Transcript Saltwater Intrusion Monitoring in the Biscayne Aquifer near Florida City, Miami-Dade County, Florida: 1996-2007 Chris Peters CH2M HILL Deerfield Beach, FL, USA Jolynn Reynolds Florida Keys Aqueduct Authority Key.

Saltwater Intrusion Monitoring
in the Biscayne Aquifer
near Florida City, Miami-Dade
County, Florida: 1996-2007
Chris Peters
CH2M HILL
Deerfield Beach, FL, USA
Jolynn Reynolds
Florida Keys Aqueduct Authority
Key West, FL, USA
Key West
• Claimed by the United States in 1822
• Major industries included sponging, salt,
and wrecking
• Largest city in Florida until 1860
• Overseas railroad completed in 1912
Florida Keys Aqueduct Authority
• Autonomous public water utility
• Established in 1937 by state charter
• Commissioned a study (1938) to identify a
water-supply source for the Keys
1938 Report
• Evaluated Five Water Supply Options
–
–
–
–
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Surface water supply in the Keys
Shallow wells or infiltration galleries in the Keys
Deep well supply
Solar distillation
Hauling water from the mainland
• Recommended Source:
– Groundwater from Homestead
– Cost estimate: $2.94 million (€1.89 million)
The FKAA today
• Produces approximately 18 mgd (68,000 m3/d)
•
•
•
of treated drinking water from 10 wells
Treated water is pumped 130 miles (210 km) at
pressures up to 250 psi (1,700 kPa)
Annual budget is $55 million (€35 million)
Currently constructing a $36 million (€23 million)
reverse-osmosis water treatment plant to meet
future demands
Biscayne Aquifer
• Unconfined
• Limestone, sand, shell
• Transmissivity up to 300,000 ft2/d
(28,800 m2/d)
• Upper productive interval is approximately
80 ft (24 m) thick
Conceptual Cross-Section of the
Biscayne Aquifer
Image from Fish and Stewart (1991)
Saltwater Intrusion in Southeast
Miami-Dade County
• Pre-development conditions
• First noted in the early 20th century
• Drainage and municipal withdrawals
Parker et al., 1955
• The 1943-1945 drought impacted crop
production in the Homestead area
• Identified un-controlled canals as conduits
for saltwater intrusion
Meyer, 1974
• Concluded that withdrawals from the
FKAA’s wellfield could be increased to 18
mgd (68,000 m3/d) without causing saline
intrusion
• Used an electric analog model to evaluate
additional water provided by a conveyance
canal
from Meyer (1974)
Sonenshein, 1996
FKAA
Salt
Water
Intrusion
Monitor
Well
Network
• FKAA
– FKS wells
• USGS
– G wells
SWIM Monitoring Program
• Regulatory requirement
• Wells are sampled monthly; more
frequently during droughts
• Water levels
• Chloride
• Conductivity
SWIM Well Construction
• FKAA wells
– 6-8 inch (15-20 cm) diameter borehole
– Several 1-2 inch (3-5 cm) diameter PVC
sampling tubes
• USGS wells
– 2-inch (5 cm) PVC casing
– relatively small open interval at bottom of
each well
Shallow and Deep Horizons
Depth, ft bls
0
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
FKS-1
FKS-2
FKS-3
FKS-4
FKS-5
FKS-6
FKS-7
FKS-8
26 m
Depth, ft bls
1251
0
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85 26 m
1264
1603
3164
3166
3167
3342
FKS-9
Saline Interface
• 250 mg/L chloride contour
– Regulatory definition of saline water
• Contour line position interpolated using
SURFER’s multiquadratic radial basis
function algorithm
• Annual average contour line interpolated
for shallow and deep intervals
Shallow Wells
35-45 ft bls
(11-14 m)
• 250 mg/L
interface
remains
relatively
stable from
1996 to 2003
• Wells FKS-7, 8, and -9
installed in
2004
1996-2003
FKS-7, 8, and 9
Chloride Concentration
35 ft bls
(11 m)
Chloride concentration, mg/L
80
70
60
50
40
30
20
10
0
Jan-04
Jan-06
Jan-08
Date
FKS-8 (Shallow)
FKS-9 (Shallow)
FKS-7 (Shallow)
Deep (55 to 65 ft)
(17 to 20 m)
1996-2001
• Advances
between 1996
and 1998
• Retreats
between 1999
and 2001
Deep (55 to 65 ft)
(17 to 20 m)
2002-2003
• Well G-1264
goes salty
• Severe
drought in
2001
G-1264 Chloride Concentration
60-65 ft bls
Chloride concentration, mg/L
3500
(18-20 m)
3000
2500
2000
1500
1000
500
0
Jan-90 Jan-92 Jan-94 Jan-96 Jan-98 Jan-00 Jan-02 Jan-04 Jan-06 Jan-08 Jan-10
Date
Deep (55 to 65 ft)
(17 to 20 m)
2004-2007
• Relatively
stable
interface
Driving Forces
• Climatic
– Droughts in 2001, 2004 and 2006/2007
• Increased groundwater withdrawals in the
South Dade area
• Canal level management
Annual Public Supply Groundwater Withdrawals (MG)
70
35
60
30
50
25
40
20
30
Pumpage
Rainfall
15
10
1998
20
2000
2002
2004
2006
10
2008
Annual Rainfall (inches)
40
Conclusions
• Continued monitoring necessary to
provide advance warning of saltwater
intrusion
• The saltwater front “jumps” rather than
“creeps”
– Drought
– Hurricanes
Recommendations
• Future monitoring wells should be completed to
•
•
the base of the aquifer
Multi-zone monitoring wells should be replaced
with discrete-interval wells
Downhole logging of existing wells
– flow
– geophysical
• Geochemical analysis
– relict seawater vs. recent seawater
Acknowledgements
• Florida Keys Aqueduct Authority
- Jolynn Reynolds
- SWIM sampling crew
• USGS
– Scott Prinos
Image from sunsetcelebration.org