HomeMy Public PortalAbout20110321KennedyCRC.ppt
Modeling of
Salt-Water Intrusion
James L. Kennedy, Ph.D., P.G.
Georgia Environmental Protection Division
State Geologist
Aquifers in coastal Georgia include the surficial aquifer and, at increasing depths, the Brunswick aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer. Aquifers
are separated by confining units.
Aquifers in Coastal Georgia
USGS SIR 2005-5089
Aquifers in coastal Georgia include the surficial aquifer and, at increasing depths, the Brunswick aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer. Aquifers
are separated by confining units.
Upper Floridan Aquifer Potentiometric Surface
USGS SIR 2006-5058
Before pumping of the Upper Floridan aquifer started in the 1880s the direction of groundwater movement was toward port Royal Sound and the Atlantic Ocean and groundwater from the aquifer
discharged to the sound and ocean. Pumping of the Upper Flordidan aquifer resulted in a cone of depression that is centered in Savannah, Georgia. Groundwater movement is now toward
the center of the cone of depression.
Direction of Groundwater Movement & Salt Water Intrusion
USGS SIR 2006-5058
Before pumping of the aquifer started groundwater discharged to Port Royal Sound sound and the Atlantic Ocean by leakage through the onfining unit or by discharge from underwater springs.
Pumping of the Upper Flordidan aquifer caused salt water to move from the sound and ocean into the aquifer.
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
South Carolina Department of Health and Environmental Control (DHEC) provided information on the extent of measured salt water plumes during 2007. The plumes were larger than those
observed during 2003 and different than those generated by the USGS modeling. Compared to the plume modeled by USGS the measured plume extended further south on northeastern Hilton
Head Island and did not extend as far south or on to the island south of Pinckney Island.
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
The refined model adequately simulated the 2007 chloride contours provided by South Carolina DHEC. This was the starting point for management scenario simulations.
Groundwater Withdrawals That Stop Plume Movement
Aquifers in coastal Georgia include the surficial aquifer and, at increasing depths, the Brunswick aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer. Aquifers
are separated by confining units.
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
The refined model was used to simulate a theoretical salt water plume with historical pumping in the Savannah area only and no pumping on Hilton Head Island. The plume boundary closely
matched the measured 2007 plume boundary on the northern side of Port Royal Sound and southwest of the Colleton River. The theoretical historical plume did not extend as far inland
on the northern end of the island as the measured 2007 plume boundary.
Salt-Water Plumes Would Continue to Exist Even With No Withdrawals
The refined model was used to simulate aquifer management scenarios that included overall percentages of pumping reductions in the Savannah area and on Hilton Head Island. The percentages
of reduction were from the 69 million gallons per day (MGD) withdrawn from the Savannah area during 2000 and the 9 MGD withdrawn from Hilton Head Iisland during 2007. The 2000 data
for the Savannah area were the most complete on pumping locations and rates for input to the model nodes and the 69 MGD withdrawal was close to the withdrawal during 2007. The 2000
withdrawal from Hilton Head Island was on the order of about 14 MGD and could have caused the model to overly predict effects of pumping on Hilton Head Island. Initial model runs also
included scenarios with reductions of 50% in the Savannah area and 20% on Hilton Head Island, 20% in the Savannah area and 50% on Hilton Head Island, and 20% in the Savannah area and
on Hilton Head Island. The simulations showed results similar to those listed above and were not repeated in the final scenario simulations.
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
After calibration the Technical Advisory Committee (TAC) considered the refined model to be useable for simulating aquifer management scenarios. The TAC included members from South
Carolina DHEC, South Carolina Department of Natural Resources, consultants to DHEC, and Georgia Environmental Protection Division.
Downward Migration of Salt Water Through the Upper Confining Unit
The refined model was used to simulate aquifer management scenarios that included overall percentages of pumping reductions in the Savannah area and on Hilton Head Island. The percentages
of reduction were from the 69 million gallons per day (MGD) withdrawn from the Savannah area during 2000 and the 9 MGD withdrawn from Hilton Head Iisland during 2007. The 2000 data
for the Savannah area were the most complete on pumping locations and rates for input to the model nodes and the 69 MGD withdrawal was close to the withdrawal during 2007. The 2000
withdrawal from Hilton Head Island was on the order of about 14 MGD and could have caused the model to overly predict effects of pumping on Hilton Head Island. Initial model runs also
included scenarios with reductions of 50% in the Savannah area and 20% on Hilton Head Island, 20% in the Savannah area and 50% on Hilton Head Island, and 20% in the Savannah area and
on Hilton Head Island. The simulations showed results similar to those listed above and were not repeated in the final scenario simulations.
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
The refined model was used to simulate aquifer management scenarios that included overall percentages of pumping reductions in the Savannah area and on Hilton Head Island. The percentages
of reduction were from the 69 million gallons per day (MGD) withdrawn from the Savannah area during 2000 and the 9 MGD withdrawn from Hilton Head Iisland during 2007. The 2000 data
for the Savannah area were the most complete on pumping locations and rates for input to the model nodes and the 69 MGD withdrawal was close to the withdrawal during 2007. The 2000
withdrawal from Hilton Head Island was on the order of about 14 MGD and could have caused the model to overly predict effects of pumping on Hilton Head Island. Initial model runs also
included scenarios with reductions of 50% in the Savannah area and 20% on Hilton Head Island, 20% in the Savannah area and 50% on Hilton Head Island, and 20% in the Savannah area and
on Hilton Head Island. The simulations showed results similar to those listed above and were not repeated in the final scenario simulations.
Simulated Effects of SHEP Dredging on Aquifer Chloride
No SHEP Dredging
SHEP Dredging
SHEP: Savannah Harbor Expansion Project
South Carolina Department of Health and Environmental Control (DHEC) provided information on the extent of measured salt water plumes during 2007. The plumes were larger than those
observed during 2003 and different than those generated by the USGS modeling. Compared to the plume modeled by USGS the measured plume extended further south on northeastern Hilton
Head Island and did not extend as far south or on to the island south of Pinckney Island.
Simulated Chloride at Tybee Island Well 025M0602
South Carolina Department of Health and Environmental Control (DHEC) provided information on the extent of measured salt water plumes during 2007. The plumes were larger than those
observed during 2003 and different than those generated by the USGS modeling. Compared to the plume modeled by USGS the measured plume extended further south on northeastern Hilton
Head Island and did not extend as far south or on to the island south of Pinckney Island.
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
Aquifers in coastal Georgia include the surficial aquifer and, at increasing depths, the Brunswick aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer. Aquifers
are separated by confining units.
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
Before pumping of the Upper Floridan aquifer started in the 1880s the direction of groundwater movement was toward port Royal Sound and the Atlantic Ocean and groundwater from the aquifer
discharged to the sound and ocean. Pumping of the Upper Flordidan aquifer resulted in a cone of depression that is centered in Savannah, Georgia. Groundwater movement is now toward
the center of the cone of depression.
Lower Floridan Aquifer as an Alternate Source of Water
USGS SIR 2010-5158
Aquifers in coastal Georgia include the surficial aquifer and, at increasing depths, the Brunswick aquifer system, the Upper Floridan aquifer, and the Lower Floridan aquifer. Aquifers
are separated by confining units.
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 2010-5158
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
After calibration the Technical Advisory Committee (TAC) considered the refined model to be useable for simulating aquifer management scenarios. The TAC included members from South
Carolina DHEC, South Carolina Department of Natural Resources, consultants to DHEC, and Georgia Environmental Protection Division.
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
After calibration the Technical Advisory Committee (TAC) considered the refined model to be useable for simulating aquifer management scenarios. The TAC included members from South
Carolina DHEC, South Carolina Department of Natural Resources, consultants to DHEC, and Georgia Environmental Protection Division.