National Water Quality Assessment Project DGMETA (Version 1): Dissolved Gas Modeling and Environmental Tracer Analysis Computer Program Noble gases Fractionated 0.1 Helium 35 excess air Neon 0 Argon 10 Krypton 30 8 6 Xenon 10 Temperature 4 Reactive gases 25 20 2 0.01 Nitrogen 30 0 40 Denitrification Methane 20 10 Nitrous oxide 8 Oxygen 10 Excess6 air Unfractionated 15 Carbon monoxide 4 excess air 20 Carbon dioxide 2 0.001 30 Hydrogen 0 10 40 Nitrogen, milligrams per liter Degassing Environmental tracers CFC-11 5 CFC-12 0.0001 CFC-13 0 Henry solubility constant, moles per kilogram atmosphere 0 10 20 30 40 SF6 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 Halon-1301 Temperature, in degrees Celsius Xe to Ne ratio, cubic centimeters per gram of water 2 300 Decay of Tritium > 0.5TU Atmospheric record 1.8 tritium Tritium 0.5TU 1.6 250 Modern 1.4 aged Mantle He 200 Decay of 1.2 tritium 1 10% Mantle + 90% Radiogenic He Air 150 0.8 -air corrected ratio a Mixed 0.6 Radiogenic He 100 /R age s accumulation R 0.4 Pre-modern 50 Apparent aged age 0.2 35 years 0 Chlorofluorocarbon-11, in parts per trillion by volume 0 0.2 0.1 0.1 0.3 0.5 0.7 0.9 1950 1960 1970 1980 1990 2000 2010 2020 He(terr) / (He(s) - He(a)) Apparent Sample date year of recharge 2015 1980 Techniques and Methods 4-F5 U.S. Department of the Interior U.S. Geological Survey Cover Photos: Solubility constant of gases Plot of gases from samples and (in freshwater) included in paths of dissolved gas models. the program. Use of the environmental Analysis of helium isotope tracers for determining age systematics. of the water. DGMETA (Version 1): Dissolved Gas Modeling and Environmental Tracer Analysis Computer Program By Bryant C. Jurgens, J.K. Böhlke, Karl Haase, Eurybiades Busenberg, Andrew G. Hunt, and Jeffrey A. Hansen National Water Quality Assessment Project Techniques and Methods 4-F5 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia: 2020 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Jurgens, B.C., Böhlke, J., Haase, K., Busenberg, E., Hunt, A.G., and Hansen, J.A., 2020, DGMETA (version 1)— Dissolved gas modeling and environmental tracer analysis computer program: U.S. Geological Survey Techniques and Methods 4-F5, 50 p., https://doi.org/ 10.3133/ tm4F5. ISSN 2328-7055 (online) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Methods...........................................................................................................................................................4 Gas Solubilities ......................................................................................................................................4 Approximations for Local Pressure, Water Vapor Pressure, and Salinity .........................5 Forms of Solubility Equations .....................................................................................................6 Pressure Corrections ..................................................................................................................7 Real Gas Corrections ..................................................................................................................8 Unit Conversions ..........................................................................................................................8 Models of Excess Air............................................................................................................................9 Inverse Modeling of Dissolved Gases .............................................................................................10 Monte Carlo Simulations ...................................................................................................................11 Environmental Tracer Calculations ..................................................................................................11 Transient Atmospheric Gases ..................................................................................................12 Tritiogenic Helium-3 and Helium-4 ..........................................................................................12 Program Description �����������������������������������������������������������������������������������������������������������������������������������15 DGMETA Worksheets .........................................................................................................................16 SuppInfo Worksheet ..................................................................................................................16 Database Worksheet .................................................................................................................16 Input_Gases Worksheet ...........................................................................................................19 Input_Tracers Worksheet .........................................................................................................20 DGMETA Operation .............................................................................................................................21 Database .....................................................................................................................................21 Graphing ��������������������������������������������������������������������������������������������������������������������������������������21 Gas Solubilities ..................................................................................................................22 _SolGph Worksheet ..........................................................................................................22 Gas-Gas Graphs ................................................................................................................22 _GasGph Worksheet ........................................................................................................24 Dissolved Gas Modeling ...........................................................................................................25 _ModOut Worksheet ........................................................................................................26 Environmental Tracer Concentrations ....................................................................................27 _TrcOut Worksheet ...........................................................................................................29 Formatting ...................................................................................................................................29 _AvgVal Worksheet ..........................................................................................................29 _ModFlt, _TrcFlt, and _AvgFlt Worksheets ...................................................................29 Examples .......................................................................................................................................................31 Example 1—Comparison of Noble Gas Solubility Data in Freshwater and Seawater ............31 Example 2—Inverse Modeling of Air-Equilibrated Freshwater and Seawater Samples .......34 Example 3—Dissolved Gas Modeling with Neon, Argon, and Nitrogen or Argon and Nitrogen ����������������������������������������������������������������������������������������������������������������������������������35 Example 4—Tritiogenic Helium-3 Analysis in the Central Eastside San Joaquin Valley, California ....................................................................................................................40 Example 5—Degassed Groundwater ..............................................................................................44 iv Installation Notes .........................................................................................................................................45 Disclaimer .....................................................................................................................................................45 References Cited..........................................................................................................................................46 Figures 1. Graphs showing air-water solubility equilibrium concentration of inert noble gases helium, neon, argon, krypton, and xenon in water that are commonly used for modeling air-water equilibrium conditions; air-water solubility equilibrium concentration of the biogeochemically reactive gases nitrogen, oxygen, carbon dioxide, methane,