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Simulation of Groundwater Flow in Wake County, North Carolina, 2000 Through 2070

Scientific Investigations Report 2025-5087
Prepared in cooperation with Wake County Environmental Services
By: , , and 
https://doi.org/10.3133/sir20255087

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Abstract

In 2019, the U.S. Geological Survey and Wake County Environmental Services began a collaborative study to evaluate groundwater resources and long-term groundwater availability in the county’s fractured-rock groundwater system. Wake County, in central North Carolina, is experiencing rapid population growth, associated land development, and changing water use. Hydrogeologic data including groundwater levels, aquifer testing, borehole fracture flow measurements, water-quality samples, and groundwater age-dating tracers were collected, along with findings from previous investigations, to help inform a conceptual model of the flow system used to develop a modular three-dimensional finite-difference groundwater-flow model (MODFLOW) for simulating historical and future groundwater conditions from 2000 to 2070.

Hydraulic conductivity and transmissivity ranges were estimated from 17 slug tests and 21 borehole-flow measurements. Groundwater-quality analytical results from 19 sampling sites indicate that oxidation-reduction (redox) conditions varied within the regolith and bedrock and that minimal evaporation occurred before recharge entered the groundwater system. Age dating revealed mixtures of older and younger water, ranging from the 1940s to the 1990s—indicating variable flow pathways of recharge within permeable bedrock fracture zones.

To simplify the complex fractured-rock groundwater system, two layers representing the regolith and the fractured bedrock were used in the MODFLOW model. Model calibration included parameter estimation and provided a reasonable fit to observed groundwater levels and estimated stream base flows. The model forecast scenarios incorporated future climate-model data for two emissions scenarios with land cover change projections to simulate potential impacts to future groundwater levels, recharge, and base flows. Recharge and base flow projections were largely within historical ranges, with no apparent long-term trends, but did indicate a slight downward shift in median values—likely, in part, because of differences in spatial resolution of input climate datasets. Seasonal patterns were consistent with historical data, with projections of possible increases in future winter recharge. Model limitations are discussed, and additional monitoring and model refinement needs are highlighted to support decision making for local groundwater management.

Suggested Citation

Antolino, D.J., Gonthier, G.J., and Sanchez, G.M., 2025, Simulation of groundwater flow in Wake County, North Carolina, 2000 through 2070: U.S. Geological Survey Scientific Investigations Report 2025–5087, 77 p., https://doi.org/10.3133/sir20255087.

ISSN: 2328-0328 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Abstract
  • Introduction
  • Methods
  • Characterization of Aquifer Hydraulic Properties
  • Groundwater Geochemistry
  • Evaluation of Model Calibration and Performance
  • Model Limitations and Future Considerations
  • Summary
  • References Cited
  • Appendix 1. Summary of Percentile Data for Recharge and Base Flow Simulations for Calibrated and Forecast Periods for a Groundwater Model in Wake County, North Carolina
Publication type Report
Publication Subtype USGS Numbered Series
Title Simulation of groundwater flow in Wake County, North Carolina, 2000 through 2070
Series title Scientific Investigations Report
Series number 2025-5087
DOI 10.3133/sir20255087
Publication Date December 03, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) South Atlantic Water Science Center
Description Report: xii, 77 p.; 2 Data Releases
Country United States
State North Carolina
County Wake County
Online Only (Y/N) Y
Additional publication details