REVISED HYDROGEOLOGIC FRAMEWORK OF THE FLORIDAN AQUIFER SYSTEM

REVISED HYDROGEOLOGIC FRAMEWORK OF THE FLORIDAN AQUIFER SYSTEM Eve Kuniansky and Jason Bellino U. S. Geological Survey American Ground Water Trust Managing Florida’s Aquifers September 21 -22, 2015

USGS GROUNDWATER RESOURCES PROGRAM MISSION Provide objective scientific information and interdisciplinary understanding of aquifer systems Quantify the available groundwater and Assess the sustainability of the Nation’s groundwater under variable climatic and anthropogenic stress.

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

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

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 (USGS Hydrologic Investigation Atlas FAS

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)

FAS behaves as one aquifer for much of extent

Regional Hydrogeologic Framework Update Completed http: //pubs. usgs. gov/pp/1807/ • Incorporated data collected since 1980’s • 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

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

Issues with older framework • Thousands more aquifer tests, packer tests, seismic datasets, and flowmeter logs available – Most of Miller’s MCU’s are not confining units • very leaky and permeable – More permeability variations mapped within aquifer by WMD’s– stratigraphic name used – Different stratigraphic units moved into Upper or Lower Floridan inconsistently owing to local variation in hydraulic properties

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

Provide details on geophysical log markers for delineation of units and zones

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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Units underlying the Upper Floridan aquifer

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

Spatial diagram of aquifers, zones, confining and composite units

Springs karst features Thickness of Surficial aq. system Thickness Upper Confining unit Revised mapping of many important features or other units completed and published. Altitude 10, 000 mg/L TDS-areas where lower FAS saline

Groundwater Issues for Floridan Aquifer System vulnerabilities: • Groundwater/surface-water linkage • Geologic structure and saline water encroachment External Pressures: • Development & landscape change • Climate change/extremes & sealevel rise Finch’s Cave, Marion County, FL (Photo Alan M. Cressler, USGS)

• Central, North, and Northwest Reduction in spring discharge Florida – 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 Source: http: //www. sjrwmd. com/springs/silver. html Silver Springs Nitrate Source: Phelps (2004)

Lowered Lake Levels and Sinkholes Winter Park, Florida, May 1981 Lake Brooklyn, Clay County, Florida (Photo Tom Scott, Florida Geological Survey) (Photo Mathew O’Malley, St. Johns River Water Management District) (USGS Circular 1278)

Saline water movement through vertical fractures and horizontal permeable units DEPTH IN FEET (Brunswick, GA and Fernandina Beach, FL) • Mineralized water trapped by local confining units can migrate into adjacent freshwater aquifers (Williams and Spechler, 2011) • Horizontal systems may intersect vertical

Development and Landscape Change • Growing urban areas have experienced substantial development pressures • For example, central Florida, 1977– 2006: ▪ 160% ↑ in developed area ▪ 40% ↓ in cropland/pasture ▪ 140% ↑ in population (1980 – 2010) 1977 2006

Groundwater Withdrawal Trends, 1950 -2010 Total water withdrawals from the Floridan Aquifer System (modified from USGS Circular 1278)

Rate of Decline to Relative Degree of Confinement Rate of Degree of decline • Average rate of decline is 3 times greater in the confined areas vs. unconfined areas (Williams et al. 2011, GA Water Resources Conf. ) confinement

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 , Post-development (2000) Preand migrate GW divides. development (USGS Professional Paper 1403 -C) Ø Pumpage 4 BGD (0. 9 in/yr) Represents modest componen of major pre-devel. outflows: Ø 2% of ET Ø 6% of Runoff

• 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/

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/

Thanks for the Opportunity ~ Questions ~ American Ground Water Trust Managing the Florida’s Aquifers September 21 -22, 2015 Orlando, Florida http: //fl. water. usgs. gov/floridan/