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.

Groundwater age distribution and susceptibility to natural and anthropogenic contaminants were assessed for selected principal aquifers of the Western United States: the Central Valley aquifer system (CVAL), the Basin and Range basin-fill aquifers (BNRF), the Rio Grande aquifer system (RIOG), the High Plains aquifer (HPAQ), the Columbia Plateau basaltic-rock aquifers (CLPT), and the Colorado Plateaus aquifers (COPL). Groundwater ages were estimated by calibration of environmental tracers (tritium, tritiogenic helium-3, chlorofluorocarbons, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models (LPMs) for 1,353 samples from 1,182 sample locations. Groundwater samples were collected from wells (mainly drinking-water) in the CVAL between 2004 and 2018 as part of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP) and the National Water-Quality Assessment (NAWQA) Project; and in the BNRF in 2013, the RIOG in 2014 and 2015, the HPAQ between 2014 and 2017, the CPLT in 2016, and the COPL in 2017 as part of NAWQA. Table 1 reports the primary results of this assessment and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations; results of the tritium age classification, susceptibility index, and mean groundwater age of each sample in this assessment; and water level and well construction information for some wells. Calibrated lumped parameter models provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages that explain the measured tracer concentrations in a sample. Tables 2 and 3 provide results in support of Table 1. Table 2 reports detailed results for the calibration of dissolved gas models to neon, argon, krypton, xenon, and nitrogen. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) that explain the measured dissolved gases in a sample. Table 3 reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results in Table 2. Calculated concentrations of environmental tracers that can be used in groundwater age calculations are the dry air mixing ratio of sulfur hexafluoride or chlorofluorocarbons, tritiogenic helium-3, which is the concentration of helium-3 from the decay of tritium, and radiogenic helium-4, which is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. In addition to these three tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-3.

Groundwater age distribution and susceptibility to natural and anthropogenic contaminants were assessed for selected principal aquifers of the Western United States: the Central Valley aquifer system (CVAL), the Basin and Range basin-fill aquifers (BNRF), the Rio Grande aquifer system (RIOG), the High Plains aquifer (HPAQ), the Columbia Plateau basaltic-rock aquifers (CLPT), and the Colorado Plateaus aquifers (COPL). Groundwater ages were estimated by calibration of environmental tracers (tritium, tritiogenic helium-3, chlorofluorocarbons, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models (LPMs) for 1,353 samples from 1,182 sample locations. Groundwater samples were collected from wells (mainly drinking-water) in the CVAL between 2004 and 2018 as part of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP) and the National Water-Quality Assessment (NAWQA) Project; and in the BNRF in 2013, the RIOG in 2014 and 2015, the HPAQ between 2014 and 2017, the CPLT in 2016, and the COPL in 2017 as part of NAWQA. Table 1 reports the primary results of this assessment and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations; results of the tritium age classification, susceptibility index, and mean groundwater age of each sample in this assessment; and water level and well construction information for some wells. Calibrated lumped parameter models provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages that explain the measured tracer concentrations in a sample. Tables 2 and 3 provide results in support of Table 1. Table 2 reports detailed results for the calibration of dissolved gas models to neon, argon, krypton, xenon, and nitrogen. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) that explain the measured dissolved gases in a sample. Table 3 reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results in Table 2. Calculated concentrations of environmental tracers that can be used in groundwater age calculations are the dry air mixing ratio of sulfur hexafluoride or chlorofluorocarbons, tritiogenic helium-3, which is the concentration of helium-3 from the decay of tritium, and radiogenic helium-4, which is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. In addition to these three tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-3.

This data release includes grids representing the depth and thickness of drinking-water withdrawal zones, polygons of hydrogeologic settings, an inventory of sources of well construction data, and summaries of data comparisons used to assess the depth of groundwater used for drinking-water supplies in the United States. Well construction data sources are documented in Table1_DataSources.xlsx. Data comparisons using the Mann-Whitney test to assess similarity between hydrogeologic settings were used to justify combining data where they were sparse (compare_neighbors_all_domestic.txt and compare_neighbors_all_public.txt). Water-supply-well depth varies geographically by water use and the type of well, which illustrates the need to identify the depth of domestic drinking water withdrawal and depth of public supply drinking water withdrawal zones. Water-supply-well depth also varies by aquifer; therefore median values were calculated for each Principal Aquifer (PA), Secondary Hydrogeologic Region (SHR) between PAs and PA or SHR associated with overlying sediment polygons, where present, including glacial (G), coarse glacial (GC), and stream-valley alluvium (AV) polygons (all termed hydrogeologic settings here). A polygon shape file of hydrogeologic settings is included in this data release (HG_Settings.zip) and includes well counts and median thicknesses and depths for each area. This data release documents an inventory of well construction data sources and thickness and median top and bottom of drinking water depth zones by aquifer for domestic and public supplies. This data release includes equations used for estimating information for wells missing information on the depth to the top/length of the open interval. This data release contains: HG_Settings.zip --Shape file with well counts and median depth and thickness for hydrogeologic setting areas compare_neighbors_all_domestic.txt --results of Mann-Whitney tests to assess domestic-supply well construction data similarity between hydrogeologic settings compare_neighbors_all_public.txt --results of Mann-Whitney tests to assess public-supply well construction data similarity between hydrogeologic settings Depth_of_Drinking_Water_Supplies_Metadata03162021.xml --Metadata NonReferencedDomestic.txt --An inventory of domestic-supply well data that are not published elsewhere NonReferencedPublic.txt --An inventory of public-supply well data that are not published elsewhere Table1_DataSources.xlsx --An inventory of databases, references, state web sites, and individual state contacts for data sources. The logic behind data extraction algorithms is also defined for each data source. A tab delimited text version with the same name is also available. Lithology_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by lithology, overlying sediment, and well type HydrogeologicSetting_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by hydrogeologic setting and well type domestic_grids.zip contains: domestic_bottom_dist_to_5.asc --Grid of domestic-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval domestic_open_dist_to_5.asc --Grid of domestic-supply well open interval length data density, distance to reach 5 wells with information on open interval length domestic_bottom_open.asc --Grid of domestic-supply well depth to the bottom of the open interval domestic_len_open.asc --Grid of domestic-supply well open-interval length domestic_top_open.asc --Grid of domestic-supply well depth to the top of the open interval public_grids.zip contains: public_bottom_dist_to_5.asc --Grid of the public-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval public_open_dist_to_5.asc --Grid of the public-supply well open interval length data density, distance to reach 5 wells with

This data release includes grids representing the depth and thickness of drinking-water withdrawal zones, polygons of hydrogeologic settings, an inventory of sources of well construction data, and summaries of data comparisons used to assess the depth of groundwater used for drinking-water supplies in the United States. Well construction data sources are documented in Table1_DataSources.xlsx. Data comparisons using the Mann-Whitney test to assess similarity between hydrogeologic settings were used to justify combining data where they were sparse (compare_neighbors_all_domestic.txt and compare_neighbors_all_public.txt). Water-supply-well depth varies geographically by water use and the type of well, which illustrates the need to identify the depth of domestic drinking water withdrawal and depth of public supply drinking water withdrawal zones. Water-supply-well depth also varies by aquifer; therefore median values were calculated for each Principal Aquifer (PA), Secondary Hydrogeologic Region (SHR) between PAs and PA or SHR associated with overlying sediment polygons, where present, including glacial (G), coarse glacial (GC), and stream-valley alluvium (AV) polygons (all termed hydrogeologic settings here). A polygon shape file of hydrogeologic settings is included in this data release (HG_Settings.zip) and includes well counts and median thicknesses and depths for each area. This data release documents an inventory of well construction data sources and thickness and median top and bottom of drinking water depth zones by aquifer for domestic and public supplies. This data release includes equations used for estimating information for wells missing information on the depth to the top/length of the open interval. This data release contains: HG_Settings.zip --Shape file with well counts and median depth and thickness for hydrogeologic setting areas compare_neighbors_all_domestic.txt --results of Mann-Whitney tests to assess domestic-supply well construction data similarity between hydrogeologic settings compare_neighbors_all_public.txt --results of Mann-Whitney tests to assess public-supply well construction data similarity between hydrogeologic settings Depth_of_Drinking_Water_Supplies_Metadata03162021.xml --Metadata NonReferencedDomestic.txt --An inventory of domestic-supply well data that are not published elsewhere NonReferencedPublic.txt --An inventory of public-supply well data that are not published elsewhere Table1_DataSources.xlsx --An inventory of databases, references, state web sites, and individual state contacts for data sources. The logic behind data extraction algorithms is also defined for each data source. A tab delimited text version with the same name is also available. Lithology_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by lithology, overlying sediment, and well type HydrogeologicSetting_OpenIntervalLengthFit.txt --Parameters for equations used for estimating open intervals by hydrogeologic setting and well type domestic_grids.zip contains: domestic_bottom_dist_to_5.asc --Grid of domestic-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval domestic_open_dist_to_5.asc --Grid of domestic-supply well open interval length data density, distance to reach 5 wells with information on open interval length domestic_bottom_open.asc --Grid of domestic-supply well depth to the bottom of the open interval domestic_len_open.asc --Grid of domestic-supply well open-interval length domestic_top_open.asc --Grid of domestic-supply well depth to the top of the open interval public_grids.zip contains: public_bottom_dist_to_5.asc --Grid of the public-supply well open interval bottom depth data density, distance to reach 5 wells with information on the bottom of the open interval public_open_dist_to_5.asc --Grid of the public-supply well open interval length data density, distance to reach 5 wells with

Groundwater-quality data were collected from 648 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (514) were sampled from January through December 2016 and 60 of them were sampled in 2013 and 74 in 2014. The data were collected from seven types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality; major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply; enhanced trends networks, which are used to evaluate the time scales during which groundwater quality changes; vertical flow-path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths; flow path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths over a horizontal distance; and modeling support studies, which are used to provide data to support groundwater modeling. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium [VI] and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-1124 which is available at https://dx.doi.org/XXXXXX and in this data release. Some data from environmental samples collected in 2013-14 and quality-control samples collected in 2012-15 also are included in the associated data release. Data from samples collected in 2016 are associated with networks described in this report and have not been published previously; data from samples collected between 2012 and 2015 are associated with networks described in previous reports in this data series (Arnold and others, 2016a,b, 2017a,b, 2018a,b). There are 23 data tables included in this data release and they are referenced as tables 1-13 and appendix tables 4.10-4.19 in the larger work citation. There are 36 tables that are part of the larger work citation; the 13 tables not included in the data release are summary tables derived from some of the other tables (tables 1.1, 2.2-2.3, 3.1, 4.1-4.9). A version of table 1 is included in both the text and data release. This compressed file contains 23 files of groundwater-quality data in ASCII text tab-delimited format and one corresponding metadata in xml format that describes all the tables and attributes.

Groundwater-quality data were collected from 648 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program and are included in this report. Most of the wells (514) were sampled from January through December 2016 and 60 of them were sampled in 2013 and 74 in 2014. The data were collected from seven types of well networks: principal aquifer study networks, which are used to assess the quality of groundwater used for public water supply; land-use study networks, which are used to assess land-use effects on shallow groundwater quality; major aquifer study networks, which are used to assess the quality of groundwater used for domestic supply; enhanced trends networks, which are used to evaluate the time scales during which groundwater quality changes; vertical flow-path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths; flow path study networks, which are used to evaluate changes in groundwater quality from shallow to deeper depths over a horizontal distance; and modeling support studies, which are used to provide data to support groundwater modeling. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, radionuclides, and some special interest constituents (arsenic speciation, chromium [VI] and perchlorate). These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-1124 which is available at https://dx.doi.org/XXXXXX and in this data release. Some data from environmental samples collected in 2013-14 and quality-control samples collected in 2012-15 also are included in the associated data release. Data from samples collected in 2016 are associated with networks described in this report and have not been published previously; data from samples collected between 2012 and 2015 are associated with networks described in previous reports in this data series (Arnold and others, 2016a,b, 2017a,b, 2018a,b). There are 23 data tables included in this data release and they are referenced as tables 1-13 and appendix tables 4.10-4.19 in the larger work citation. There are 36 tables that are part of the larger work citation; the 13 tables not included in the data release are summary tables derived from some of the other tables (tables 1.1, 2.2-2.3, 3.1, 4.1-4.9). A version of table 1 is included in both the text and data release. This compressed file contains 23 files of groundwater-quality data in ASCII text tab-delimited format and one corresponding metadata in xml format that describes all the tables and attributes.

Groundwater-quality data were collected from 748 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from May 2012 through December 2013. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, and radionuclides. These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-997 which is available at http://dx.doi.org/10.3133/ds997 and in this data release. Quality-control samples also were collected; data from blank and replicate quality-control samples are included in the related report (DS-997) and this data release. This compressed file contains 28 files of groundwater-quality data in ASCII text tab-delimited format and 28 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project, May 2012 through December 2013.

Groundwater-quality data were collected from 748 wells as part of the National Water-Quality Assessment Project of the U.S. Geological Survey National Water-Quality Program from May 2012 through December 2013. The data were collected from four types of well networks: principal aquifer study networks, which assess the quality of groundwater used for public water supply; land-use study networks, which assess land-use effects on shallow groundwater quality; major aquifer study networks, which assess the quality of groundwater used for domestic supply; and enhanced trends networks, which evaluate the time scales during which groundwater quality changes. Groundwater samples were analyzed for a large number of water-quality indicators and constituents, including major ions, nutrients, trace elements, volatile organic compounds, pesticides, and radionuclides. These groundwater quality data are tabulated in a U.S. Geological Survey Data Series Report DS-997 which is available at http://dx.doi.org/10.3133/ds997 and in this data release. Quality-control samples also were collected; data from blank and replicate quality-control samples are included in the related report (DS-997) and this data release. This compressed file contains 28 files of groundwater-quality data in ASCII text tab-delimited format and 28 corresponding metadata in xml format for wells sampled for the U.S. Geological Survey National Water-Quality Assessment Project, May 2012 through December 2013.

This is a combined dataset from the USGS Orphaned Well Dataset (Grove and Merrill, 2022) and publicly available data from the USGS National Water Information System (NWIS) obtained via the Water Quality Portal using the USGS Python dataretrieval library. This dataset is composed of water quality measurements from groundwater sites located within 1 mile of the locations of unplugged orphaned wells listed in the United States Documented Unplugged Orphaned Oil and Gas Well Dataset. This dataset contains measurements of common water quality parameters (pH, temperature, specific conductance, TDS), dissolved light hydrocarbons and their isotopes (Methane, δ13C in methane, δ2H in methane, ethane, δ13C in ethane, propane, and butane), constituents that can indicate the presence of brines and geologic fluids and be used to assess corrosivity (calcium, chloride, bromide, alkalinity), measurements that can be used to assess the potential for biogenic methane production (sulfate, sulfur isotopes, oxidation/reduction potential), as well as isotopic tracers of hydrologic processes (δ2H and δ18O in water and tritium). The data include supporting information about the water quality measurement sites that can help provide context to the water quality measurements. The data is presented in several ways, including all individual measurements, the average water quality near each orphaned well in the dataset, water quality measurements averaged near orphaned well (less than 100 meters), and averaged for distances at further away (100 meters to 1.6 kilometers), as well as the combined subset of data where there are measurements for both the near (less than 100 meters) and far (between 100 meters an 1.6 kilometer) radius. This data release also includes the script and input file used to retrieve and format the data from NWIS to allow use in other projects.