hilton head water supply saltwater intrusion files/island psds county council presentation.pdf ·...
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HILTON HEAD WATER SUPPLY
&SALTWATER INTRUSION
Beaufort County Council September 2012
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HILTON HEAD’S WATER UTILITIES
• Three public water, wastewater, reused water utilities on Hilton Head
• Formerly, 10 different utilities on island
• Result of private development
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HILTON HEAD PSD
• 18,000 customers
• 4 water sources o Reverse Osmosis
- Middle Floridan Aquifero Wholesale surface water o Upper Floridan Aquifer o Reused water
• Aquifer Storage & Recovery (ASR) well
• Peak demand of 11 million gallons
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BROAD CREEK PSD
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• 5,000 customers
• 3 water sourceso Upper Floridan
Aquifero Wholesale surface
watero Reused water
• Peak demand of 4 million gallons
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SOUTH ISLAND PSD
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• 25,000 customers
• 3 water sourceso Upper Floridan Aquifero Reverse Osmosis
- Cretaceous Aquifero Reused water
• 2 Aquifer Storage & Recovery (ASR) wells (under construction)
• Peak demand of 8.5 million gallons
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ISLAND PSDS’ REUSED WATER
• Hilton Head Island = 100% Reused Watero Golf course irrigationo Wetlands nourishment
• Together, we recycle over 2.5 billion gal./year!
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SALTWATER INTRUSION
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Aquifers and Confining Layers in the Hilton Head Island Area
Feet Below Mean Sea Level
0
100
200
300
400
500
600
Surficial Aquifer – Sand and Clay
Hawthorn Confining Layer ‐ Clay
Upper Floridan Aquifer – Permeable Limestone (under Capacity Use Area restrictions)
Middle Semi‐Confining Unit – Less Permeable Limestone
Middle Floridan Aquifer – Permeable Limestone
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UPPER FLORIDAN AQUIFER
• One of the largest aquifers in the worldo Coastal Carolinas to the Florida Everglades
• Our original source of water
• Inexpensive
• Little treatment required
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Upper Floridan Aquifer well house
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Pre-pumping Equipotential Map of the Upper Floridan Aquifer in South Carolina
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Cone of Depression in
the Upper Floridan Aquifer
Associated with
Withdrawals at Savannah
Adapted from Smith, 1998
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• Caused by overpumping in Savannah region
• Nothing the island can do to stop saltwater intrusion
• Saltwater intrusion is accelerating – 400 ft. or more a year
• Ultimately, all Upper Floridan Wells on Hilton Head will be lost to the intrusion
SALTWATER INTRUSION
USGS Conceptual Model
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SALTWATER INTRUSION
• A regional issue (GA/SC)
• More than $20 million spent on studies/models alone
• Joint stakeholder committee between the two states
Result?
• The Upper Floridan is being mined!
• Without curtailment, this natural resource will be destroyed forever
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A LONG-TERM PROBLEM
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• GA/SC will need to cut withdrawals by 80%
• Studies show all Upper Floridan wells on Hilton Head will eventually be impacted by saltwater intrusion
• Saltwater intrusion is forever – more than 300 years to recede
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THE ISLAND’S RESPONSE
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• Reduced pumping by more than 40%
• Reused water
• Efficiency/conservation customer education
• Islandwide irrigation ordinance
• Capital projects to replace lost supply
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HILTON HEAD PSD UPPER FLORIDAN
WELLS
• 6 lost to saltwater intrusion since 2000
• 5 of remaining 6 slated to be lost by 2024
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SALTWATER INTRUSION TIMELINE
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• (1995) S.C. DHEC declares capacity use zone
• (1999) Pipeline provides surface water from mainland
• (2000) PSD begins losing wells
• (2004-2006) Feasibility studies
• (2009) Opened RO Plant
• (2011) Built ASR Well
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SOUTH ISLAND PSD
• Recently discovered high chloride levels in the Long Cove Potable Well #1 have resulted in the well being removed from service.
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FINANCIAL IMPACT ON HILTON HEAD RATE/TAXPAYERS
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SALTWATER INTRUSION COSTS
• $77 million spent by Hilton Head PSD fighting saltwater intrusion
o Capitalo Operationso Debt Serviceo Purchased Water ($16.7 million)
• $20 million spent by Broad Creek PSD
• $32 million spent by South Island PSDo Supplemental water supply – Reverse Osmosis planto 2 Aquifer Storage & Recovery wells under
construction
• $129 million spent by Hilton Head, South Island, and Broad Creek PSDs combined
Since 1998…
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SALTWATER INTRUSION COSTS
In the next 20 years …
• $50 million potential to be spent by Hilton Head PSD
o Capitalo Operationso Debt Serviceo Purchased Water
• $25 million projected capital costs for South Island PSD through 2025
• $5 million potential to be spent by Broad Creek PSD
• $80 million potential to be spent by Hilton Head, South Island, and Broad Creek PSDs combined
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GOING IT ALONE
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• No state or federal funds have been used to cover these saltwater-intrusion related costs
• Solely borne by Hilton Head Island rate/taxpayers
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CAPITAL PROJECTS NEEDED TO REPLACE
LOST SUPPLY
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HILTON HEAD PSD RO PLANT
• 3 MGD
• 6 MGD potential
• Middle Floridan Aquifer, brackish
• 3 raw water wells, 600 ft. deep
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WHAT IS AQUIFER STORAGE & RECOVERY?
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• Store treated water in the underground aquifer during times of low demand
• Withdraw and retreat during times of high or peak demand
• A water storage technique; not a new source of water
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Aquifer Storage & Recovery Well
Confining Layer Confining Layer
NativeGroundwater
BufferZone Stored
WaterStored Water
Buffer Zone
Native Groundwater
Confining Layer 27
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• Built in Fall 2011• $2.5 million• 2 MGD in summer• 218 MG bubble
HILTON HEAD PSDAQUIFER STORAGE & RECOVERY WELL
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ADDITIONAL INFRASTRUCTURE NEEDED
16-inch transmission main into Hilton Head Plantation
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Larger mains needed to distribute new sources of water throughout island
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ADDITIONAL INFRASTRUCTURE NEEDED
• Booster station at Wild Horse Tower
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THE FUTURE
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FUTURE WATER SUPPLY OPTIONSHILTON HEAD PSD
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• Efficiency
• Expanded reused water
• Brackish Reverse Osmosiso Middle Floridano Lower Floridano Cretaceous
• Wholesale surface water
• Aquifer Storage & Recovery
PSD rain garden demonstration at Coastal Discovery Museum
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FUTURE WATER SUPPLY OPTIONSBROAD CREEK PSD
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• Additional wholesale surface water capacity
• Use of Aquifer Storage & Recovery
• Additional upgrades of pipeline infrastructure
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FUTURE WATER SUPPLY OPTIONSSOUTH ISLAND PSD
• Aquifer Storage & Recovery
• Reverse Osmosis treatment
• Distribution system upgrades
Infrastructure Planning for 20 – 25 Years Out
Sea Pines Montessori School rain garden demonstration project34
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FUTURE WATER SUPPLY OPTIONSSOUTH ISLAND PSD
• 5-year projection:o 2 ASR Wells
• Long-term projection:o Total of 5 ASR wellso 1 Reverse Osmosis plant
Short and Long Term Projections
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Questions?
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