Groundwater residence times were simulated for the major regional aquifers of the Northern Atlantic Coastal Plain aquifer system from New York to North Carolina using particle tracking in a regional groundwater flow model. Millions of particles were distributed throughout the aquifers of the North Atlantic Coastal Plain in a MODFLOW model with a volume-weighted algorithm, then tracked backwards using MODPATH6 (Pollock, 2012) until termination of their paths at their sources of origin, usually the simulated water table. Particles were tracked under simulated transient hydrologic conditions from the reference time of January 1, 2018 backwards to 1900, then under simulated steady-state conditions prior to 1900 until eventual termination of their paths. The simulated residence time, or simulated age, of each particle is the time each particle took to travel backwards from its initial (year 2018) location in the aquifer to its source of origin. Simulated residence times of many individual particles were statistically aggregated for every model grid cell within each of 10 North Atlantic Coastal Plain regional aquifer units. From top to bottom, these include the surficial aquifer, the Upper Chesapeake aquifer, the Lower Chesapeake aquifer, the Piney Point aquifer, the Aquia aquifer, the Monmouth-Mount Laurel aquifer, the Matawan aquifer, the Magothy aquifer, the Potomac-Patapsco aquifer, and the Potomac-Patuxent aquifer. All model cells are one square mile in area but vary in thickness depending on the aquifer and the location. For all statistical computations, individual particle residence times were first modified to limit the statistical influence of unreasonably high and low values resulting from limitations in the simulation approach. Simulated particle residence time values less than or equal to 0.001 years were assigned this value as a minimum, which is less than one day. Particle residence times greater than 10,000,000 years were censored at this value, which is the approximate maximum reasonable residence time for the aquifer system. Statistics computed from the modified simulated residence-time values for each model cell for each aquifer unit include the number of particles originating in the cell, mean residence time, median residence time, minimum residence time, maximum residence time, 10th percentile of residence times, 25th percentile of residence times, 75th percentile of residence times, and 90th percentile of residence times. A table of these computed statistics is provided for each of the ten aquifer units, with entries organized by model cell identification number, which may be used to spatially orient the residence time statistics. A polygon shapefile of the groundwater model grid is also provided, with model-cell statistics joined for all aquifers.

Groundwater residence times and flow path lengths were simulated for two major aquifers of the Mississippi embayment region using particle tracking (Pollock, 2012; Starn and Belitz, 2018) in a regional groundwater-flow model (Haugh and others, 2020). The Mississippi embayment physiographic region includes two principal aquifer systems: the surficial aquifer system, which is dominated by the Quaternary Mississippi River Valley alluvial aquifer (MRVA), and the Mississippi embayment aquifer system, which includes deeper Tertiary aquifers and confining units. The groundwater residence time simulation focused on the MRVA and two hydrogeologic units of the Claiborne Group (CLBG) from the deeper system, including the middle Claiborne aquifer (MCAQ) and lower Claiborne aquifer (LCAQ). A previously published groundwater flow model of the Mississippi embayment regional aquifer system provided the flow field for this analysis (Clark and Hart, 2009; Clark and others, 2011; and Haugh and others, 2020). Raster files were produced for seven model layers following the hydrogeologic framework for the MODFLOW groundwater-flow model of the Mississippi embayment from Clark and Hart (2009): one for the MRVA and six for the middle and lower Claiborne aquifers including four representing the MCAQ (layers 5 – 8) and two representing the LCAQ (layers 9 and 10). To determine the groundwater residence time, particles were distributed in model layers representing these aquifers using a volume-weighted algorithm then back-tracked until the particles exited the aquifer system, usually at the water-table surface. Particles were tracked under transient hydrologic conditions from March 31, 2014 backwards to January 1, 1870, then under steady-state conditions until they exited the aquifer system. The simulated residence time of each particle is the time the particle took to travel backwards from its initial location in the aquifer to its source of origin. Groundwater-residence time metrics were generated by statistically summarizing individual particles that started within each model cell. The flow-model grid resolution of one square mile was used to simulate groundwater residence times. The data were then resampled to a 1-square kilometer resolution of the National Hydrologic Grid (Clark and others, 2018). Computed metrics included the minimum, mean, maximum, standard deviation, as well as the 10th-, 20th-, 30th-, 40th-, 50th-, 60th-,70th-, 80th-, and 90th-percentiles along with the minimum, median, and maximum flow path length. Additionally, the portion of young groundwater (< 65 years old) and the mean residence time of the young portion were computed.

Groundwater residence times and flow path lengths were simulated for two major aquifers of the Mississippi embayment region using particle tracking (Pollock, 2012; Starn and Belitz, 2018) in a regional groundwater-flow model (Haugh and others, 2020). The Mississippi embayment physiographic region includes two principal aquifer systems: the surficial aquifer system, which is dominated by the Quaternary Mississippi River Valley alluvial aquifer (MRVA), and the Mississippi embayment aquifer system, which includes deeper Tertiary aquifers and confining units. The groundwater residence time simulation focused on the MRVA and two hydrogeologic units of the Claiborne Group (CLBG) from the deeper system, including the middle Claiborne aquifer (MCAQ) and lower Claiborne aquifer (LCAQ). A previously published groundwater flow model of the Mississippi embayment regional aquifer system provided the flow field for this analysis (Clark and Hart, 2009; Clark and others, 2011; and Haugh and others, 2020). Raster files were produced for seven model layers following the hydrogeologic framework for the MODFLOW groundwater-flow model of the Mississippi embayment from Clark and Hart (2009): one for the MRVA and six for the middle and lower Claiborne aquifers including four representing the MCAQ (layers 5 – 8) and two representing the LCAQ (layers 9 and 10). To determine the groundwater residence time, particles were distributed in model layers representing these aquifers using a volume-weighted algorithm then back-tracked until the particles exited the aquifer system, usually at the water-table surface. Particles were tracked under transient hydrologic conditions from March 31, 2014 backwards to January 1, 1870, then under steady-state conditions until they exited the aquifer system. The simulated residence time of each particle is the time the particle took to travel backwards from its initial location in the aquifer to its source of origin. Groundwater-residence time metrics were generated by statistically summarizing individual particles that started within each model cell. The flow-model grid resolution of one square mile was used to simulate groundwater residence times. The data were then resampled to a 1-square kilometer resolution of the National Hydrologic Grid (Clark and others, 2018). Computed metrics included the minimum, mean, maximum, standard deviation, as well as the 10th-, 20th-, 30th-, 40th-, 50th-, 60th-,70th-, 80th-, and 90th-percentiles along with the minimum, median, and maximum flow path length. Additionally, the portion of young groundwater (< 65 years old) and the mean residence time of the young portion were computed.

This data release contains simulation results from fifteen transient, regional-scale numerical models of the Long Island aquifer system that predict aquifer conditions resulting from possible future changes in pumping and recharge stresses and sea level altitude. These models are based on the MODFLOW 6 numerical model that is documented in Walter and others (2024), which simulates historical water levels, streamflows, and the position of the saltwater interface in response to time-varying changes in pumping and recharge stresses for the period 1900-2019. The archive for that model is available online (Jahn and others, 2024). Fifteen model-input data sets of possible future scenarios are used to simulate aquifer conditions at annual and seasonal time scales under a variety of recharge, pumping, and sea level rise (3, 6, and 9 feet) stresses. This data release contains descriptions of the fifteen model scenarios, the model input files, and software to allow the user to run the models for each of the fifteen scenarios. Detailed instructions on how to run the models are documented in ReadMe_Main.txt. First posted August 16, 2024, ver 1.0 Revised June 2025, ver 1.1 Version 1.1: This version of the dataset now includes the model files for scenario 7 (sc_7) extended out to 30 simulated years, and the 1000 mg/L shapefiles for scenario 7 (sc_7) have also been updated accordingly. The superfluous copies of the isochlor shapefiles were removed for all scenarios. Version 1.0: In this version of the dataset, scenario 7 (sc_7) was simulated for 25 years, rather than the 30 years the other scenarios were simulated. Thus, the scenario 7 (sc_7) shapefiles for the 1000 mg/L isochlors were showing results that were short 5 years of simulation. All of the scenarios each included a superfluous copy of the isochlor shapefiles (following naming convention: "sc_##_1000mgL_isochlor") that did not need to be included in the release. These superfluous copies were not described in the readme and were simply duplicates of data already in the release.

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 data set pp1773_extents contains polygon datasets that represent the areal extents of each of the 16 hydrogeologic units of the of the Atlantic Coastal Plain of North and South Carolina. [The total areal extent includes a small area in southeastern Virginia, the Atlantic Coastal Plain within North Carolina and South Carolina, and a region in southeast Georgia within the Atlantic Coastal Plain.] Each hydrogeological unit is referred to as its model layer number as represented in the report PP1773. For clarity, they are listed below along with the aquifer unit or confining unit name in North Carolina and its correlated unit name in South Carolina. L1 Surficial aquifer L2 Yorktown confining unit / Upper Floridan confining unit L3 Yorktown aquifer / Upper Floridan aquifer L4 Castle Hayne - Pungo River confining unit / Middle Floridan confining unit (To be referred to as "Castle Hayne / Middle Floridan confining unit" in this document) L5 Castle Hayne - Pungo River aquifer / Middle Floridan aquifer (To be referred to as "Castle Hayne - Middle Floridan aquifer" in this document) L6 Beaufort confing unit / Gordon confining unit L7 Beaufort aquifer / Gordon aquifer L8 Peedee confining unit / Crouch Branch confining unit L9 Peedee aquifer / Crouch Branch aquifer L10 Black Creek confining unit / McQueen Branch confining unit L11 Black Creek aquifer / McQueen Branch aquifer L12 Upper Cape Fear confining unit / Charleston confining unit L13 Upper Cape Fear aquifer / Charleston aquifer L14 Lower Cape Fear confining unit / Gramling confining unit L15 Lower Cape Fear aquifer / Gramling aquifer L16 Lower Cretaceous confining unit and aquifer Spatial data set pp1773_layer1_extent represents the extent of the top of the surficial aquifer, which is Layer 1 in the groundwater model used to simulate the aquifer system described in PP 1773. The surficial aquifer is the uppermost aquifer. It is an unconfined aquifer that is uniformly present except where it is incised by streams. The top of the surficial aquifer is equivalent to the land surface. The extent was derived primarily by geologic and hydraulic properties, as the surficial aquifer is an unconfined layer primarily composed of sediments of Quaternary age, plus some older sediments in areas due to a different stratigraphic position of the first underlying confining layer. Spatial data set pp_1773_layer_2 is the Yorktown/Upper Floridan confining unit. It is not composed of a single unit because the unit's series of clay and silt beds vary greatly in stratigraphic position. Spatial dataset pp1773_layer3_extent represents the extent of the Yorktown/Upper Floridan aquifer. The Yorktown aquifer is present only in the northern half of the North Carolina Coastal Plain. Outliers exist in Robeson, Bladen and Dublin counties, but are not separated from the surficial aquifer by a confining unit, and not considered a distinct aquifer in these areas. The Upper Floridan aquifer extent covers a southern portion of South Carolina and southern portion of Georgia. Spatial dataset pp1773_layer4_extent represents the extent of the Castle Hayne/Middle Floridan confining unit. The Castle Hayne confining unit consists of beds of clay and silt that vary in stratigraphic position and are absent in a number of areas in the central and southern North Carolina Coastal Plain. The Middle Floridan confining unit extends from South Carolina to southern Georgia. It is not continuous with the Castle Hayne confining unit. Spatial dataset pp1773_layer5_extent represents the extent of the Castle Hayne/Middle Floridan aquifer. The Castle Hayne aquifer is located in the central and southern North Carolina Coastal Plain; the Middle Floridan aquifer is more south, in southern South Carolina and southern Georgia. Spatial dataset pp1773_layer6_extent represents the extent of the Beaufort/Gordon confining unit. The Beaufort confining unit is located in northeastern North Carolina and southeastern Virginia. It is best developed in

The data set pp1773_extents contains polygon datasets that represent the areal extents of each of the 16 hydrogeologic units of the of the Atlantic Coastal Plain of North and South Carolina. [The total areal extent includes a small area in southeastern Virginia, the Atlantic Coastal Plain within North Carolina and South Carolina, and a region in southeast Georgia within the Atlantic Coastal Plain.] Each hydrogeological unit is referred to as its model layer number as represented in the report PP1773. For clarity, they are listed below along with the aquifer unit or confining unit name in North Carolina and its correlated unit name in South Carolina. L1 Surficial aquifer L2 Yorktown confining unit / Upper Floridan confining unit L3 Yorktown aquifer / Upper Floridan aquifer L4 Castle Hayne - Pungo River confining unit / Middle Floridan confining unit (To be referred to as "Castle Hayne / Middle Floridan confining unit" in this document) L5 Castle Hayne - Pungo River aquifer / Middle Floridan aquifer (To be referred to as "Castle Hayne - Middle Floridan aquifer" in this document) L6 Beaufort confing unit / Gordon confining unit L7 Beaufort aquifer / Gordon aquifer L8 Peedee confining unit / Crouch Branch confining unit L9 Peedee aquifer / Crouch Branch aquifer L10 Black Creek confining unit / McQueen Branch confining unit L11 Black Creek aquifer / McQueen Branch aquifer L12 Upper Cape Fear confining unit / Charleston confining unit L13 Upper Cape Fear aquifer / Charleston aquifer L14 Lower Cape Fear confining unit / Gramling confining unit L15 Lower Cape Fear aquifer / Gramling aquifer L16 Lower Cretaceous confining unit and aquifer Spatial data set pp1773_layer1_extent represents the extent of the top of the surficial aquifer, which is Layer 1 in the groundwater model used to simulate the aquifer system described in PP 1773. The surficial aquifer is the uppermost aquifer. It is an unconfined aquifer that is uniformly present except where it is incised by streams. The top of the surficial aquifer is equivalent to the land surface. The extent was derived primarily by geologic and hydraulic properties, as the surficial aquifer is an unconfined layer primarily composed of sediments of Quaternary age, plus some older sediments in areas due to a different stratigraphic position of the first underlying confining layer. Spatial data set pp_1773_layer_2 is the Yorktown/Upper Floridan confining unit. It is not composed of a single unit because the unit's series of clay and silt beds vary greatly in stratigraphic position. Spatial dataset pp1773_layer3_extent represents the extent of the Yorktown/Upper Floridan aquifer. The Yorktown aquifer is present only in the northern half of the North Carolina Coastal Plain. Outliers exist in Robeson, Bladen and Dublin counties, but are not separated from the surficial aquifer by a confining unit, and not considered a distinct aquifer in these areas. The Upper Floridan aquifer extent covers a southern portion of South Carolina and southern portion of Georgia. Spatial dataset pp1773_layer4_extent represents the extent of the Castle Hayne/Middle Floridan confining unit. The Castle Hayne confining unit consists of beds of clay and silt that vary in stratigraphic position and are absent in a number of areas in the central and southern North Carolina Coastal Plain. The Middle Floridan confining unit extends from South Carolina to southern Georgia. It is not continuous with the Castle Hayne confining unit. Spatial dataset pp1773_layer5_extent represents the extent of the Castle Hayne/Middle Floridan aquifer. The Castle Hayne aquifer is located in the central and southern North Carolina Coastal Plain; the Middle Floridan aquifer is more south, in southern South Carolina and southern Georgia. Spatial dataset pp1773_layer6_extent represents the extent of the Beaufort/Gordon confining unit. The Beaufort confining unit is located in northeastern North Carolina and southeastern Virginia. It is best developed in

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.