This data release documents two Microsoft Excel tables that contain data for understanding tracer concentrations and groundwater age in the Columbia Plateau aquifer system. Results for geochemical correction of carbon-14, and lumped parameter modeling of groundwater age for the sample network (VPFS, vertical flow path study) are described. Geochemical carbon-14 correction results (RFG) describe geochemical correction of carbon-14 in dissolved inorganic carbon (DIC) for groundwater age dating. Datasets includes measured water parameters and chemistry, model parameter inputs, and final corrected carbon-14 in DIC. Geochemical correction was completed using the revised Fontes and Granier model of Han and Plummer (2013). Mean age and age distribution results (TracerLPM) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). Please see the processing steps below for additional details on the results presented in this table.

This data release describes one (1) Microsoft Excel table of lumped parameter models of groundwater age for groundwater discharging to the South Loup River, Nebraska. The table (LPMAgeResults) includes final models of groundwater age and metrics by calibration of lumped parameter models to tracer concentrations using TracerLPM software (Jurgens and others, 2012). Interpreted results presented here were used to guide hydrologic interpretations of groundwater sources and flow paths of groundwater discharging to the South Loup River, NE.

This data release describes one (1) Microsoft Excel table of lumped parameter models of groundwater age for groundwater discharging to the South Loup River, Nebraska. The table (LPMAgeResults) includes final models of groundwater age and metrics by calibration of lumped parameter models to tracer concentrations using TracerLPM software (Jurgens and others, 2012). Interpreted results presented here were used to guide hydrologic interpretations of groundwater sources and flow paths of groundwater discharging to the South Loup River, NE.

This data release documents two Microsoft Excel tables; one contains data for understanding groundwater ages in the Spanish Valley watershed, and one that describe the data fields. Mean ages and age distributions from 19 groundwater samples were estimated in support of an evaluation of the groundwater resources of the Spanish Valley watershed (Masbruch and others, 2019). Individual groundwater well and spring vulnerability to land-surface contamination and changes in hydraulic conditions (for example, water extraction or reduced recharge) can be assessed using environmental tracer-based groundwater age. The detailed interpretation of groundwater age reported here supplements the apparent tracer ages of Masbruch and others (2019). Multiple age tracers sampled in groundwater were fit using TracerLPM (Jurgens and others, 2012), with working knowledge of the well dimensions, hydrogeology, and geochemistry, to assign a unique age distribution. The age distributions describes the relative contributions of flow-paths of differing age and the extent of flow-path mixing in the sample. Concentrations of tritium (3H), tritiogenic-He (3Hetrit), chlorofluorocarbons (CFC-11, -12, -113), sulphur hexafloride (SF6), and geochemically corrected carbon-14 (14C) were fit by optimizing age distribution parameters. Details of 3Hetrit calculation, 14C geochemical correction, and noble gas based estimates of conditions which were used to correct CFCs and SF6 are described in Masbruch and others (2019). Lumped parameter models (LPM) are described for each sample by the mean age, LPM name, model parameters, and in the the case of binary mixing models (BMM) the mixing fraction and the mean age of the old component. Final mean age for BMMs is calculated as (Mean Age 1 * Fraction) + (Mean Age 2 * (1 – Fraction)).

This data release documents two Microsoft Excel tables; one contains data for understanding groundwater ages in the Spanish Valley watershed, and one that describe the data fields. Mean ages and age distributions from 19 groundwater samples were estimated in support of an evaluation of the groundwater resources of the Spanish Valley watershed (Masbruch and others, 2019). Individual groundwater well and spring vulnerability to land-surface contamination and changes in hydraulic conditions (for example, water extraction or reduced recharge) can be assessed using environmental tracer-based groundwater age. The detailed interpretation of groundwater age reported here supplements the apparent tracer ages of Masbruch and others (2019). Multiple age tracers sampled in groundwater were fit using TracerLPM (Jurgens and others, 2012), with working knowledge of the well dimensions, hydrogeology, and geochemistry, to assign a unique age distribution. The age distributions describes the relative contributions of flow-paths of differing age and the extent of flow-path mixing in the sample. Concentrations of tritium (3H), tritiogenic-He (3Hetrit), chlorofluorocarbons (CFC-11, -12, -113), sulphur hexafloride (SF6), and geochemically corrected carbon-14 (14C) were fit by optimizing age distribution parameters. Details of 3Hetrit calculation, 14C geochemical correction, and noble gas based estimates of conditions which were used to correct CFCs and SF6 are described in Masbruch and others (2019). Lumped parameter models (LPM) are described for each sample by the mean age, LPM name, model parameters, and in the the case of binary mixing models (BMM) the mixing fraction and the mean age of the old component. Final mean age for BMMs is calculated as (Mean Age 1 * Fraction) + (Mean Age 2 * (1 – Fraction)).

This data release documents nine Microsoft Excel tables that contain data for understanding groundwater ages in the Glacial aquifer system. Results for the four sample networks (PAS, principal aquifer study; MSS, modeling support study; FPS, flow path study) are described by three tables each: dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14, and radiogenic helium-4), and results for the mean age and age distribution. Tables are labeled by network and data type (as described below) separated by an underscore (_). For example, dissolved gas modeling results from the PAS network is label ‘PAS_NGmodel’. Dissolved gas modeling results (NGmodel) contains detailed information on the calibration of dissolved gas models to dissolved gas concentrations (neon, argon, krypton, xenon, and nitrogen). Calibration was done using methods described by Aeschbach-Hertig and others (1999) with modifications to include nitrogen gas (Weiss 1970). In most cases, a single set of noble gas data (neon, argon, krypton, and xenon) were used to determine recharge conditions (recharge temperature, excess air or entrapped air, fractionation). In cases where noble gas data were not available, multiple analyses of nitrogen and argon (collected sequentially on the same sample date) were used to determine recharge conditions. Environmental tracer results (Tracers) contain detailed information on calculations of environmental tracer data. Dissolved gas models were paired with sulfur hexafluoride and helium isotopes (3He/4He) and helium to determine concentrations of tritiogenic helium-3 (from decay of tritium; Solomon and Cook, 2000) and radiogenic helium-4 (from decay of uranium and thorium in aquifer materials; Solomon, 2000). Multiple tracer concentrations were computed when sites had multiple dissolved gas model results and analyses for sulfur hexafluoride or helium isotopes. Mean age and age distribution results (LPMModOut) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). One additional table describes LPM results from a previous sampling of the FPS network in 2004. Tracer concentrations from 2004 FPS sampling are described in previous publication (Tesoriero et al., 2007; Saad, 2008). Dissolved gas modeling and environmental tracer results were averaged when multiple dissolved gas models and tracer concentrations were computed. In cases where age was modeled with a binary lumped parameter model (BMM), the mean age was computed from the mean age and fraction of the two components in the mixture. Please see the processing steps below and the main manuscript for additional details on the results presented in this table.

This data release documents nine Microsoft Excel tables that contain data for understanding groundwater ages in the Glacial aquifer system. Results for the four sample networks (PAS, principal aquifer study; MSS, modeling support study; FPS, flow path study) are described by three tables each: dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14, and radiogenic helium-4), and results for the mean age and age distribution. Tables are labeled by network and data type (as described below) separated by an underscore (_). For example, dissolved gas modeling results from the PAS network is label ‘PAS_NGmodel’. Dissolved gas modeling results (NGmodel) contains detailed information on the calibration of dissolved gas models to dissolved gas concentrations (neon, argon, krypton, xenon, and nitrogen). Calibration was done using methods described by Aeschbach-Hertig and others (1999) with modifications to include nitrogen gas (Weiss 1970). In most cases, a single set of noble gas data (neon, argon, krypton, and xenon) were used to determine recharge conditions (recharge temperature, excess air or entrapped air, fractionation). In cases where noble gas data were not available, multiple analyses of nitrogen and argon (collected sequentially on the same sample date) were used to determine recharge conditions. Environmental tracer results (Tracers) contain detailed information on calculations of environmental tracer data. Dissolved gas models were paired with sulfur hexafluoride and helium isotopes (3He/4He) and helium to determine concentrations of tritiogenic helium-3 (from decay of tritium; Solomon and Cook, 2000) and radiogenic helium-4 (from decay of uranium and thorium in aquifer materials; Solomon, 2000). Multiple tracer concentrations were computed when sites had multiple dissolved gas model results and analyses for sulfur hexafluoride or helium isotopes. Mean age and age distribution results (LPMModOut) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). One additional table describes LPM results from a previous sampling of the FPS network in 2004. Tracer concentrations from 2004 FPS sampling are described in previous publication (Tesoriero et al., 2007; Saad, 2008). Dissolved gas modeling and environmental tracer results were averaged when multiple dissolved gas models and tracer concentrations were computed. In cases where age was modeled with a binary lumped parameter model (BMM), the mean age was computed from the mean age and fraction of the two components in the mixture. Please see the processing steps below and the main manuscript for additional details on the results presented in this table.

This data release documents three Microsoft Excel tables that contain data for understanding environmental tracer concentrations in groundwater of the Columbia Plateau aquifer system. Results of dissolved-gas modeling using environmental tracer concentrations (tritium, tritiogenic helium-3, and radiogenic helium-4), for the sample network (VPFS, vertical flow path study) are described. Dissolved gas modeling results (ModOut) contains detailed information on the calibration of dissolved gas models to measured dissolved-gas concentrations (neon, argon, krypton, xenon, and nitrogen). Calibration was done using methods described by Aeschbach-Hertig and others (1999 & 2000) with modifications to include nitrogen gas (Weiss, 1970). In most cases, a single set of noble-gas concentrations (neon, argon, krypton, and xenon) was used to solve for recharge conditions (recharge temperature, excess or entrapped air, and fractionation) using the unfractionated excess air (UA) and closed equilibration (CE) models (Aeschbach-Hertig and others, 1999 & 2000). In cases where noble gas data were not available, multiple analyses of nitrogen and argon (collected sequentially on the same sample date) were used to solve for recharge conditions. Environmental tracer results (TrcOut) contains detailed information on calculations of environmental tracer data. Dissolved gas models were paired with measured helium isotope ratios (3He/4He) and helium concentrations to calculate concentrations of tritiogenic helium-3 (the component of 3He derived from tritium decay; Solomon and Cook, 2000) and radiogenic helium-4 (the component of 4He derived from the decay of uranium and thorium in aquifer materials; Solomon, 2000). Tracer concentrations were computed for each combination of measure dissolved gas concentrations when sites had multiple measured gas results and analyses for helium isotopes. Average environmental tracer results (AvgTrcOut) contains average tracer concentrations for a given site used for determination of groundwater ages. Aeschbach-Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer (1999), Interpretation of dissolved atmospheric noble gases in natural waters, Water Resour. Res., 35(9), 2779–2792,https://dx.doi.org/10.1029/1999WR900130. Aeschbach-Hertig, W., F. Peeters, U. Beyerle, and R. Kipfer (2000), Paleotemperature reconstruction from noble gases in ground water taking into account equilibration with entrapped air, Nature, v. 405, Iss. 6790, pg. 1040-1044, http://dx.doi.org/10.1038/35016542 Solomon, D.K., and P.G. Cook. 2000. 3H and 3He. In Environmental Tracers in Subsurface Hydrology, ed. P.G. Cook and A.L. Herczeg, 197-424. Boston: Kluwer Academic Publishers. Solomon, D.K. 2000. 4He in groundwater. In Environmental Tracers in Subsurface Hydrology, ed. P.G. Cook and A.L. Herczeg, 425-439. Boston: Kluwer Academic Publishers. Weiss, R. F., 1970, The solubility of nitrogen, oxygen, and argon in water and seawater, Deep Sea Research, vol. 17, pp. 721-735, https://doi.org/10.1016/0011-7471(70)90037-9.

This data release documents eight Microsoft Excel tables; four which contain data for understanding groundwater ages in the South East Coastal Plain (SECP), Coastal Lowlands (CLOW) and Mississippi Embayment and Texas Coastal Uplands (METX) aquifer systems and four that describe the data fields. Results described include dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, and radiogenic helium-4), mean age and age distribution, and carbon-14 geochemical model input and results. Dissolved gas modeling results (DGmodel) contains detailed information on the calibration of dissolved gas models to dissolved gas concentrations (neon, argon, krypton, xenon, and nitrogen). Calibration was done using methods described by Aeschbach-Hertig and others (1999) with modifications to include nitrogen gas (Weiss 1970). In most cases, a single set of noble gas data (neon, argon, krypton, and xenon) were used to determine recharge conditions (recharge temperature, excess air or entrapped air, fractionation). In cases where noble gas data were not available, multiple analyses of nitrogen and argon (collected sequentially on the same sample date) were used to determine recharge conditions. Environmental tracer results (Tracers) contain detailed information on calculations of environmental tracer data. Dissolved gas models were paired with sulfur hexafluoride and helium isotopes (3He/4He) and helium to determine concentrations of tritiogenic helium-3 (from decay of tritium; Solomon and Cook, 2000) and radiogenic helium-4 (from decay of uranium and thorium in aquifer materials; Solomon, 2000). Multiple tracer concentrations were computed when sites had multiple dissolved gas model results and analyses for sulfur hexafluoride or helium isotopes. Mean age and age distribution results (TracerLPM) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). In cases where age was modeled with a binary lumped parameter model (BMM), the mean age was computed from the mean age and fraction of the two components in the mixture. Additional results for select sites, identified with a “-1” or “-2” suffix to USGS Station ID, detail the estimated range corrected 14C activity and groundwater mean age as a result of uncertainty in 14C geochemical correction. Please see the processing steps below and the main manuscript for additional details on the results presented in this table. Carbon-14 geochemical model results (Carbon14) contain model inputs and final adjusted carbon-14 input to TracerLPM for determination of groundwater age.Carbon-14 adjustments were made using the revised Fontes and Garnier model (Han and Plummer, 2013).

This data release documents eight Microsoft Excel tables; four which contain data for understanding groundwater ages in the South East Coastal Plain (SECP), Coastal Lowlands (CLOW) and Mississippi Embayment and Texas Coastal Uplands (METX) aquifer systems and four that describe the data fields. Results described include dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, and radiogenic helium-4), mean age and age distribution, and carbon-14 geochemical model input and results. Dissolved gas modeling results (DGmodel) contains detailed information on the calibration of dissolved gas models to dissolved gas concentrations (neon, argon, krypton, xenon, and nitrogen). Calibration was done using methods described by Aeschbach-Hertig and others (1999) with modifications to include nitrogen gas (Weiss 1970). In most cases, a single set of noble gas data (neon, argon, krypton, and xenon) were used to determine recharge conditions (recharge temperature, excess air or entrapped air, fractionation). In cases where noble gas data were not available, multiple analyses of nitrogen and argon (collected sequentially on the same sample date) were used to determine recharge conditions. Environmental tracer results (Tracers) contain detailed information on calculations of environmental tracer data. Dissolved gas models were paired with sulfur hexafluoride and helium isotopes (3He/4He) and helium to determine concentrations of tritiogenic helium-3 (from decay of tritium; Solomon and Cook, 2000) and radiogenic helium-4 (from decay of uranium and thorium in aquifer materials; Solomon, 2000). Multiple tracer concentrations were computed when sites had multiple dissolved gas model results and analyses for sulfur hexafluoride or helium isotopes. Mean age and age distribution results (TracerLPM) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). In cases where age was modeled with a binary lumped parameter model (BMM), the mean age was computed from the mean age and fraction of the two components in the mixture. Additional results for select sites, identified with a “-1” or “-2” suffix to USGS Station ID, detail the estimated range corrected 14C activity and groundwater mean age as a result of uncertainty in 14C geochemical correction. Please see the processing steps below and the main manuscript for additional details on the results presented in this table. Carbon-14 geochemical model results (Carbon14) contain model inputs and final adjusted carbon-14 input to TracerLPM for determination of groundwater age.Carbon-14 adjustments were made using the revised Fontes and Garnier model (Han and Plummer, 2013).