This data release documents eight Microsoft Excel tables; four which contain data for understanding groundwater ages in the South East Coastal Plain (SECP), Coastal Lowlands (CLOW) and Mississippi Embayment and Texas Coastal Uplands (METX) aquifer systems and four that describe the data fields. Results described include dissolved gas modeling results, environmental tracer concentrations (tritium, tritiogenic helium-3, sulfur hexafluoride, and radiogenic helium-4), mean age and age distribution, and carbon-14 geochemical model input and results. Dissolved gas modeling results (DGmodel) 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 (TracerLPM) contain final models of groundwater age by calibration of lumped parameter models to tracer concentrations (Jurgens and others, 2012). 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. Additional results for select sites, identified with a “-1” or “-2” suffix to USGS Station ID, detail the estimated range corrected 14C activity and groundwater mean age as a result of uncertainty in 14C geochemical correction. Please see the processing steps below and the main manuscript for additional details on the results presented in this table. Carbon-14 geochemical model results (Carbon14) contain model inputs and final adjusted carbon-14 input to TracerLPM for determination of groundwater age.Carbon-14 adjustments were made using the revised Fontes and Garnier model (Han and Plummer, 2013).

This data release documents four tables that contain data for assessing the susceptibility of groundwater using environmental tracers collected from public-supply wells located in the Northern Atlantic Coastal Plain (NACP) Aquifer System and Piedmont and Blue Ridge Crystalline-Rock Aquifers of Eastern United States. Results for two modeling support studies located within the NACP are also included. Table 1 provides the primary results of this study and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations, as well as results of the tritium age classification, susceptibility index, the mean groundwater age, fraction of Modern water (water that was recharged after 1952), and detailed lumped parameter model calibration results of each sample in this study. Mean groundwater ages were determined by calibration of environmental tracers (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models for 231 public-supply 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 two, three, and four provide results in support of table 1. Table two 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 three reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results reported in table 2. The dry-air mixing ratio is the atmospheric concentration (assuming the water has a single age) at the time of gas-water equilibration and is calculated for transient atmospheric gas tracers such as sulfur hexafluoride and chlorofluorocarbons. Tritiogenic helium-3 is the concentration of helium-3 that resulted from the decay of tritium and radiogenic helium-4 is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. Table 4 reports results of calculated carbon-14 corrections caused by dissolution of carbonate minerals in the soil and saturated zone. Calculated carbon-14 corrections can be determined from analytical models of carbonate dissolution or from inverse geochemical modeling of the evolution of groundwater chemistry of a sample. The corrected carbon-14 concentration can be compared directly to carbon-14 atmospheric records, otherwise, dilution of the atmospheric record was inferred from Modern groundwater sample with 2 or more environmental tracers. 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 one through four. Please see processing steps in the general metadata file for more detailed information about the methods used to create the tables.

This data release documents four tables that contain data for assessing the susceptibility of groundwater using environmental tracers collected from public-supply wells located in the Northern Atlantic Coastal Plain (NACP) Aquifer System and Piedmont and Blue Ridge Crystalline-Rock Aquifers of Eastern United States. Results for two modeling support studies located within the NACP are also included. Table 1 provides the primary results of this study and it contains condensed results from dissolved gas modeling and calculated environmental tracer concentrations, as well as results of the tritium age classification, susceptibility index, the mean groundwater age, fraction of Modern water (water that was recharged after 1952), and detailed lumped parameter model calibration results of each sample in this study. Mean groundwater ages were determined by calibration of environmental tracers (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models for 231 public-supply 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 two, three, and four provide results in support of table 1. Table two 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 three reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results reported in table 2. The dry-air mixing ratio is the atmospheric concentration (assuming the water has a single age) at the time of gas-water equilibration and is calculated for transient atmospheric gas tracers such as sulfur hexafluoride and chlorofluorocarbons. Tritiogenic helium-3 is the concentration of helium-3 that resulted from the decay of tritium and radiogenic helium-4 is the amount of helium generated from the decay of uranium and thorium in aquifer sediments. Table 4 reports results of calculated carbon-14 corrections caused by dissolution of carbonate minerals in the soil and saturated zone. Calculated carbon-14 corrections can be determined from analytical models of carbonate dissolution or from inverse geochemical modeling of the evolution of groundwater chemistry of a sample. The corrected carbon-14 concentration can be compared directly to carbon-14 atmospheric records, otherwise, dilution of the atmospheric record was inferred from Modern groundwater sample with 2 or more environmental tracers. 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 one through four. Please see processing steps in the general metadata file for more detailed information about the methods used to create the tables.

The U.S. Geological Survey (USGS) undertook a 5-year study beginning in 2016 to assess groundwater availability for the aquifers proximal to the Gulf of Mexico from the Texas-Mexico border to the western part of the panhandle of Florida; these aquifers are collectively referred to as the coastal lowlands aquifer system. This study is one of several regional groundwater availability studies being done as part of the USGS Water Availability and Use Science Program. Groundwater from the coastal lowlands aquifer system is used mainly for public, irrigation, and industrial supply. During the first two years of the study, the team developed an updated conceptual model of the hydrogeologic framework of the coastal lowlands aquifer system, and in support, a defining compilation of hydrogeologic data. By referencing the data in this compilation, extents of the coastal lowland aquifers were able to be updated and digitized. This data release contains the shapefiles representing the surficial extents of the respective aquifers within the coastal lowlands: the Chicot aquifer, Evangeline aquifer, Burkeville Confining Unit, Jasper aquifer, and Catahoula to the top of the Vicksburg-Jackson confining unit.

The U.S. Geological Survey (USGS) undertook a 5-year study beginning in 2016 to assess groundwater availability for the aquifers proximal to the Gulf of Mexico from the Texas-Mexico border to the western part of the panhandle of Florida; these aquifers are collectively referred to as the coastal lowlands aquifer system. This study is one of several regional groundwater availability studies being done as part of the USGS Water Availability and Use Science Program. Groundwater from the coastal lowlands aquifer system is used mainly for public, irrigation, and industrial supply. During the first two years of the study, the team developed an updated conceptual model of the hydrogeologic framework of the coastal lowlands aquifer system, and in support, a defining compilation of hydrogeologic data. By referencing the data in this compilation, extents of the coastal lowland aquifers were able to be updated and digitized. This data release contains the shapefiles representing the surficial extents of the respective aquifers within the coastal lowlands: the Chicot aquifer, Evangeline aquifer, Burkeville Confining Unit, Jasper aquifer, and Catahoula to the top of the Vicksburg-Jackson confining unit.

The U.S. Geological Survey (USGS) undertook a 5-year study beginning in 2016 to assess groundwater availability for the aquifers proximal to the Gulf of Mexico from the Texas-Mexico border to the western part of the panhandle of Florida; these aquifers are collectively referred to as the coastal lowlands aquifer system. This study is one of several regional groundwater availability studies being done as part of the USGS Water Availability and Use Science Program. Groundwater from the coastal lowlands aquifer system is used mainly for public, irrigation, and industrial supply. Land-surface subsidence related to groundwater pumping is an issue of ongoing concern within this study area. During the first two years of the study, the team developed an updated conceptual model of the hydrogeologic framework of the aquifer system, which lead to initial estimates of major water budget components such as recharge, surface-water/groundwater exchange, and coastal discharge. This data release documents the hydrogeologic data that were compiled and used to define the hydrogeologic framework.