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Horizontal Bedding-Plane Conduit Systems in the Floridan Aquifer System and Their Relation to Saltwater Intrusion in Northeastern Florida and Southeastern Georgia. Lester J. Williams and Rick M. Spechler 4/26/2011. Outline.

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lester j williams and rick m spechler 4 26 2011

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

outline
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
floridan aquifer system
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
aquifer confinement
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

hydrogeologic units
Hydrogeologic Units
  • Upper Confining Unit
  • Upper Floridian Aquifer
  • Lower Floridan Aquifer
  • Fernandina Permeable Zone

Freshwater

Freshwater High Sulfate

Saltwater

waycrosstest well
WaycrossTest well

Focused (guard)

Resistivity

Gamma Ray

MCU I

Logs from files of the USGS

Denotes a geophysical marker bed

lower marker beds below mcu i
Lower marker beds below MCU I

marker

beds

(dolostone)

Logs from files of the USGS

nassau county fl
Nassau County FL

Focused (guard)

Resistivity

Long and Short

Normal

Gamma Ray

MCU I

(lower marker beds)

Logs from files of the USGS

correlation
Correlation

D

D’

56 miles

Fernandina Beach, FL

Waycross, GA

slide16
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
acoustic televiewer images
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

slide21

Core

view

(wrapped)

Projected view

of borehole wall

characteristics of solution zones in avon park formation
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
fractures
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

conduit systems in relation to production zones at colonels island well
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

conduit systems in relation to production zones at colonels island well29
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

waycross test hole
Waycross Test Hole

870-890

900-920

920-940

waycross test hole32
Waycross Test Hole

1080-1100

1100-1120

1130-1150

lovegrove well field jacksonville fl
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

relation of horizontal conduits to saltwater intrusion
Relation of Horizontal Conduits to Saltwater Intrusion
  • Long-term decreases in potentiometric surface of aquifer
  • Inversely related to increases in chloride
pre development flow system
Pre-Development Flow System

From: Krause and Randolph, 1989

post development flow system
Post-Development Flow System

From: Krause and Randolph, 1989

effects of horizontal systems
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

conceptual model
Conceptual Model
  • As water is pumped from the conduit systems leakage is induced from adjacent confining beds or from intersecting vertical fractures
sources of salt water
Sources of Salt Water
  • Trapped connate water inside confining beds
  • Saline aquifers near base of system
cross sections
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

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