DOI: 10.5066/p9jbqmcw
title: Data for Assessing the Susceptibility of Groundwater Using Environmental Tracers in Northern Atlantic Coastal Plain Aquifer System and Piedmont and Blue Ridge Crystalline-Rock Aquifers of Eastern United States

description: 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.