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 geochmical modeling 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 geochmical modeling results (Carbon14) contain input paramters and final gechmical models of carbon-14. Please see the processing steps below and the main manuscript for additional details on the results presented in this table.
Aeschbach-Hertig, W., Peeters, F., Beyerle, U., and Kipfer, R., 1999, Interpretation of dissolved atmospheric noble gases in natural waters: Water Resources Research, v. 35, no. 9, p. 2,779–2,792, doi: 10.1029/1999WR900130.
Jurgens, B.C., Böhlke, J.K., and Eberts, S.M., 2012, TracerLPM (Version 1): An Excel® workbook for interpreting groundwater age distributions from environmental tracer data: U.S. Geological Survey Techniques and Methods Report 4-F3, p. 60, doi:10.3133/tm4F3
Solomon, D.K., 2000, 4He in groundwater, chap. 14 of Cook, P.G., and Herczeg A.L., eds., Environmental tracers in subsurface hydrology: Boston, Kluwer Academic Publishers, p. 425–440. doi:10.1007/978-1-4615-4557-6_4.
Solomon, D.K., and Cook, P.G., 2000, 3H and 3He, chap. 13 of Cook, P.G., and Herczeg A.L., eds., Environmental tracers in subsurface hydrology: Boston, Kluwer Academic Publishers, p. 397–424. doi:10.1007/978-1-4615-4557-6_4.
Weiss, R.F., 1970, The solubility of nitrogen, oxygen and argon in water and seawater: Deep Sea Research and Oceanographic Abstracts, v. 17, n. 4., p. 721-735, doi:10.1016/0011-7471(70)90037-9.