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

Outline FKAA History FKAA History Saltwater Intrusion in southeast Miami- Dade County Saltwater Intrusion in southeast Miami- Dade County SWIM Monitoring Program SWIM Monitoring Program Results Results Conclusions Conclusions

Key West Claimed by the United States in 1822 Claimed by the United States in 1822 Major industries included sponging, salt, and wrecking Major industries included sponging, salt, and wrecking Largest city in Florida until 1860 Largest city in Florida until 1860 Overseas railroad completed in 1912 Overseas railroad completed in 1912

Florida Keys Aqueduct Authority Autonomous public water utility Autonomous public water utility Established in 1937 by state charter Established in 1937 by state charter Commissioned a study (1938) to identify a water-supply source for the Keys Commissioned a study (1938) to identify a water-supply source for the Keys

1938 Report Evaluated Five Water Supply Options Evaluated Five Water Supply Options –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: Recommended Source: –Groundwater from Homestead –Cost estimate: $2.94 million (€1.89 million)

The FKAA today Produces approximately 18 mgd (68,000 m 3 /d) of treated drinking water from 10 wells Produces approximately 18 mgd (68,000 m 3 /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) Treated water is pumped 130 miles (210 km) at pressures up to 250 psi (1,700 kPa) Annual budget is $55 million (€35 million) Annual budget is $55 million (€35 million) Currently constructing a $36 million (€23 million) reverse-osmosis water treatment plant to meet future demands Currently constructing a $36 million (€23 million) reverse-osmosis water treatment plant to meet future demands

Outline FKAA History FKAA History Saltwater Intrusion in southeast Miami- Dade County Saltwater Intrusion in southeast Miami- Dade County SWIM Monitoring Program SWIM Monitoring Program Results Results Conclusions Conclusions

Biscayne Aquifer Unconfined Unconfined Limestone, sand, shell Limestone, sand, shell Transmissivity up to 300,000 ft 2 /d (28,800 m 2 /d) Transmissivity up to 300,000 ft 2 /d (28,800 m 2 /d) Upper productive interval is approximately 80 ft (24 m) thick 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 Pre-development conditions First noted in the early 20 th century First noted in the early 20 th century Drainage and municipal withdrawals Drainage and municipal withdrawals

Parker et al., 1955 The drought impacted crop production in the Homestead area The drought impacted crop production in the Homestead area Identified un-controlled canals as conduits for saltwater intrusion 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 m 3 /d) without causing saline intrusion Concluded that withdrawals from the FKAA’s wellfield could be increased to 18 mgd (68,000 m 3 /d) without causing saline intrusion Used an electric analog model to evaluate additional water provided by a conveyance canal Used an electric analog model to evaluate additional water provided by a conveyance canal

from Meyer (1974)

Sonenshein, 1996 FKAA

Outline FKAA History FKAA History Saltwater Intrusion in southeast Miami- Dade County Saltwater Intrusion in southeast Miami- Dade County SWIM Monitoring Program SWIM Monitoring Program Results Results Conclusions Conclusions

Salt Water Intrusion Monitor Well Network FKAA FKAA –FKS wells USGS USGS –G wells

SWIM Monitoring Program Regulatory requirement Regulatory requirement Wells are sampled monthly; more frequently during droughts Wells are sampled monthly; more frequently during droughts Water levels Water levels Chloride Chloride Conductivity Conductivity

SWIM Well Construction FKAA wells FKAA wells –6-8 inch (15-20 cm) diameter borehole –Several 1-2 inch (3-5 cm) diameter PVC sampling tubes USGS wells USGS wells –2-inch (5 cm) PVC casing –relatively small open interval at bottom of each well

Shallow and Deep Horizons 26 m

Outline FKAA History FKAA History Saltwater Intrusion in southeast Miami- Dade County Saltwater Intrusion in southeast Miami- Dade County SWIM Monitoring Program SWIM Monitoring Program Results Results Conclusions Conclusions

Saline Interface 250 mg/L chloride contour 250 mg/L chloride contour –Regulatory definition of saline water Contour line position interpolated using SURFER’s multiquadratic radial basis function algorithm Contour line position interpolated using SURFER’s multiquadratic radial basis function algorithm Annual average contour line interpolated for shallow and deep intervals Annual average contour line interpolated for shallow and deep intervals

Shallow Wells ft bls (11-14 m) 250 mg/L interface remains relatively stable from 1996 to mg/L interface remains relatively stable from 1996 to 2003 Wells FKS-7, - 8, and -9 installed in 2004 Wells FKS-7, - 8, and -9 installed in

(11 m)

Deep (55 to 65 ft) (17 to 20 m) Advances between 1996 and 1998 Advances between 1996 and 1998 Retreats between 1999 and 2001 Retreats between 1999 and 2001

Well G-1264 goes salty Well G-1264 goes salty Severe drought in 2001 Severe drought in 2001 Deep (55 to 65 ft) (17 to 20 m)

(18-20 m)

Relatively stable interface Relatively stable interface Deep (55 to 65 ft) (17 to 20 m)

Driving Forces Climatic Climatic –Droughts in 2001, 2004 and 2006/2007 Increased groundwater withdrawals in the South Dade area Increased groundwater withdrawals in the South Dade area Canal level management Canal level management

Outline FKAA History FKAA History Saltwater Intrusion in southeast Miami- Dade County Saltwater Intrusion in southeast Miami- Dade County SWIM Monitoring Program SWIM Monitoring Program Results Results Conclusions Conclusions

Conclusions Continued monitoring necessary to provide advance warning of saltwater intrusion Continued monitoring necessary to provide advance warning of saltwater intrusion The saltwater front “jumps” rather than “creeps” The saltwater front “jumps” rather than “creeps” –Drought –Hurricanes

Recommendations Future monitoring wells should be completed to the base of the aquifer Future monitoring wells should be completed to the base of the aquifer Multi-zone monitoring wells should be replaced with discrete-interval wells Multi-zone monitoring wells should be replaced with discrete-interval wells Downhole logging of existing wells Downhole logging of existing wells –flow –geophysical Geochemical analysis Geochemical analysis –relict seawater vs. recent seawater

Acknowledgements Florida Keys Aqueduct Authority Florida Keys Aqueduct Authority -Jolynn Reynolds -SWIM sampling crew USGS USGS –Scott Prinos

Image from sunsetcelebration.org