This data release contains groundwater-quality data and well information for the glacial aquifer system in the northern USA. Water-quality data and well information were derived from a dataset compiled from three sources: The U.S. Geological Survey (USGS) National Water Information System (NWIS; USGS, 1998, 2002), the U.S. Environmental Protection Agency (USEPA) Safe Drinking Water Information System (SDWIS; USEPA, 2013), and numerous agencies and organizations at the state, regional, and local level. The data compilation of the National Water Quality Program’s groundwater assessment team is an internal dataset informally referred to as the National Groundwater Aggregation (NGA). The current study of groundwater quality in the glaciated U.S. (Erickson and others, 2019) considers only parameters with benchmarks from wells in the national groundwater aggregation—data from springs were not used. Data were screened for sample dates of 2005 or later, and the most recent sample at each site was used. This data release includes a table of benchmarks and thresholds. “Benchmark” is a generic term for any standard, regulation, guideline, or criteria against which constituent concentrations are compared. The threshold is the value against which measured concentrations of constituents in water samples can be compared to help assess the potential effects of contaminants on water quality. The table of water-quality results includes the concentration of constituents relative to their health-based or non-health benchmark, and a flag to indicate if the concentration is low, medium, or high relative to the benchmark. A table of site information includes attributes for each well such as the source of the water-quality data and well information, the state, water use code, depth (if available), and the 17 hydrogeologic terrane from Yager and others (2018). Each hydrogeologic terrane contains Quaternary sediment that is derived from a common depositional history and can be characterized by similar texture and thickness. Each of the 17 hydrogeologic terranes was divided into 30 equal-areas (cells) based on the method of Scott (1990). This cell number for each well is included in the table of site information. An equal-area assessment was used to show the proportion of the aquifer affected by high, medium, and low concentrations of selected constituents at the aquifer scale and terrane scale (Belitz and others, 2010). The equal-area cells were also used with population data (Erickson and others, 2019, supplemental information) to determine aquifer- and terrane-scale proportions of the population affected by high, medium, and low concentrations of selected constituents. A shape file of the hydrogeologic terranes and equal-area cells is included in this data release. A table of well construction information includes attributes for each well such as the source of the well information, the state, well depth, screen length (if available), and the hydrogeologic terrane from Yager and others (2018). Information in this table is from a well construction database compiled from several sources to obtain information on well depths and screened intervals of domestic and public supply wells producing groundwater from Quaternary sediments in the U.S. within the glacial extent. Domestic-supply well data were compiled from a lithologic database (Bayless and others, 2017) as modified by Yager and others (2018), the USGS NWIS (USGS, 2016), and several state well log databases (Erickson and others, 2019, supplemental information). The state databases were accessed to add well records in areas where information from the lithologic and NWIS databases was sparse. Public-supply well data were compiled from the list of public water-supply wells in the water-use database of Yager and others (2018). This data release contains four tables and one shape file: Drinking_Water_QW_Glacial_Aquifer_System_Results.txt Drinking_Water_QW_Glacial_Aquifer_System_Sites.txt

This data release contains input data used in model development and TIF raster files used to predict the probability of low dissolved oxygen (DO) and high dissolved iron (Fe) in groundwater within the glacial aquifer system in the northern continental United States. Input data include measured DO and Fe concentrations at groundwater wells, and associated predictor variable data. The probability of low DO and high Fe was predicted using boosted regression tree methods using the gbm package in R (v. 4.0.0) in RStudio (v. 1.2.5042). The response variables for individual models were the occurrence of: (1) DO ≤0.5 mg/L, (2) DO ≤2 mg/L, and (3) Fe >100 µg/L. Water-quality data were compiled from three sources, as described in Wilson and others (2019): a compilation of data from numerous agencies and organizations at the state, regional, and local level; the U.S. Geological Survey National Water Information System; and the U.S. Environmental Protection Agency Safe Drinking Water Information System. The resultant datasets consisted of 9,398 DO and 17,422 Fe measurements across the study area. A total of 108 predictor variables were originally considered for model development which included well characteristics, soil properties, aquifer properties, predicted nitrate, hydrologic position on the landscape, and groundwater age. After model refinement, a total of 86, 94, and 40 predictor variables were used for predicting the probability of low DO (0.5 and 2 mg/L) and high Fe, respectively.

This data release contains input data used in model development and TIF raster files used to predict the probability of low dissolved oxygen (DO) and high dissolved iron (Fe) in groundwater within the glacial aquifer system in the northern continental United States. Input data include measured DO and Fe concentrations at groundwater wells, and associated predictor variable data. The probability of low DO and high Fe was predicted using boosted regression tree methods using the gbm package in R (v. 4.0.0) in RStudio (v. 1.2.5042). The response variables for individual models were the occurrence of: (1) DO ≤0.5 mg/L, (2) DO ≤2 mg/L, and (3) Fe >100 µg/L. Water-quality data were compiled from three sources, as described in Wilson and others (2019): a compilation of data from numerous agencies and organizations at the state, regional, and local level; the U.S. Geological Survey National Water Information System; and the U.S. Environmental Protection Agency Safe Drinking Water Information System. The resultant datasets consisted of 9,398 DO and 17,422 Fe measurements across the study area. A total of 108 predictor variables were originally considered for model development which included well characteristics, soil properties, aquifer properties, predicted nitrate, hydrologic position on the landscape, and groundwater age. After model refinement, a total of 86, 94, and 40 predictor variables were used for predicting the probability of low DO (0.5 and 2 mg/L) and high Fe, respectively.

Water level altitudes were measured at 275 observation wells and 1 supply well screened in the upper glacial and Magothy aquifers during April and May of 2016. This shapefile consists of the locations of those sites and includes water level altitude data stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and altitude values in this point shapefile are also presented in Sheet 1 of Scientific Investigations Map 3398.

Water level altitudes were measured at 334 observation wells and 1 supply well screened in the upper glacial and Magothy aquifers during April and May of 2013. This shapefile consists of the locations of those sites and includes water level altitude data stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and altitude values in this point shapefile are also presented in Sheet 1 of Scientific Investigations Map 3326.

Water level altitudes were measured at 334 observation wells and 1 supply well screened in the upper glacial and Magothy aquifers during April and May of 2013. This shapefile consists of the locations of those sites and includes water level altitude data stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and altitude values in this point shapefile are also presented in Sheet 1 of Scientific Investigations Map 3326.

A comprehensive study to evaluate water-quality trends in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States was completed by the U.S. Geological Survey (USGS) in cooperation with the International Joint Commission and International Souris River Board. This page contains water-quality data for stream and reservoir sites in the Souris River Basin in North Dakota, Saskatchewan, and Manitoba. Each file contains information on major ions (MI), nutrients (NUT), trace metals (TM), sediment (SED), and dissolved oxygen (PHY). These data contain numerous columns that are described in the entity and attributes of these files. These files contain the water-quality observations for the statistical summary tables in the report cited in this data release (Nustad and Tatge, 2023).The siteinfo.table.csv file can be used to cross reference the sites with the main report (Nustad and Tatge, 2023).

A comprehensive study to evaluate water-quality trends in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States was completed by the U.S. Geological Survey (USGS) in cooperation with the International Joint Commission and International Souris River Board. This page contains water-quality data for stream and reservoir sites in the Souris River Basin in North Dakota, Saskatchewan, and Manitoba. Each file contains information on major ions (MI), nutrients (NUT), trace metals (TM), sediment (SED), and dissolved oxygen (PHY). These data contain numerous columns that are described in the entity and attributes of these files. These files contain the water-quality observations for the statistical summary tables in the report cited in this data release (Nustad and Tatge, 2023).The siteinfo.table.csv file can be used to cross reference the sites with the main report (Nustad and Tatge, 2023).

A comprehensive study to evaluate water-quality trends in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States was completed by the U.S. Geological Survey (USGS) in cooperation with the International Joint Commission and International Souris River Board. This page contains water-quality data for stream and reservoir sites in the Souris River Basin in North Dakota, Saskatchewan, and Manitoba. Each file contains information on major ions (MI), nutrients (NUT), trace metals (TM), sediment (SED), and dissolved oxygen (PHY). These data contain numerous columns that are described in the entity and attributes of these files. These files contain the water-quality observations for the statistical summary tables in the report cited in this data release (Nustad and Tatge, 2023).The siteinfo.table.csv file can be used to cross reference the sites with the main report (Nustad and Tatge, 2023).

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.