John Bargar, SLAC National Accelerator Laboratory, Stanford Synchrotron Radiation Lightsource, Menlo Park, CA, United States, Christian Dewey, Stanford University, Department of Earth System Science, Stanford, CA, United States, Bradley B Tolar, Stanford University, Earth System Science, Stanford, CA, United States; SLAC National Accelerator Laboratory, Geochemistry and Biogeochemistry, Menlo Park, CA, United States, Scarlet-Marie Kilpatrick, Stanford University, Earth System Sciences, Stanford, CA, United States, Andrew H Manning, USGS Colorado Water Science Center Lakewood, Lakewood, CO, United States and Kenneth Hurst Williams, Lawrence Berkeley National Laboratory, Earth and Environmental Sciences, Berkeley, CA, United States