HomeMy Public PortalAbout20110321KennedyCRC.pdf0
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 2005-5089
2
Upper Floridan Aquifer Potentiometric Surface
USGS SIR 2006-5058
3
Direction of Groundwater Movement & Salt Water Intrusion
USGS SIR 2006-5058
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
Possible Sustainable Yields
0
5
10
15
20
25
30
35
40
1 2 3 4 5 6 7 8 9
Combination Number
To
t
a
l
S
u
a
t
a
i
n
a
b
l
e
Y
i
e
l
d
(
m
g
d
)
Savannah Area Georgia Yellow Zone Hilton Head Island
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
$0
$200,000,000
$400,000,000
$600,000,000
$800,000,000
$1,000,000,000
$1,200,000,000
$1,400,000,000
$1,600,000,000
4 2 3 7 6 13 10 12 9 16 15 22 5 19 8 21 18 25 11 14 24 28 17 27 20 23 26 29 1
Aquifer Management Option Number
Co
s
t
Total Cost Georgia Cost South Carolina Cost
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 2010-5158
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 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
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