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 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 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 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.

Data used to model and map pH and redox conditions in groundwater in the Northern Atlantic Coastal Plain aquifer system, eastern USA, are documented in this data release. The models use as input data measurements of pH and dissolved oxygen concentrations at about 3000 to 5000 wells, which were compiled primarily from U.S. Geological Survey and U.S. Environmental Protection Agency databases. The boosted regression trees machine learning method was used to build the models. Explanatory variables (predictors) describe geology, hydrology, chemistry, physical characteristics, anthropogenic influence, metrics from a groundwater flow model, and groundwater residence times in the aquifer system. Data for four models are documented--one model for pH and one model each for the probability of dissolved oxygen less than three threshold values (0.5, 1, and 2 milligrams per liter). The data are provided in data tables and raster files, organized as follows. There is one data table for the well data used to develop all four models (well data). There is one zipped group of 10 files (one for each aquifer) for explanatory input data used to make predictions at grid points (prediction input). There are 9 zipped groups of files for model output; these include 1 zip file of predictions at grid points for each of the 4 models (prediction output), 1 zip file for combined pH and dissolved oxygen predictions (combined prediction output); and 4 zip files of uncertainty intervals for predictions for each of the 4 models (uncertainty output). Filenames for prediction input and for model output are distinguished by codes abbreviating the aquifer name and position in the vertical stack of 19 regional aquifers and confining units, as follows: Surficial aquifer, 1surf; Upper Chesapeake aquifer, 3upch; Lower Chesapeake aquifer, 5loch; Piney Point aquifer, 7pipt; Aquia aquifer, 9aqia; Monmouth - Mt. Laurel Aquifer, 11moml; Matawan aquifer, 13mtwn; Magothy Aquifer, 15mgty; Potomac-Patapsco aquifer, 17popt; Potomac-Patuxent aquifer, 19popx. The data release also contains a tif-format raster file of the prediction grid and two data tables that separately describe the explanatory variables (predictors) and their sources.

The depth to water table was measured at 276 groundwater monitoring wells (observation and supply) screened in the upper glacial and Magothy aquifers during April and May of 2016. This shapefile consists of the locations of those sites where water levels were measured and includes depth-to-water values which are stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and depth-to-water values in this digital data set are also presented in Sheet 4 of Scientific Investigations Map 3398.

The depth to water table was measured at 276 groundwater monitoring wells (observation and supply) screened in the upper glacial and Magothy aquifers during April and May of 2016. This shapefile consists of the locations of those sites where water levels were measured and includes depth-to-water values which are stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and depth-to-water values in this digital data set are also presented in Sheet 4 of Scientific Investigations Map 3398.

Groundwater is a vital resource in the Mississippi embayment physiographic region (Mississippi embayment) of the central United States and can be limited in some areas by high concentrations of trace elements. The concentration of trace elements in groundwater is largely driven by oxidation-reduction (redox) processes. Redox processes are a group of biotically driven reactions in which energy is derived from the exchange of electrons. In groundwater, this commonly occurs through decomposition of organic matter (carbon) by microbes, which consumes dissolved oxygen (DO). Under low DO conditions, iron (Fe), manganese, and arsenic can dissolve from coatings on aquifer sediments and be released into groundwater. Therefore, predictions of redox conditions (using DO and Fe) are important in the Mississippi embayment for a better understanding of the potential zones of high trace elements in drinking-water aquifers. The Mississippi embayment includes two principal regional aquifer systems: the Quaternary Mississippi River Valley alluvial aquifer (MRVA) and the Mississippi embayment aquifer system, which includes deeper Tertiary aquifers and confining units. Based on the distribution of groundwater use for drinking water, the modeling focused on the MRVA, the middle Claiborne aquifer (MCAQ), and the lower Claiborne aquifer (LCAQ). Machine learning was used to predict redox conditions—including the probability of exceeding a DO concentration of 1 milligram per liter (mg/L) and Fe concentrations—across the MRVA, MCAQ, and LCAQ. Boosted regression tree (BRT) models (Elith and others, 2008; Kuhn and Johnson, 2013) were developed to predict DO probability and Fe concentration to 1-kilometer (km) raster grid cells of the National Hydrologic Grid (Clark and others, 2018) for 7 aquifer layers (1 MRVA, 4 MCAQ, 2 LCAQ) following the hydrogeologic framework of Hart and others (2008). Explanatory variables for the BRT models included attributes associated with well location and construction, surficial variables (such as soils and land use), and variables extracted from a MODFLOW groundwater flow model for the Mississippi embayment (Haugh and others, 2020a; Haugh and others, 2020b). Output from DO and Fe models were used to classify redox zones, including anoxic, mixed anoxic, mixed oxic, and oxic conditions. Oxic conditions included areas where the probability of exceeding a DO concentration of 1 mg/L was greater than 80 percent and iron was less than 1,000 µg/L. Anoxic conditions included areas where the probability of exceeding a DO concentration of 1 mg/L was less than 10 percent. Mixed conditions include anywhere that the predicted DO probability was greater than or equal to 10 percent and less than or equal to 80 percent, and either less than 500 µg/L iron (mixed oxic) or greater than or equal to 500 µg/L iron (mixed anoxic). Prediction intervals were calculated for DO and Fe by bootstrapping raster-cell predictions following methods from Ransom and others (2017). For a full description of modeling workflow and final model selection see Knierim and others (2020).

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.

The depth to water table was measured at 335 groundwater monitoring wells (observation and supply) screened in the upper glacial and Magothy aquifers during April and May of 2013. This shapefile consists of the locations of those sites where water levels were measured and includes depth-to-water values which are stored in the attribute table. The shapefile was created and intended for use with geographic information system (GIS) software. The measurement locations and depth-to-water values in this digital data set are also presented in Sheet 4 of Scientific Investigations Map 3326.