The Floridan Aquifer/Chipola River System Study

1. The Floridan Aquifer/Chipola River System Study Funded by: U.S. Geological Survey National Water Quality Assessment Program (NAWQA) and Florida Department of Environmental Protection (FDEP) Christy Crandall U.S. Geological Survey Tallahassee, Florida 850 942-9500 ext. 3030 crandall@usgs.gov

2. STUDY OBJECTIVES • Identify significant sources of nutrients to the Floridan aquifer system in the lower ACF basin and in the Chipola River basin. • Characterize hydrologic and transport processes occurring along flowpaths from areas contributing recharge to discharge points of interest using a ground-water flow and particle tracking model. • Use flow and tracking model to match nitrate concentrations in ground water from areas contributing recharge to 6 NAWQA trend wells, Jackson Blue Spring, Baltzell spring group, and Sandbag Spring—springs that flow into the Chipola River. • Use the ground-water flow and tracking model to test hypothetical scenarios changing management practices in using the flow and tracking model.

3. Contaminant occurrence in the Upper Floridan aquifer and recharging Rivers Purpose of study is to determine: Factors affecting nitrate occurrence and distribution in the Upper Floridan aquifer in the Dougherty Karst Plain • Distribution of travel times from recharge to discharge • Land use effects on nitrate concentrations • Transport processes in ground water • Effects of Withdrawals on flowpaths and travel times

4. Background and Study Area

5. Vertically contiguous sequence of limestone and dolostone of late Paleocene to early Miocene age ranging from 0 to 1250 feet thick in the study area Sand overlying clay and limestone Clay lenses in places between the sand and Limestone Highly potable Contains numerous springs, sinks and other karst features—highly vulnerable. Floridan Aquifer System

6. Extent of Floridan Topography of the Dougherty Karst Plain

7. Floridan Aquifer System in the Dougherty Karst Plain • High rates of direct recharge through sinkholes and indirect recharge through overburden—mostly sand and silty sand • High rates of discharge to large incised streams through springs.

9. Flow system Conceptualization

10. Northern Extent of Floridan Aquifer System • Confinement--Recharge occurs mainly in unconfined and semi-confined areas • Potentiometric surface—flows southward to rivers from northern extent

11. Ground water makes up the majority of discharge during low-flow conditions in the Dougherty Karst Plain. • For example at least 63 springs identified and sampled along the Chipola River. • (Barrios and Chellette, 2004)

12. Existing Models 2006 Models from Elliott Jones and Lynn Torak 1996 and 2006 • MODFE Finite element transient 2-D model developed to simulate the effects of 4000 irrigation wells on baseflowconditiotns in the Flint river.

13. Current MODFLOW Active Model-Grid Boundary Tallahassee Jones and Torak MODFE Model Boundaries

14. Comparison of Model Features MODFE Developed to simulate the effects of irrigation on the Flint/Apalachicola Rivers baseflow MODFLOWDeveloped to simulate nitrate tracking and concentrations recharging rivers Steady State Uniform cell-size (1000 m) 2 layer surficial/residuum, UFA fully 3-D model Over 4000 Wells simulated • Steady State (Torak and others, 1996) and then 1-year transient (1999-2000) (Jones and Torak, 2006) • Variable Element Size • 1 layer 2-D model • 4000 Wells simulated

15. MODLFOW model derived the following starting parameters where available from Torak and Jones • Hydraulic parameters • Aquifer tops and bottoms • Pumping data • Recharge • Boundary conditions • River and drain stage and conductance • Starting heads

16. Boundary Conditions in the MODFLOW Model

17. Simulated Withdrawals in the Upper Floridan aquifer

18. Model Calibration Data • 329 head observations in the Floridan aquifer • 65 flow observations including perennial and non-perennial streams

19. MODFLOW Budget Components  Flow in CFS • CONSTANT HEAD 3,397 • WELLS = 0.00 • NONPERENNIALS = 0.00 • PERENNIALS = 253 • HEAD DEP 5332 • RECHARGE = 1,909       • TOTAL IN 10,890       • CONSTANTHEAD2,772 • WELLS=810 • NONPERENNIALS=188 • PERENNIALS = 3124 • HEADDEP3,996 • RECHARGE=0.00 • TOTALOUT10,890

20. Simulated UFA Heads

21. Observed v. Simulated Head

22. Simulated v. Observed flows

23. Additional Modeling to define Areas Contributing Recharge

24. Regional Model • UFA broken into 3 layers • Local Grid Refinement in areas of interest • Karst Features added throughout— • Sinkhole • Conduit layer

27. Local Grid Refinement

28. Local Grid Refinement • 12 layers— • 3 in the surficial • 9 in the Floridan Improves flow path accuracy and travel time estimates Better areas contributing recharge definition

29. Flow Paths

30. Areas Contributing Recharge and Age of Water

31. Summary • Add local grids at Balztell and Sandbag Spring Group as well • Finalize nitrate travel time estimates and area contributing recharge with these models • Finish report