0 Modeling of Salt-Water Intrusion James L. Kennedy, Ph.D., P.G. Georgia Environmental Protection Division State Geologist

1 Aquifers in Coastal Georgia USGS SIR

2 Upper Floridan Aquifer Potentiometric Surface USGS SIR

3 Direction of Groundwater Movement & Salt Water Intrusion USGS SIR

4 SCDHEC 2007 Chloride Contours vs. Simulated 2007 Chloride Contours SCDHEC Contours Simulated Contours The model was considered to be adequately calibrated because simulated water levels closely matched water levels measured in wells and the model closely simulated when the salt water plume arrived at wells and the range of chloride concentrations at the well

5 Reducing Withdrawals Would Not Eliminate Salt-Water Intrusion 30 Years of Pumping with No Reductions in Savannah Area or Hilton Head Island Withdrawals (about 69 mgd in the Savannah area and 9 mgd on Hilton Head Island) After 30 Years of Pumping with 50% Reductions in Savannah Area and Hilton Head Island Withdrawals the Simulated Plume Still Moves Inland

6 Groundwater Withdrawals That Stop Plume Movement

7 Withdrawals in Savannah and HHI Were Needed to Create the Plume Historical Pumping in the Savannah Area with No Pumping on Hilton Head Island Historical Pumping on Hilton Head Island with No Pumping in the Savannah Area

8 Salt-Water Plumes Would Continue to Exist Even With No Withdrawals

9 Results of Salt-Water Intrusion Modeling The salt water intrusion model can be adequately calibrated to use for simulation of aquifer management scenarios Reducing groundwater withdrawals from the aquifer, even by large amounts, would not eliminate salt-water intrusion into the Upper Floridan aquifer Groundwater withdrawals in both the Savannah area and on Hilton Head Island were needed to create the inland extent of the current salt water plume on Hilton Head Island Salt-water plumes would continue to exist well into the future even if all groundwater withdrawals were eliminated

10 Downward Migration of Salt Water Through the Upper Confining Unit

11 Simulated Regional Downward Migration of Salt Water 2050 Salt Water at the Top of the Upper Floridan Aquifer 2050 Salt Water Midway Through the Confining Unit

12 Simulated Effects of SHEP Dredging on Aquifer Chloride No SHEP Dredging SHEP Dredging SHEP: Savannah Harbor Expansion Project

13 Simulated Chloride at Tybee Island Well 025M0602

14 40-Year Order-of-Magnitude Cost Estimates Different Options for Managing the Upper Floridan Aquifer for Salt Water Intrusion Including Combinations of Groundwater Withdrawal Reductions of 0% to 10%, Savannah are injection of 0 mgd to 10 mgd, and hydraulic extraction or injection barriers on Hilton Head Island

15 With No Withdrawal Reduction and Extraction at About 13.7 MGD Particles Do Not Break Through the Line of Extraction Wells Showing that the Salt Water Plume Would Be Captured Simulate Extraction Wells to Capture the Salt Water Plume With No Withdrawal Reduction and Extraction at About 11.3 MGD Particles (red) Break Through the Line of Extraction Wells Showing that the Salt Water Plume Would Not Be Captured

16 Lower Floridan Aquifer as an Alternate Source of Water USGS SIR

17 Protocol for Development of the Lower Floridan Aquifer Demonstrate that the Lower Floridan aquifer well is not open to the Upper Floridan aquifer as defined by USGS SIR Field test hydraulic properties of the Upper Floridan aquifer, Lower Floridan aquifer, and Lower Floridan aquifer confining unit in accordance with the Georgia EPD January 2003 hydrogeological study protocol Develop a groundwater model to simulate the equivalent Upper Floridan aquifer pumping that induces the identical maximum drawdown in the Upper Floridan aquifer that would be expected as a result of pumping the Lower Floridan aquifer

18 Considerations for Development of the Lower Floridan Aquifer Limited information on the Lower Floridan aquifer at Tybee Island requires site-specific testing Lower Floridan aquifer well yield may be low Water quality may require treatment Possible high costs for field testing of Lower Floridan aquifer well yield, water quality, and aquifer hydraulic properties; and for development of groundwater model to simulate Upper Floridan aquifer drawdowns caused by Lower Floridan aquifer pumping Reduction of Upper Floridan aquifer pumping to offset drawdown caused by Lower Floridan aquifer pumping may be high