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 Floridas Aquifers September 21-22, 2015 Fresh GW in upper FAS extent not totally known goes over 50 miles offshore on northeast coast. 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 Nations groundwater under variable climatic and anthropogenic stress. The GWRP is one of eight Water Resources Investigations Programs funded by Congress to identify, measure, and assess the Nations water resources. Principal USGS Program for addressing issues related to GW Resources, especially at the regional scale. Projects funded by GWRP fill gap between national and local scale efforts by conducting regionally integrated GW assessments In order to accomplish Program goals, the GWRP works with other Federal and non-Federal agencies and organizations. As a example, the GWRP seeks to enhance the work being conducted by the National Cooperative Water Program through collaborations with localized studies to provide a more complete picture of the Nations groundwater resources. 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 --The objectives of the regional studies are 3 fold: --These objectives will enable us to address questions that I raised earlier in the presentation. How much water do we have? How much do we need? Where are the remaining available reserves? --Moreover, this assessment is structured to provide a national perspective on the Nations ground-water resources, while simultaneously emphasizing the value of the regional assessment to those who manage and use the resources regionally and locally. 3 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 --These regional studies will have the following outcomes: --Read slideThey will produce 4 Position Relative to other Principal Aquifers
Below surficial and intermediateaquifer systems Above Southeastern Coastal Plainaquifer system Ranges in thickness from 0 ft atupdip extent to greater than 3,000ft in south Florida FAS (USGS Hydrologic Investigation Atlas 730-G) 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) From Table 9 Middle Avon Park Composite Unit typical range in Kh 0.01 to 10 ft/day, average 4 ft/day from 55 packer tests Lisbon-Avon Park no table, but has wide range also. FAS behaves as one aquifer for much of extent Regional Hydrogeologic Framework Update Completed http://pubs. usgs
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 Did major data compilation from multiple agencies in 2010 --Last data was added in May 2013 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 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 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 Middle confining units MCUI, MCUII, MCUIII, MCUV and MCUVI have been retained or reassigned. Further, because MCUI was originally mapped as a relatively thick unit containing permeable and less-permeable beds, part of this unit has been reassigned into a newly defined composite unit named the Lisbon-Avon Park composite unit, described later, and part has been reassigned to a newly defined lower permeability zone within the Upper Floridan aquifer (the OCAPLPZ, also described later). Middle confining units MCUIV and MCUVII have been abandoned. 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 Generally less-permeable lithostratigraphic units are grouped into a composite unit for subdividing the system into the Upper and Lower Floridan aquifers. A composite unit consists mostly of less-permeable rocks positioned along a narrow stratigraphic horizon defined by geologic and geophysical log markers. A composite unit also can contain areas of higher permeability rock along the same stratigraphic horizon; these higher permeability areas may have similar hydraulic properties to the aquifers bounding the composite unit above and below. The composite unit facilitates consistent mapping of the Upper and Lower Floridan aquifer across the State of Florida based on stratigraphic interval position. The numbered MCUs (IVIII) of Miller (1986) have been abandoned, remapped, or reassigned to one or both composite units or become part of a zone within the Upper or Lower Floridan aquifers, as described in the section Revised Definition and Application of the Numbered Middle Confining Units. | | | | | | | There are 2 composite units Lisbon-Avon Park composite unit and Middle Avon Park composite unit 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 Why? Facies changes result in Lisbon Avon Park grading into Avon Park permeable zone in south Florida Spatial diagram of aquifers, zones, confining and composite units
There are facies changes within stratigraphic units Entire system gets thicker to the south and the upper parts of the Avon Park become very permeable to the south All of updip Lower Floridan grades to clastic sediment from carbonates At any rate the Lisbon Avon Park composite unit grades into the aggregated Avon Park permeable zone. Springs karst features Thickness Upper Confining unit Revised mapping of many important features or other units completed and published. Thickness of Surficial aq. system Altitude 10,000 mg/L TDS-areas where lower FAS saline No changes to structural features or overall concept of flow in system. Groundwater Issues for Floridan Aquifer System
System vulnerabilities: Groundwater/surface-waterlinkage Geologic structure and salinewater encroachment External Pressures: Development & landscape change Climate change/extremes & sea- level rise Vulnerabilities makes system especially sensitive to external pressures. Finchs Cave, Marion County, FL(Photo Alan M. Cressler, USGS) Central, North, and Northwest Florida
Source: 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 Silver Springs Nitrate Source: Phelps (2004) Water-quality impacts may be attributable to not only land-use practices, but also changes in aquifer flow system affecting flow paths and geochemistry. Management of minimum flows and levels and water-quality at springs are pressing issues in FL. Lowered Lake Levels and Sinkholes
Winter Park, Florida, May (Photo Tom Scott, Florida Geological Survey) Precipitation is a huge factor in declines not just the increase withdrawals. OReilly, A.M., Roehl, E.A., Conrads, P.A., Daamen, R.C., and Petkewich, M.D., 2014, Simulation of the effects of rainfall and groundwater use on historical lake water levels, groundwater levels, and spring flows in central Florida: U.S. Geological Survey Scientific Investigations Report 20145032, 153 p. Lake Brooklyn, Clay County, Florida (Photo Mathew OMalley, St. Johns River Water Management District) (USGS Circular1278) Saline water movement through vertical fractures and horizontal permeable units (Brunswick, GA and Fernandina Beach, FL) DEPTH IN FEET Effects of saline water movement via these mechanisms tends to be localized. USGS has had good success in using seismic techniques to map collapse structures in Floridan. Mineralized water trapped by local confining units can migrate into adjacent freshwater aquifers Horizontal systems may intersect vertical systems (Williams and Spechler, 2011) Development and Landscape Change
1977 2006 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) Development and landscape change may change the partitioning of rainfall into ET, runoff, and infiltration, thus affecting short-term and long-term water levels and flows. Groundwater Withdrawal Trends, 1950-2010
In SW Georgia agricultural lands fully cultivated In some areas of coastal Georgia agriculture acreage is increases In FL mostly ag acreage stable or decreasing as urban areas spread. Large increases in Ag pumpage partly drought driven not new acreage. Total water withdrawals from the Floridan Aquifer System (modified from USGS Circular1278) Rate of Decline to Relative Degree of Confinement
Average rate of decline is 3 times greater in the confined areas vs. unconfined areas Long-term water-level decline beneath the confined areas are attributed to: Less downward leakage rate through the upper confining unit where it is thick and impermeable Increases in annual pumpage in the area Long pronounced drought coupled with pumping Higher specific yield (storage in unconfined) (Williams et al. 2011, GA Water Resources Conf.) 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 component of major pre-devel. outflows: 2% of ET 6% of Runoff Pre-development Pumpage may be relatively small component, but if this is enough to change the frequency that the system is filled and reset then it could have a significant impact on long term water levels and flows. (USGS Professional Paper 1403-C) 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 28 Major Remaining Products
Completed hydrologicconditions report- pre-development- current conditions Numerical GW model- start simple (RASA used8-mi grid cells)- add complexity aswarranted (5000-ft cell) Assessment of climatechange, sea-level rise, andmonitoring networks Thanks for the Opportunity ~ Questions ~
American Ground Water Trust Managing the Floridas Aquifers September 21-22, 2015 Orlando, Florida