1. Groundwater Modeling in the South Carolina Coastal Plain
Bruce Campbell,
USGS – South Atlantic Water Science Center
Alex Butler and Joe Gellici
South Carolina Department of Natural Resources

2. What is a groundwater flow model?

3. Computer models of groundwater systems simulate the flow of groundwater,
producing groundwater levels and budgets
Framework on which to organize their knowledge and understanding of
groundwater systems
Groundwater models may be used to:
predict the effects of hydrological changes -- groundwater withdrawals,
irrigation developments, or climate change) on the behavior of the aquifer
2) used in various water management plans for urban and rural areas.

4. 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

5. USGS Regional Aquifer System Analysis (RASA) 1980’s
Georgia
Bob Faye and Greg Mayer
North Carolina
Gerry Geise
Ron Coble and Jodie Eimers
South Carolina
Walt Aucott and Gary Speiran

6. Mount Pleasant Waterworks – Groundwater Modeling Studies

7. Chesterfield County - Groundwater Modeling Studies

8. McBee, SC Area
Alligator Rural Water - Well Field
Simulated Groundwater Levels
Particle Tracks
Groundwater Age Dates

9. USGS Groundwater Resources Program – Started in 2004
GW Model of NC and SC Coastal Plain
Calibrated to 2004 conditions
Revised hydrogeologic framework
Analysis of GW monitoring networks
Climate change predictions

10. SC Coastal Plain Issues
Increase in Atlantic Coastal Plain population
Increased demand on groundwater resources
Groundwater quality issues
Increased agricultural withdrawals
SC Agriculture Dept recruiting industrial-scale farms
Impact of increased groundwater withdrawals on surface water flows

11. South Carolina Water Plan
South Carolina Department of Natural Resources
Recommendation:
“A comprehensive ground-water flow model
of the Coastal Plain should be developed and
used to predict the effect of future pumping
and to determine optimal well spacing's.”

12. A) South Carolina groundwater use,;
B) Reported irrigation groundwater
use, 1983 – 2013.

13. Irrigated Farm -
Aiken County

14. Irrigated farmland in Barnwell County, SC

15. USGS 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

16. SCDNR / Focus Area Study
Groundwater
Model Area
SCDNR / Focus Area Study
Model Area

17. Project Objectives Update the groundwater flow model
Activate and rediscretize 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

18. Model Scenarios Six scenarios
Will be determined by the State Cooperators
Will involve:
Additional potential future withdrawals
Climate change
Projected land use changes

19. Questions?

20. Aiken County
Groundwater
Availability
Study

21. Preliminary Soil-Water Balance (SWB) Modeling

22. ET and Recharge (year 2010) Calculated by SWB

24. 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

25. 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

26. 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

28. 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.)

29. 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

30. Aiken County Groundwater Flow Model
Numerical simulation of GW flow - MODFLOW
Can use most of hydrological data
See how data interacts
Calibrate to past conditions
Simulate future scenarios
Can be used by all interested parties

31. Model Cells – 400 ft x 400 ft

32. Simulated Water Levels - Gordon aquifer

33. Simulated Water Levels - Crouch Branch aquifer

34. Breezy Hill Water and Sewer - Service Area

35. Breezy Hill
Wellfield

36. Breezy Hill – Simulated
Groundwater Levels

37. 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.

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