These data are chemical analyses of discrete samples of groundwater, stream base flow, and springs collected to support a U.S. Geological Survey study to estimate the timing and source of recharge to the basalt groundwater system in the Umatilla River basin, Oregon. Categories of data include: (1) site information (2) field measurements, (3) tracers of groundwater age and source, and (4) dissolved noble gases. These data were collected during August 26, 2014 – September 13, 2022. Data are in .csv file format.

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 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 U.S. Geological Survey (USGS) data release contains stream water chemistry and streamflow data collected in late August and early September, 2021 from 28 sites located throughout Colorado, USA. The sampled streams all drain high-elevation mountain watersheds in areas where the bedrock is hydrothermally altered and contains abundant sulfide minerals. Most sampled streams are therefore affected by natural acid-rock drainage. All sites had been sampled in prior years so that the 2021 data could be used to evaluate potential changes in stream water chemistry in recent decades. Streamflow was also quantified at most sites using data from a sodium chloride slug addition wherein specific conductivity readings were used as a surrogate for the tracer concentration.

This U.S. Geological Survey (USGS) data release contains stream water chemistry and streamflow data collected in late August and early September, 2021 from 28 sites located throughout Colorado, USA. The sampled streams all drain high-elevation mountain watersheds in areas where the bedrock is hydrothermally altered and contains abundant sulfide minerals. Most sampled streams are therefore affected by natural acid-rock drainage. All sites had been sampled in prior years so that the 2021 data could be used to evaluate potential changes in stream water chemistry in recent decades. Streamflow was also quantified at most sites using data from a sodium chloride slug addition wherein specific conductivity readings were used as a surrogate for the tracer concentration.

This data release documents 155 sets of dissolved noble gas analyses (neon, argon, krypton, xenon) and 153 modeled recharge temperatures for groundwater sampled from domestic water supply wells and springs throughout the northern Sierra Nevada foothills as part of the California State Water Resources Control Board’s Groundwater Ambient Monitoring and Assessment (GAMA) Program in 2015-2017. Data from two of the U.S. Geological Survey’s Priority Basin Project Shallow Aquifer Assessment study units are presented here: The Yuba and Bear Watersheds (YB) Shallow Aquifer Study Unit (sampled in 2015-2016) and the Mokelumne, Cosumnes, and American River Watersheds (MCAW) Shallow Aquifer Study Unit (sampled in 2016-2017). The YB and MCAW study units include domestic well and spring sites within watersheds overlying fractured rock aquifer systems of the Sierra Nevada hydrogeologic province of California in Nevada, Yuba, Sierra, Placer, El Dorado, Amador, and Calaveras Counties. Study design and site attributes for the YB and MCAW study units are presented by Jasper and others (2017) and Shelton and others (2018), respectively. This data release contains one tab-delimited text file containing Table 1, which reports the results of dissolved noble gas analyses for environmental samples from 72 sites in the YB study unit in addition to eight field replicates (80 samples total) and environmental samples from 67 sites in the MCAW study unit in addition to eight field replicates (75 samples total). Table 1 also contains groundwater recharge temperatures for 153 samples that were modeled using measured dissolved noble gas concentrations, land surface elevation at the sample site, and sample salinity. Model inputs and outputs including Monte Carlo simulations to estimate model parameter errors are also included in Table 1. Detailed descriptions for Table 1 column fields are provided in an additional tab-delimited text file of Table 1 column definitions. Abbreviations used in this data release are explained in an additional tab-delimited text file of abbreviations. These data support the following publications: Jasper, M., Bennett, G.L., and Fram, M.S., 2017, Groundwater-Quality Data in the Yuba and Bear Watersheds Shallow Aquifer Study Unit, 2015-2016: Results from the California GAMA Priority Basin Project: U.S. Geological Survey data release, https://doi.org/10.5066/F73F4MS9. Levy, Z.F., Fram, M.S., Faulkner, K.E., Alpers, C.N., Soltero, E.M., and Taylor, K.A., 2020, Effects of montane watershed development on vulnerability of domestic groundwater supply during drought: Journal of Hydrology, v. 583, https://doi.org/10.1016/j.jhydrol.2020.124567. Shelton, J.L., Fram, M.S., Goldrath, D.A., Bennett, G.L., V, and Jasper, M., 2018, Groundwater-quality data in the Mokelumne, Cosumnes, and American River Watersheds Shallow Aquifer Study Unit, 2016-2017: Results from the California GAMA Priority Basin Project: U.S. Geological Survey data release, https://doi.org/10.5066/F78G8JXP.

The U.S. Geological Survey (USGS) National Extent Hydrogeologic Framework for National Water Census (NEHF) project is a multi-year effort (2022 through 2025) that will compile existing assets (approaches, data, software, etc.), develop a strategic plan, and implement an operational framework that is dynamic and multi-scale. Within the USGS, numerical groundwater-flow and solute- and heat-transport models have been created for a variety of purposes that include water-resource assessments, contaminant-transport evaluations, and water-management planning. These models are often supported by hydrogeologic-framework studies that describe the surface and subsurface distribution of geologic materials and their hydrologic properties. This digital data release was developed as part of the NEHF project to compile, in tabular and spatial form, information on the salient characteristics of numerical groundwater-flow and solute- and heat-transport models published or developed by the USGS for regions in the U.S. and its territories and commonwealths from the date of the earliest published model, 1970, through 2022. Version 2.0 of this data release adds spatial information on the structural and hydrologic properties of a subset of the models. First release: September 2024 (available from author) Revised: March 2025 (ver. 2.0)

Brackish groundwater (BGW), defined for this assessment as having a dissolved-solids concentration between 1,000 and 10,000 milligrams per liter is an unconventional source of water that may offer a partial solution to current (2016) and future water challenges. In support of the National Water Census, the U.S. Geological Survey has completed a BGW assessment to gain a better understanding of the occurrence and character of BGW resources of the United States as an alternative source of water. Analyses completed as part of this assessment relied on previously collected data from multiple sources, and no new data were collected. One of the most important contributions of this assessment is the creation of a database containing chemical data and aquifer information for the known quantities of BGW in the United States. Data were compiled from single publications to large datasets and from local studies to national assessments, and includes chemical data on the concentrations of dissolved solids, major ions, trace elements, nutrients, radionuclides, and physical properties of the resource (pH, temperature, specific conductance). This dataset represents major-ions data from a compilation of water-quality samples from 33 sources for almost 384,000 groundwater wells across the continental U.S., Alaska, Hawaii, Puerto Rico, the U.S. Virgin Islands, Guam, and American Samoa. The data are published here as an ESRI geodatabase with a point feature class, and associated attribute table, and also as non-proprietary comma-separated value table. Dissolved-solids data include information for assessing the distribution of dissolved-solids concentrations and other chemical constituents that may limit the usability of brackish groundwater. It was not possible to compile all data available for the Nation, and data selected for this investigation were mostly limited to larger datasets that were available in a digital format. As a result, some data on a more local-scale may not be included.

This dataset contains measurements of dissolved hydrocarbons in from various water sources, as well as ancillary raw calibration data showing the stability of the gas chromatograph with an atomic emission detector and flame ionization detector (GC-AED-FID) analytical system over time. Across multiple studies, samples from tap water, groundwater, surface water, springs, mine outflows, and blank materials were analyzed using this system over a period from 2014 to 2017, comprising 172 samples analyzed. In addition to water samples, 183 calibrations conducted over the same period of time are included to document the stability of the GC-AED-FID system over time. The target analytes in this study were: methane (CH4), ethane (C2H6), ethene (C2H4), ethyne (C2H2), propane (C3H8), propene (C3H6), i-butane (C4H10), n-butane (C4H10), 1-butene (C4H8), propyne (C3H4), i-pentane (C5H12), n-pentane (C5H12), 2-methyl-pentane (C6H14), 3-methyl-pentane (C6H14), hexane (C6H14), and benzene (C6H6).

Groundwater chemistry data used for assessing the lead (Pb) solubility potential of untreated groundwater of the United States were compiled from the USGS National Water Information System (NWIS) database for groundwater sites sampled between January 1, 2000 and January 1, 2016. Two datasets were compiled: one dataset having 13,324 groundwater sites was used to assess Pb occurrence in untreated groundwater from different well types and a second dataset having 8,313 groundwater sites was used for geochemical modeling (Tables S1 and S2). In both datasets, only the most recent sample was used when multiple water-quality samples were available for a site. Samples were collected in accordance with protocols established by the USGS National Field Manual and the USGS National Water Quality Assessment (NAWQA) project. Samples for Pb, major ions, and nutrients were filtered with 0.45 µm capsule filters prior to analysis. Pb was screened to a common reporting level of 1 µg/L. Non-detections and detected Pb concentrations that were at or below 1 µg/L were recoded to 0.5 µg/L. Non-detections of Pb above 1 µg/L were removed from the dataset. The censoring of reporting levels mainly affected older samples that used analytical methods with higher detection levels. Table 1 includes groundwater samples from sites used for public-supply (PS), domestic (DOM), monitoring, and for other purposes, such as irrigation, stock, or industrial supply. Groundwater sites are mainly wells, but include some springs. From heretofore drinking water supply (DW) sites will be used to refer to DOM and PS sites as a group. The geochemical modeling dataset was compiled to obtain DW samples with a complete set of measured values of pH, calcium, magnesium, sodium, chloride, and sulfate. Alkalinity, fluoride (F), orthophosphate (OP), and bromide were included when available. DW sites were the primary source of data used to evaluate the solubility of Pb in untreated groundwater. Pb that was measured on the same date as the sample used for geochemical modeling was retained for statistical analysis of model output but was not included as input to the geochemical model. In addition, samples with missing alkalinity values were included when pH was at or below 5.5 and cation-anion balances were within 5%, indicating alkalinity was not a major component of the ion chemistry.