WA, April 26-28, 2011.

Vlassopoulos, D., J. Goin, B. Bessinger, C. Kiehl-Simpson, and E. Glaza, 2011.  Evaluation of pH-Buffering Amendments for In Situ Capping of Hyperalkaline Contaminated Sediments.  Presentation at 6th International Conference on Remediation of Contaminated Sediments.  New Orleans, LA, February 7-10, 2011.

Bessinger, B., D. Vlassopoulos, S. Serrano, and P. O’Day, 2010.  Reactive Transport Modeling of Arsenic and Mercury Fate at the Ground Water-Surface Water Interface.  Presentation at the 2010 Ground Water Summit, Denver, CO, April 11-15, 2010.

Bessinger, B., and D. Vlassopoulos, 2009.  A Geochemical Reactive Transport Model of Arsenic and Trihalomethanes in Aquifer Storage & Recovery Systems.  Presentation at the 7th Washington Hydrogeology Symposium, Tacoma, WA, April 27-30, 2009.

Vlassopoulos, D., B. Bessinger, V. Illera, and P. O’Day, 2009.  Lithologic, Hydrologic and Biogeochemical Influences on Spatio-Temporal Variability of As and Hg Concentrations in Groundwater.  Presentation at Goldschmidt 2009, Davos, Switzerland, June 21-26, 2009.

O’Day, P., S. Serrano, B. Bessinger, V. Illera, and D. Vlassopoulos, 2009.  Sediment Remediation of Metal and Metalloid Contaminants with Reactive Amendments.  Presentation at Goldschmidt 2009, Davos, Switzerland, June 21-26, 2009.

Serrano, S., P. O’Day, B. Bessinger, and D. Vlassopoulos, 2009.  Immobilization of Mercury(II) by Ettringite-Type Phases: Modeling and Experiments.  Presentation at the Geological Society of America Annual Meeting, Portland, OR, October 18-21, 2009.

Bessinger, B., and F. Mohsen, 2008.  Simulation of Tidal Effects on Contaminant Fate and Transport near the Sediment-Water Interface.  Presentation at Pacific Northwest Society of Environmental Toxicology and Chemistry (PNW-SETAC) Annual Meeting, Corvallis, OR, March 27-29, 2008.

Bessinger, B., 2006.  Introduction to the Environmental Forensics of PAHs.  Presentation at the Northwest Environmental Conference, Northwest Environmental Business Council, Portland, OR, December 7-8, 2006.

Bessinger, B., 2005.  Source Apportionment Methods for Lead in Residential Soils near a Former Zinc Smelter.  Presentation at the Pacific Northwest International Section 2005 – Air and Waste Management Association, Blaine, WA, November 8-11, 2005.

Short Courses

Bessinger, B., 2019. Geochemical Modeling for Project Managers. Presentation of Short Course to Electric Power Research Institute (EPRI), Columbus, OH, August 22, 2019.

Bessinger, B., and C. Neville, 2015.  Solute Transport Modeling: Ideal and Otherwise.  Presentation of Short Course at the 10th Washington Hydrogeology Symposium, Tacoma, WA, April 14-16, 2015.