Lester J. Williams and Rick M. Spechler 4/26/2011

1. Horizontal Bedding-Plane Conduit Systems in the Floridan AquiferSystem and Their Relation to Saltwater Intrusion in NortheasternFlorida and Southeastern Georgia Lester J. Williams and Rick M. Spechler 4/26/2011

2. Outline • Hydrogeology of the Floridan Aquifer System in Northeastern Florida and Southeastern Georgia • Acoustic televiewer images of conduit systems from various wells in area • Relation to saltwater intrusion

3. Floridan Aquifer System • Permeable carbonate rock aquifer • Several hundred to several thousand feet thick • Principal source of water in region • Underlies an area of about 100,000 square miles

4. Aquifer Confinement • Unconfined Areas • Extensive karst development • Confined Areas • Less karstic • Deeper saline highly cavernous boulder zone and Fernandina Permeable Zone Study Area Modified from Bush and Johnson, 1988

5. Aquifers and Confining Units

6. Site Location Map Showing Wells Used in Revising Framework

7. Key Well Site: Test Well 26 Colonels Island

8. Hydrogeologic Units • Upper Confining Unit • Upper Floridian Aquifer • Lower Floridan Aquifer • Fernandina Permeable Zone Freshwater Freshwater High Sulfate Saltwater

9. Middle Confining Units in the Floridan Aquifer System

10. Ware Co. GA: Waycross Test Hole

11. WaycrossTest well Focused (guard) Resistivity Gamma Ray MCU I Logs from files of the USGS Denotes a geophysical marker bed

12. Lower marker beds below MCU I marker beds (dolostone) Logs from files of the USGS

13. Nassau Co. FL: Fernandina Beach

14. Nassau County FL Focused (guard) Resistivity Long and Short Normal Gamma Ray MCU I (lower marker beds) Logs from files of the USGS

15. Correlation D D’ 56 miles Fernandina Beach, FL Waycross, GA

16. What is the relation between the hard dolostone beds (i.e. confining units) and horizontal conduit systems? • Horizontal conduit systems tend to develop on top or below the hard dolostone units • Because the hard beds are fairly persistent across study area it makes it possible to start to visualize an organization to the permeable systems • We can view these in some of the acoustic televiewer (ATV) images collected from the open portion of boreholes

17. Acoustic Televiewer Images • Collected by USGS in the late 1970’s to mid 1990’s • These were scanned in from original Polaroid images • Show a 360 degree oriented image of the inside of the open portion of the borehole Stitched together Polaroids of ATV image from test well in Brunswick, GA

18. Televiewers

19. Dip direction

20. Projected image on 2-D plane

21. Core view (wrapped) Projected view of borehole wall

22. ATV Images: Brunswick

23. TW-26 Colonels Island, Brunswick GA

24. Solution Zones in the Avon Park Formation

25. Characteristics of solution zones in Avon Park Formation • Appear to be formed preferentially along dolostone or dolomitic limestone intervals • Each solution zone consists of many individual pipes and openings • Zones of solution openings range from few feet to several 10’s of feet

26. Solution Zones in the Oldsmar Formation

27. Fractures • Very few observed in ATV images • Most are observed in the cavernous zones possibly associated with collapse? • Relative absence of fracturing in ATV images suggest that vertical fracture systems must be widely spaced or more related to collapse features described by others working in area Fracture

28. Conduit systems in relation to production zones at Colonels Island Well • Orange dots represent horizontal bedding plane opening • Red dots are scattered vuggy systems • Dark blue dots are steep fractures (not many) • Biggest flow zones correspond to major lithologic contacts Brunswick, GA

29. Conduit systems in relation to production zones at Colonels Island Well • Flowmeter surveys indicate discrete flow zones located near top or base of confining units TW-26, Brunswick, GA

30. ATV Image Locations: Waycross

31. Waycross Test Hole 870-890 900-920 920-940

32. Waycross Test Hole 1080-1100 1100-1120 1130-1150

33. ATV Image Locations: Jacksonville

34. Lovegrove Well Field, Jacksonville FL • Scattered solution lenticular shaped openings • Also discrete 2 to 6-inch wide bedding plane openings in other wells of area (not shown here) From Phelps and Spechler, 1997

35. Relation of Horizontal Conduits to Saltwater Intrusion • Long-term decreases in potentiometric surface of aquifer • Inversely related to increases in chloride

36. Pre-Development Flow System From: Krause and Randolph, 1989

37. Post-Development Flow System From: Krause and Randolph, 1989

38. What is the Effect of Horizontal Systems on Saltwater Intrusion? ? ?

39. Effects of Horizontal Systems • Mineralized water trapped in local confining units can migrate into adjacent freshwater aquifers • Horizontal systems may intersect vertical systems Freshwater Mineralized Water Freshwater High Sulfate Saltwater TW-26 Brunswick, GA

40. Conceptual Model • As water is pumped from the conduit systems leakage is induced from adjacent confining beds or from intersecting vertical fractures

41. Revised Conceptual Model of Flow

42. Sources of Salt Water • Trapped connate water inside confining beds • Saline aquifers near base of system

43. Cross Sections • Deep water test wells • Oil test wells • Some of the older oil test wells were the best for correlating across the full thickness of aquifer Southeastern Georgia Embayment Peninsular Arch

44. North-South Section

45. East-West Section

46. Summary • Highly permeable solution zones tend to develop along bedding planes and at major lithologic contacts throughout the study area • Where tapped the transmissive zones supply most of the water to wells that tap them • Mineralized water contained in adjacent lower-permeability confining units may be drawn into the horizontal systems through pumping • Saltwater intrusion may also occur from upward migrating saline water along vertical discontinuities into the horizontal systems

47. Acknowledgments • Jeff Davis, SJRWMD • Don Boniel, SJRWMD • Harold Gill, USGS Ret.