Groundwater Age and Susceptibility of South Atlantic and Gulf Coast Principal Aquifers of the Contiguous United States

Scientific Investigations Report 2020-5050
National Water-Quality Program
National Water-Quality Assessment Project


  • Document: Report (4.5 MB pdf)
  • Data Release: Data Release - Data for groundwater age and susceptibility of poorly consolidated sedimentary aquifers of the United States Gulf Coast: Results from the Southeast Coastal Plain (SECP), Coastal Lowland (CLOW), Mississippi Embayment and Texas Coastal Upland (METX) Principal Aquifer Networks
  • Open Access Version: Publisher Index Page
  • Download citation as: RIS | Dublin Core


Groundwater susceptibility to contamination was investigated by using environmental tracer-based groundwater age metrics in the south Atlantic and Gulf Coast principal aquifer systems of the Southeastern Coastal Plain, Mississippi embayment–Texas coastal uplands, and the Coastal Lowlands. Samples of dissolved gas, tritium, sulfur hexafluoride, tritiogenic helium, and carbon-14 were collected from 231 public supply wells in the 3 principal aquifer systems. Dissolved gas models were used to characterize recharge conditions and they identified recharge mechanisms that ranged from rapid, but short-lived, water table rises (possibly associated with large scale flooding), to slower diffuse recharge not associated with large water table fluctuations. Dissolved gas and geochemical correction models were used to calculate and (or) correct tracer concentrations before input to lumped parameter models of groundwater age. Lumped parameter models that were fit to tracer concentrations indicated groundwater was relatively old across the aquifer systems, with an estimated mean age of about 30,000 years. Estimates of groundwater age were related to hydrogeology, with increasing groundwater ages associated with greater depth, confinement, and distance from the recharge zone. Young groundwater with mean ages less than 2,000 years generally was in unconfined parts of the aquifer system, except for local areas of heavy groundwater extraction from unconfined aquifer units where estimated mean ages were up to 15,000 years. Lumped parameter model optimized age distributions describe the relative contribution of differing flow paths to the mean age, and a composite distribution of all samples from the three aquifer systems indicated that about 15 percent of the total sampled water had an age of less than 100 years. Various metrics of susceptibility, to land surface and geogenic contamination sources, derived from the age distributions, indicated geogenic sources as the primary threat to groundwater quality in the aquifer systems. Values of the susceptibility index (unitless) and fraction of recharge since 2,000 and 15,000 years before present are provided for assessment of individual well susceptibility. The data and interpretation methods presented here provide an additional means of investigating the susceptibility and sustainability of groundwater resources of the Southeastern Coastal Plain, Mississippi embayment–Texas coastal uplands, and the Coastal Lowlands aquifer systems.

Suggested Citation

Solder, J.E., 2020, Groundwater age and susceptibility of south Atlantic and Gulf Coast principal aquifers of the contiguous United States: U.S. Geological Survey Scientific Investigations Report 2020–5050, 46 p.,

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Hydrogeology
  • Methods
  • Results
  • Discussion and Summary of Important Findings
  • Conclusion
  • References Cited

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Groundwater age and susceptibility of south Atlantic and Gulf Coast principal aquifers of the contiguous United States
Series title Scientific Investigations Report
Series number 2020-5050
DOI 10.3133/sir20205050
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Utah Water Science Center
Description Report: vi, 46 p.; Data Release
Country United States
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional metadata about this publication, not found in other parts of the page is in this table