1. Development and Application of a Groundwater-Flow Model of the Atlantic Coastal Plain aquifers, Aiken County, South Carolina to Support Water Resource Decisions
Bruce Campbell and Jim Landmeyer
USGS – South Atlantic Water Science Center
Alex Butler and Joe Gellici
South Carolina Department of Natural Resources

2. Aiken County
Groundwater
Availability
Study

3. Aiken County Groundwater Resources
Heavy reliance on groundwater
Pumped primarily from Atlantic Coastal Plain sediments / aquifers
Upper Coastal Plain – Fall Line
Underlain by multiple aquifers
Generally - very dilute water

4. Aiken County Groundwater Use - 2010
Total - about 14 Million Gallons per Day
City of Aiken – about 7 MGD
One of the largest users of groundwater in SC
All public water utilities in county except one use primarily a groundwater source
Irrigation use - increasing

5. Irrigation Water Use in Aiken County
Recent siting of several “industrial” scale farms of 5,000+ acres
Significant increase in water use – both surface and groundwater
At least 2 more large scale farms are being sited
Local concern over impact on water resources and existing users
Have had lots of interest in the on-going project.
County has requested state regulation of groundwater withdrawals

6. Approach Collect data and interpret
Construct groundwater-flow model of Aiken County
Determine the water budget
Determine “Capture Zones” for existing and planned PSWs
Determine age of groundwater to assess vulnerability and availability
Comprehensive water-quality analyses (VOCs, radionuclides, iron, etc.)

7. Benefits to Aiken County
Determine availability of groundwater for future use
Coordinate planning among Aiken County groundwater users
Provide SC Dept of Health and Environmental Control with data and information for potential Capacity Use designation
A Management tool

8. Calibration Strategy Have groundwater levels from over 2,100 wells
Groundwater baseflow data at 13 existing and past stream gages
Discrete stream flow measurements
Continuous groundwater levels at 19 wells
Steady state and transient model

9. Model Cells – 400 ft x 400 ft

10. Simulated Water Levels - Gordon aquifer

11. Simulated Water Levels - Crouch Branch aquifer

12. Breezy Hill Water and Sewer - Service Area

13. Breezy Hill
Wellfield

14. Breezy Hill – Simulated
Groundwater Levels

15. Model Scenarios
Base Case: A “base case” simulation will be established that will comprise of pumping existing wells at their reported 2015 withdrawal rates out to year 2050.
Base Case Plus 0.5-percent Annual Increase: The 2015 withdrawal rates will be increased by 0.5 percent per annum to 2050, for a cumulative increase of 8 percent.
Drought: The effect of a 10-year drought will be simulated for the years by reducing the annual average recharge rates by 5 to 10 percent and simulating the “base case” pumping rates.
Agricultural Withdrawals Increase: Using Scenario (2), the effect of withdrawals by anticipated increases in agricultural pumping in the County will be simulated by adding 20 new irrigation wells in the study area.

16. So what!?
How does that
help me manage groundwater
resources?

17. Groundwater Management Topics
Groundwater – surface water interactions
Groundwater budgets
Groundwater management
All can be done with groundwater flow models

18. Groundwater – surface water interactions
Gaining Stream – Groundwater is
discharging to the stream, streamflow
tends to increase down stream
Losing Stream – Surface water is
moving vertically through the
stream bed and recharging the
groundwater.

19. Groundwater – surface water interactions
Effects of pumping from a hypothetical
water-table aquifer that discharges
to a stream.
The pumping rate of the well may be large
enough to cause water to flow from
the stream to the aquifer

20. Groundwater Budgets
Provide a means for evaluating availability and sustainability of a water supply,
Rate of change in water stored in an area, such as an aquifer or part of an
aquifer, is balanced by the rate at which water flows into and out of the area,
Foundation for effective water-resource and environmental
planning and management.
Observed changes in water budgets of an area over time can be used to
assess the effects of climate variability and human activities on water resources.

21. Groundwater Budget
Components

23. Groundwater Management
practices include the engineering,
economic, and political factors,
Affect the locations, rates, and
timing of imposed hydrologic
stresses to the ground-water system
Imposed hydrologic stresses then
affect the responses, or outputs,
of the ground-water system

24. Questions? USGS Publications on these topics and many others:
Questions?

25. Questions?

26. Representative GW Flow Model
Primary inputs:
- Model Grid
- Hydrogeologic Framework
- Aquifer Properties
- Observation Data
- Boundaries
- Wells – Water Use Data
Primary Outputs:
- Groundwater Levels
- Budgets
Representative GW Flow Model

27. Current Groundwater Modeling Projects –
Focus Area Study / Model Update
Aiken County

28. Focus Area Study / SCDNR Model Update
Combines funding sources:
Internal USGS Water Census Program / Focus Area Study
Cooperative funding from South Carolina Department of Natural Resources/USACOE
1) Water Census Program / Focus Area Study:
Internal USGS funding from the SECURE Water Act
Southeastern Atlantic Coastal Basins of the Carolinas
2) SCDNR/US ACOE Project
Funding to expand groundwater model area to include
all of the SC Coastal Plain

29. Groundwater
Model Area
Model Area

30. Project Objectives Update the groundwater flow model
Activating and rediscretizing the surficial aquifer model layer
Adding recent groundwater-related data ( )
Refine the model grid in some areas
Incorporate a more detailed representation of the Fall Line area
Incorporate new MODFLOW packages – Newton Formulation, Multi-Node Well Package, etc
Variable-density offshore boundary
Re-calibration, and apply the model to a series of 6 scenarios