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REVISED HYDROGEOLOGIC FRAMEWORK OF THE FLORIDAN
AQUIFER SYSTEM
Eve Kuniansky and Jason Bellino U.S. Geological
Survey American Ground Water Trust Managing
Floridas Aquifers September 21-22, 2015
  
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USGS GROUNDWATER RESOURCES PROGRAMMISSION

• Provide objective scientific information and
  interdisciplinary understanding of aquifer
  systems
• Quantify the available groundwater and
• Assess the sustainability of the Nations
  groundwater under variable climatic and
  anthropogenic stress.

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GWRP Regional GW Availability Studies

• Objectives
• Quantify current groundwater resources
• Evaluate how these resources have changed over
  time
• Provide forecast response tools for
• climate change/weather extreme
• sea-level rise
• projected GW pumpage

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GWRP Outcomes/Products

• Trends in GW use, storage, recharge, and
  discharge
• Groundwater model that provides
• GW Budgets
• Regional context for more local studies
• Tools to make future projections
• Region-wide estimates of key variables
• Impact of future climate variability, sea-level
  rise, and projected GW use on
• GW depletion
• GW divide migration
• Sea-water intrusion
• Evaluation of adequacy of existing and potential
  future data networks

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Position Relative to other Principal Aquifers

• Below surficial and intermediate aquifer systems
• Above Southeastern Coastal Plain aquifer system
• Ranges in thickness from 0 ft at updip extent to
  greater than 3,000 ft in south Florida

FAS
(USGS Hydrologic Investigation Atlas 730-G)
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FAS is a Carbonate Rock-Karst Aquifer

• Large primary porosity in PZ
• Extremely transmissive along dissolution
  features
• At bedding planes,
• Fractures, and
• Scattered solution openings (burrowed members)

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FAS behaves as one aquifer for much of extent
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Regional Hydrogeologic Framework Update
Completedhttp//pubs.usgs.gov/pp/1807/

• Incorporated data collected since 1980s
• Abandoned numbered discontinuous middle confining
  units of Miller (1980)
• Used litho-stratigraphic mappable intervals to
  consistently divide system into Upper and Lower
  Floridan aquifers
• Incorporated sub-regional litho-stratigraphic
  zones of extremely high and less permeability
  units within the Upper and Lower Floridan aquifer

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Miller 1986 Framework

• Mapped 7 numbered discontinuous confining or
  semi-confining units in middle of FAS, 1 in LFA
• Used available hydraulic test data and
  geophysical logs, lithologic description,
  depositional history to infer hydraulic
  properties
• If no confining units present the lumped system
  called Upper Floridan aquifer
• Least permeable numbered MCU used to divide
  aquifer into Upper and Lower Floridan

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Issues with older framework

• Thousands more aquifer tests, packer tests,
  seismic datasets, and flowmeter logs available
• Most of Millers MCUs are not confining units
• very leaky and permeable
• More permeability variations mapped within
  aquifer by WMDs stratigraphic name used
• Different stratigraphic units moved into Upper or
  Lower Floridan inconsistently owing to local
  variation in hydraulic properties

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Revised Framework

• Develop more objective method to subdivide into
  Upper and Lower Floridan aquifer
• Use mappable lithological or geophysical markers
• Incorporate work of sub-regional mapping
• More permeability variations as zones within the
  Upper and Lower Floridan aquifer
• Abandon numbers for zones or units and use
  accepted stratigraphic name(s) when possible

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Provide details on geophysical log markers for
delineation of units and zones
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What is a composite unit?

• Mappable litho-stratigraphic unit(s) within the
  middle of FAS
• Generally less permeable
• Can have areas of same relative permeability as
  Upper or Lower Floridan aquifer
• Used to consistently sub-divide system into Upper
  and Lower Floridan aquifer
• Used to sub-divide system even when no confining
  unit present-hydraulic properties assigned by
  regions

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1 2 3
4 5 6 7
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Units underlying the Upper Floridan aquifer
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Units used to subdivide into Upper and Lower
Floridan
From top to bottom Bucatunna Clay confining
unit Lisbon-Avon Park composite unit north
of black line Middle Avon Park composite
unit south of black line
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Spatial diagram of aquifers, zones, confining and
composite units
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Revised mapping of many important features or
other units completed and published.
Springs karst features
Thickness Upper Confining unit
Altitude 10,000 mg/L TDS-areas where lower FAS
saline
Thickness of Surficial aq. system
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Groundwater Issues for Floridan Aquifer System

• System vulnerabilities
• Groundwater/surface-water linkage
• Geologic structure and saline water encroachment
• External Pressures
• Development landscape change
• Climate change/extremes sea-level rise

Finchs Cave, Marion County, FL (Photo Alan M.
Cressler, USGS)
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Central, North, and Northwest Florida
Source http//www.sjrwmd.com/springs/silver.html

• Reduction in spring discharge
• Increases in nitrates and other contaminants at
  some springs
• Sinkhole collapse and lakes draining during
  droughts
• Sinkhole collapse after floods
• Increased downward leakage to FAS
• Wetland reductions
• Lower lake levels

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Lowered Lake Levels and Sinkholes
Winter Park, Florida, May 1981 (Photo Tom Scott,
Florida Geological Survey)
Lake Brooklyn, Clay County, Florida(Photo Mathew
OMalley, St. Johns River Water Management
District)
(USGS Circular1278)
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Saline water movement through vertical fractures
and horizontal permeable units(Brunswick, GA and
Fernandina Beach, FL)
DEPTH IN FEET

• Mineralized water trapped by local confining
  units can migrate into adjacent freshwater
  aquifers
• Horizontal systems may intersect vertical systems

(Williams and Spechler, 2011)
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Development and Landscape Change
2006
1977

• Growing urban areas have experienced substantial
  development pressures
• For example, central Florida, 19772006? 160 ?
  in developed area? 40 ? in cropland/pasture?
  140 ? in population (1980 2010)

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Groundwater Withdrawal Trends, 1950-2010

• Total water withdrawals from the Floridan Aquifer
  System

(modified from USGS Circular1278)
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Rate of Decline to Relative Degree of Confinement
Rate of decline
Degree of confinement

• Average rate of decline is 3 times greater in the
  confined areas vs. unconfined areas

(Williams et al. 2011,GA Water Resources Conf.)
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Climate Change and Sea-Level Rise

• The FAS is stressed by the combination of
  meteorological variability and GW pumpage.
• Pumpage is relatively small component of
  hydrologic water budget.
• Meteorologically driven FAS is sensitive to
  future climate change/extremes.
• Climate change, sea-level rise, and future
  withdrawals will likely exacerbate GW depletion,
  increase sea-water intrusion , and migrate GW
  divides.

• Post-development (2000)
• Pumpage 4 BGD (0.9 in/yr)
• Represents modest componentof major pre-devel.
  outflows
• 2 of ET
• 6 of Runoff

Pre-development
(USGS Professional Paper 1403-C)
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Published Products for Floridan Study

• Digitized surfaces and hydrogeologic data from
  USGS Regional Aquifer-System Analysis (RASA)
  study of Floridan aquifer system
• Upper Floridan aquifer potentiometric map
• Upper Floridan aquifer transmissivity map
• Geophysical log database
• Revised hydrogeologic framework
• Digital Surfaces from framework

http//fl.water.usgs.gov/floridan/
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Major Remaining Products

• Completed hydrologic conditions report-
  pre-development- current conditions
• Numerical GW model- start simple (RASA used 8-mi
  grid cells)- add complexity as warranted
  (5000-ft cell)
• Assessment of climate change, sea-level rise, and
  monitoring networks

http//fl.water.usgs.gov/floridan/
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Thanks for the Opportunity Questions

• American Ground Water Trust
• Managing the Floridas Aquifers
• September 21-22, 2015
• Orlando, Florida
• http//fl.water.usgs.gov/floridan/