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.

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.

This data set represents the extent of the Texas coastal uplands aquifer system in Texas.

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 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).

The High Plains aquifer extends from about 32 degrees to almost 44 degrees north latitude and from about 96 degrees 30 minutes to 106 degrees west longitude. The aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital dataset consists of three sets of water-level measurements. The first set are the supplemental water-level measurements for 547 wells screened in the High Plains aquifer, not located in New Mexico, measured in predevelopment and at least once for 2015 through 2018, but not for 2019. These supplemental measurements were used to calculate historical water-level change values for predevelopment to 2015 to 2018 and approximate water-level change values from predevelopment to 2019 to substantiate the map of water-level changes, predevelopment (about 1950) to 2019 (figure 1 in https://doi.org/10.3133/sir20235143). The water-level measurements used to calculate historical water-level changes from predevelopment are (1) 218 wells measured in predevelopment and in 2018, but not measured in 2019, which are used to calculate water-level change, predevelopment to 2018, (2) 152 wells measured in predevelopment and in 2017, but not measured in 2018 or 2019, which are used to calculate water-level change, predevelopment to 2017, (3) 117 wells measured in predevelopment and in 2016, but not measured in 2017, 2018, or 2019, which are used to calculate water-level change, predevelopment to 2016, and (4) 60 wells measured in predevelopment and in 2015, but not measured in 2016, 2017, 2018, or 2019, which are used to calculate water-level change, predevelopment to 2015. The second and third sets of water-level measurements were used to approximate water-level change, predevelopment to 2019, but did not have predevelopment water-level measurements. The second set included 292 wells, which were located in areas where water level declines from predevelopment to 1980 were 50 feet or more (Luckey and others, 1981; Cederstrand and Becker, 1999) and were measured in 1980 and in 2019, but not measured in the predevelopment period. For these wells, approximate water-level changes, predevelopment to 2019, were calculated as the starting value of the polygon range (for example 50 ft for the polygon of declines from 50 to 75 ft) from the map of water-level change, predevelopment to 1980, plus measured water-level change from 1980 to 2019. The third set of water-level measurements used to calculate approximate water-level changes were from 1,213 wells that were measured on or before 6/15/1978 (termed post-development) and in 2019, but not in the predevelopment period. For these wells, approximate water-level changes, predevelopment to 2019, were calculated as the water level, 2019, minus water level, post-development.

The High Plains aquifer extends from about 32 degrees to almost 44 degrees north latitude and from about 96 degrees 30 minutes to 106 degrees west longitude. The aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. This digital dataset consists of three sets of water-level measurements. The first set are the supplemental water-level measurements for 547 wells screened in the High Plains aquifer, not located in New Mexico, measured in predevelopment and at least once for 2015 through 2018, but not for 2019. These supplemental measurements were used to calculate historical water-level change values for predevelopment to 2015 to 2018 and approximate water-level change values from predevelopment to 2019 to substantiate the map of water-level changes, predevelopment (about 1950) to 2019 (figure 1 in https://doi.org/10.3133/sir20235143). The water-level measurements used to calculate historical water-level changes from predevelopment are (1) 218 wells measured in predevelopment and in 2018, but not measured in 2019, which are used to calculate water-level change, predevelopment to 2018, (2) 152 wells measured in predevelopment and in 2017, but not measured in 2018 or 2019, which are used to calculate water-level change, predevelopment to 2017, (3) 117 wells measured in predevelopment and in 2016, but not measured in 2017, 2018, or 2019, which are used to calculate water-level change, predevelopment to 2016, and (4) 60 wells measured in predevelopment and in 2015, but not measured in 2016, 2017, 2018, or 2019, which are used to calculate water-level change, predevelopment to 2015. The second and third sets of water-level measurements were used to approximate water-level change, predevelopment to 2019, but did not have predevelopment water-level measurements. The second set included 292 wells, which were located in areas where water level declines from predevelopment to 1980 were 50 feet or more (Luckey and others, 1981; Cederstrand and Becker, 1999) and were measured in 1980 and in 2019, but not measured in the predevelopment period. For these wells, approximate water-level changes, predevelopment to 2019, were calculated as the starting value of the polygon range (for example 50 ft for the polygon of declines from 50 to 75 ft) from the map of water-level change, predevelopment to 1980, plus measured water-level change from 1980 to 2019. The third set of water-level measurements used to calculate approximate water-level changes were from 1,213 wells that were measured on or before 6/15/1978 (termed post-development) and in 2019, but not in the predevelopment period. For these wells, approximate water-level changes, predevelopment to 2019, were calculated as the water level, 2019, minus water level, post-development.