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John Bargar
Environmental Science Area Leader

Dr. John Bargar is the Environmental Transformations and Interactions Science Area leader. His research interest focuses on molecular processes across molecular to pore to field scales that provide new insights into building new tools and models to better understand and simulate Earth system behavior.

For more than 25 years, Bargar has led projects pertaining to both molecular structure and system-scale research with respect to the behavior of essential metal micronutrients and metal contaminants in soils and natural waters. At the molecular level, his research has contributed important findings and models of metal behavior in soils and groundwater. Coordinated laboratory and field work conducted by Bargar and his team discovered that uranium behavior in contaminated soils at legacy DOE sites is controlled by short seasonal “hot moments” when water tables and dissolved oxygen are elevated. At the larger systems scale, his research has focused on understanding how, where, and when molecular reactions occur and interact across larger distances, from floodplains to regions. For example, laboratory model studies coordinated with field sampling performed by Bargar’s team showed that soil organic matter interactions control uranium accumulation and release in soils across the entire upper Colorado River Basin, where these interactions moderate persistent uranium groundwater contamination.

Before joining PNNL in 2022, Bargar led the SLAC National Accelerator Laboratory geosciences program, including the SLAC National Accelerator Laboratory Floodplain Hydro-Biogeochemistry Sciences Focus Area project, the SLAC-led multi-laboratory nuclear forensics research program, and the SLAC deep subsurface geochemistry project.

Bargar has participated as a reviewer for numerous geochemistry, hydrology, and chemistry journals, has chaired and organized numerous committees and symposia, and has been published in more than 190 scholarly articles.

Research Interests

  • Soil molecular processes across molecular to pore to field scales
  • Biogeochemistry, genesis, and transport of natural colloids
  • Metal micronutrient and contaminant biogeochemistry and reactive transport in soils
  • Water–rock interactions


  • PhD in Geology, The Ohio State University
  • BS in Geological and Environmental Sciences, Stanford University
  • National Research Council Postdoctoral Fellowship, U.S. Geological Survey
  • SLAC Managerial Skill Development Series