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.

Groundwater age distributions and susceptibility to natural and anthropogenic contaminants were assessed for selected wells across Minnesota. The data provide information to understand how long it will take to observe groundwater quality improvements from best management practices implemented at land surface to reduce losses of nitrate (and other chemicals) from agricultural practices. A total of 13 age estimates were done on samples collected from 8 wells between July 1996 and May 1997. Groundwater ages were estimated from dissolved gas (argon and nitrogen) and environmental tracer data (tritium, chlorofluorocarbons, and tritiogenic helium-3) from field samples using the equations available in TracerLPM (an Excel® workbook for interpreting groundwater age distributions from environmental tracer data) and DGMETA (an Excel® workbook for dissolved gas modeling and environmental tracer analysis); groundwater age estimates are reported in Table_1_Age_Information.txt. DGMETA was used to compute optimal water temperature and excess air that explain the measured dissolved gases (argon and nitrogen) in a sample; condensed results are reported in Table_1_Age_Information.txt and these results are reported in detail in Table_2_Dissolved_Gases.txt. These values were then used to convert the raw measured concentrations of chlorofluorocarbons into a form appropriate for age dating analysis, the dry air mixing ratio of chlorofluorocarbons; these results are reported in Table_3_Computed_Tracer_Concentrations.txt. Table_4_Additional_Helium.txt reports calculated concentrations of tritiogenic helium that were used in groundwater age calculations and the measured concentrations used in those calculations. Table_5_Site_And_Background_Information.txt reports additional site information and field parameters. In addition to these five tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-5. A readme file is provided that describes each table in more detail and processes to use the data in this data release to view age distributions in TracerLPM and to set up TracerLPM to run scenarios for other chemicals of interest.

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)).

Groundwater age distributions and susceptibility to natural and anthropogenic contaminants were assessed for selected wells, streambed piezometers, and springs in southeastern Minnesota. The data provide information to understand how long it will take to observe groundwater quality improvements from best management practices implemented at land surface to reduce losses of nitrate (and other chemicals) from agricultural practices. Nineteen water samples were collected from ten wells, three streambed piezometers, and four springs between August 2020 and September 2022. Two of these samples are field replicate samples collected from a spring site and a well site. A child item contains historical data from 15 water samples from 10 wells between July 1996 to May 1997. Groundwater ages were estimated from dissolved gas (neon, argon, krypton, and xenon) and environmental tracer data (tritium, sulfur hexafluoride, chlorofluorocarbons, and tritiogenic helium-3) from field samples using the equations available in TracerLPM (an Excel® workbook for interpreting groundwater age distributions from environmental tracer data) and DGMETA (an Excel® workbook for dissolved gas modeling and environmental tracer analysis); groundwater age estimates are reported in Table_1_Age_Information.txt. DGMETA was used to compute the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) for the measured dissolved gases in a sample; condensed results are reported in Table_1_Age_Information.txt and these results are reported in detail in Table_2_Dissolved_Gases.txt. These values were then used to convert the raw measured concentrations of environmental tracers into a form appropriate for age dating analysis; these results are reported in Table_3_Computed_Tracer_Concentrations.txt. Calculated concentrations of environmental tracers that were used in groundwater age calculations are the dry air mixing ratio of sulfur hexafluoride or chlorofluorocarbons, and tritiogenic helium-3, which is the concentration of helium-3 from the decay of tritium. Table_4_Site_And_Background_Information.txt reports additional site information and field parameters. In addition to these four tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-4. A readme file is provided that describes each table in more detail and processes to use the data in this data release to view age distributions in TracerLPM and to set up TracerLPM to run scenarios for other chemicals of interest.

Groundwater age distributions and susceptibility to natural and anthropogenic contaminants were assessed for selected wells, streambed piezometers, and springs in southeastern Minnesota. The data provide information to understand how long it will take to observe groundwater quality improvements from best management practices implemented at land surface to reduce losses of nitrate (and other chemicals) from agricultural practices. Nineteen water samples were collected from ten wells, three streambed piezometers, and four springs between August 2020 and September 2022. Two of these samples are field replicate samples collected from a spring site and a well site. A child item contains historical data from 15 water samples from 10 wells between July 1996 to May 1997. Groundwater ages were estimated from dissolved gas (neon, argon, krypton, and xenon) and environmental tracer data (tritium, sulfur hexafluoride, chlorofluorocarbons, and tritiogenic helium-3) from field samples using the equations available in TracerLPM (an Excel® workbook for interpreting groundwater age distributions from environmental tracer data) and DGMETA (an Excel® workbook for dissolved gas modeling and environmental tracer analysis); groundwater age estimates are reported in Table_1_Age_Information.txt. DGMETA was used to compute the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) for the measured dissolved gases in a sample; condensed results are reported in Table_1_Age_Information.txt and these results are reported in detail in Table_2_Dissolved_Gases.txt. These values were then used to convert the raw measured concentrations of environmental tracers into a form appropriate for age dating analysis; these results are reported in Table_3_Computed_Tracer_Concentrations.txt. Calculated concentrations of environmental tracers that were used in groundwater age calculations are the dry air mixing ratio of sulfur hexafluoride or chlorofluorocarbons, and tritiogenic helium-3, which is the concentration of helium-3 from the decay of tritium. Table_4_Site_And_Background_Information.txt reports additional site information and field parameters. In addition to these four tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-4. A readme file is provided that describes each table in more detail and processes to use the data in this data release to view age distributions in TracerLPM and to set up TracerLPM to run scenarios for other chemicals of interest.

Five MODFLOW-NWT inset models were extracted from the Lake Michigan Basin (LMB) regional model (https://pubs.usgs.gov/sir/2010/5109/). These inset models were designed to serve as a training ground for metamodels of groundwater age in glacial wells. The study areas of the inset models correspond to HUC8 basins. Two of the basins are tributary to Lake Michigan from the east, two are tributary to the lake from the west, and one is located outside the western boundary of the Lake Michigan topographic basin. The inset models inherit many of the inputs to the parent LMB model, such as its hydrostratigraphy and layering scheme, the hydraulic conductivity assigned bedrock layers, the recharge distribution, and water use in the form of pumping rates from glacial and bedrock wells. The construction of the inset models entails modifying some inputs, most notably the grid spacing (reduced from cells 5000-ft on a side in the parent model to 500-ft on a side in the inset models). The refined grid spacing allowed more precise location of pumping wells and more detailed simulation of groundwater/surface-water interactions. Also modified are the glacial hydraulic conductivity values, the top bedrock surface elevation, and the surface-water network input to the inset models. The inset models are solved using the MODFLOW-NWT code which allows for more robust handling of conditions in unconfined aquifers than previous versions of MODFLOW. The particle-tracking code MODPATH was used to simulate the distribution of age of groundwater discharging to wells pumping from glacial deposits. This USGS data release contains all of the input and output files for the simulation of the inset models of the Lake Michigan Basins model as described in the associated model documentation report (https://doi.org/10.3133/sir20185038).

This data set contains 2,611 water levels collected by Natural Resources Districts in Central Nebraska. These water levels were collected by the districts to monitor groundwater levels within the districts. The water levels were provided to the USGS for use as calibration targets to the Elkhorn and Loup River Basin - Phase Three groundwater flow model. The water levels have not been previously published. This record serves as the publication record of the water levels in support of the Elkhorn and Loup River Basin - Phase Three groundwater flow model report.

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 groundwater-flow model archive/data release contains the model input and output files for 1) edited versions of four of the five NAWQA steady- state, inset MODFLOW-NWT models of regional model of Lake Michigan Basin (https://doi.org/10.3133/sir20185038) and 2) general models simulating the same four basins as the four inset models. Two HUC8 basins in the lower peninsula of Michigan (Kalamazoo (KALA) and Boardman-Charlevoix (BOARD) basins) and two HUC8 basins in Wisconsin (Upper Fox (UFOX) and Manitowoc-Sheboygan (MANI) basins) are represented in the inset and genera-simulation models. The inset models are designed to serve as a training area for metamodels to estimate groundwater age in glacial wells. The construction and details of the original four inset models are outlined in the U.S. Geological Survey Scientific Investigations Report 2018-5038 (https://doi.org/10.3133/sir20185038), and the construction and details of the general models are outlined in the Water Resources Research journal article (https://doi.org/10.1029/2017WR021531). The original four inset models are archived in the data release at https://doi.org/10.5066/F76D5R5V. Groundwater withdrawals from wells in the original four inset models were removed in the inset models in this archive because the general models did not have wells and to be able to compare the results from the two types of models in the archive. The boundary conditions of these “pre-development” versions of the inset models were changed from constant-head boundaries (reflecting 2005 conditions) to no-flow boundaries. The general-simulation models apply an innovative modeling approach that allows for rapid,automated construction and calibration of models at a scale appropriate to the problem at hand (https://doi.org/10.3133/sir20215142). Results from the four general models in this archive were compared to results from the edited versions of the four inset models to evaluate the degree to which the general models reproduce behavior simulated by the inset models that use conventional flow modeling techniques. The underlying directories contain all the input and output files for the MODFLOW-NWT simulations and MODPATH particle tracking analysis for the edited versions of four inset models, and the four general models simulating the same four basins as the inset models described in the USGS Scientific Investigations Report (https://doi.org/10.3133sir20215142). The MODFLOW-NWT (v 1.0.9) and MODPATH 6 (version 6.0.1) executables and source codes, various ancillary python scripts written for this project, and model geospatial data are also included in the archive. Descriptions of the data in each subdirectory are provided to facilitate understanding of this this model archive. File descriptions are provided for select input and output files to provide additional information that may be of use for understanding this this model archive.

This data release documents four Microsoft Excel tables; one contains data for understanding water ages, one contains noble gas model data, two that describe the data fields. Results described include environmental tracer concentrations (tritium, tritiogenic helium-3, choloroflourocarbons, and radiogenic helium-4), mean age and age distribution, noble gas concentrations, and groundwater recharge conditions. Mean age and age distribution results (LPM) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). Please see the main manuscript for additional details on the results presented in this table. Noble gas model results (CEmodel) contain noble gas concentrations and closed-equilibrium model results. Please see the main manuscript for additional details on the results presented in this table.