Groundwater Continued

Consolidated

Unconsolidated

Confined

Unconfined

Aquifers

Basic Aquifer Classification

Unconsolidated or Consolidated

Consolidated: sandstone, limestone, granite

Can be low-yield or high-yield

Granite, sandstone Limestone, sand/gravel

Unconsolidated: granular sand or gravel

Consolidated Aquifer

Unconsolidated Aquifer

Low ConductivityGeologic or Soil material

Water

Highpermeability

Unconfined Aquifer

Conductivity: the ease with which water moves through material

Confined Aquifer

An inclined, water-bearing formation located below an impermeable layer of clay, rock, or shale.

High pressure

Flow

Confined and Unconfined

High pressure

Flowaquitard

Florida’s Aquifers

1. Florida has both confined and unconfined aquifers2. Florida exists on a raised platform3. The Florida platform was dominated by carbonate deposition from the Jurassic (-200 my) to the Miocene (-25 my).4. During the Miocene, clayey sediments blanketed the platform.5. These sediments form a confining unit for Florida’s main aquifer6. The major aquifer is a consolidated, carbonate confined aquifer.7. Unconfined aquifers exist above the clay confining unit.

Florida’s Aquifers

Suwannee Current

Georgia Channel

sediments

Jurassic To

Miocene

Miocene

Recent Deposits

25 to 5 Mya

200 Mya to 25 Mya

Basics

CaCO3

Clay

Sands

Sinkholes and springs are a product of the geology of Florida

Solution cavities exist in the limestone

Water in cavities is under pressure

Sinkholes: collapse of material into cavities

Springs: water bursts through thin confining units

Springs

Springs form best when the overlying clay layer is thin.

Springs

First magnitude: 100 ft3/s

Florida: 27 of 78 nationally

Confining unit less than 100 feet thick or is absent

(64.6 million gallons per day)Thin or absent

30 – 200 ft sandy

30 – 200 ft clayey

> 200 ft thick

Hawthorne Thickness

Ginnie

Poe Spring

Little Devil

http://www.underwaterflorida.homestead.com/springs.html

Manatee

Florida’s Dominant Aquifer Systems

Florida is the largest groundwater user east of the Mississippi

Floridan Aquifer

Biscayne Aquifer

Intermediate aquifer

Unconfined

Confined

Sea Levels

Temporary reestablishment of carbonate deposition

The Floridan Aquifer

The Floridan Aquifer

100,000 square miles• southern Alabama• southeastern Georgia• southern South Carolina• all of Florida

Confined

Miocene clay deposits (Hawthorne) are the confining unit

3 billion gallons per dayof freshwater withdrawn

Agriculture – 39%Domestic use – 47%Industry – 8.5%Misc.- 5.5%

Withdrawals

A thick sequence of carbonate rocks (limestone and dolomite)

The thickest and most productive formations of the system are the Avon Park Formation and the Ocala Limestone of Eocene age (37-58 million years ago)

CaCO3 + MgCO3

Water-Bearing Units

600

1200

2400

3000

ThicknessIn feet

1800

Floridan Aquifer

Biscayne Aquifer

Intermediate aquifer

surficial

The Intermediate Aquifer System

The Intermediate Aquifer System

•Between the surficial aquifer system and the Floridan aquifer system

•Used where the underlying Floridan aquifer system is deeply buried and/or contains brackish or saltwater.

•Clay confining units are above the Floridan and below the surficial aquifer.

•Artesian, but yields less water than the Floridan

•Sand, limestone, shell beds

•298 million gallons per day

Intermediate Aquifer

confined

Sand, shell, limestone

The Intermediate Aquifer System

Polk Co.

Collier Co.

flow

Polk: 120 ft

Main source ofwater supply for Charlotte, Lee, and Sarasota counties.

Floridan Aquifer:

Intermediate Aquifer:

Comparison

Withdrawal = 3 billion gal/day

Withdrawal = 298 million gal/day

Intermediate aquifer is used where the Floridan is inadequate

Surficial aquifers: The Biscayne

Surficial aquifers

Water stored above an impermeablelayer and unconfined at the surface

low conductivity

high conductivity

water

Surficial aquifers

Soils or Geologic Materials

Biscayne Aquifer

4,000 square miles

DadeBrowardPalm Beach

highly permeable sand, limestone,sandstone, shells, marl

low-permeability sandy silt

786 million gallons/day

70 % for public supply

Biscayne Aquifer

Marls: carbonate-rich muds containing clays and calciteOolitic limestone: spheroidal carbonate grains with a mineral cortex

Plio-pliestocence

EoceneMiocene

240 ft

Thickness

Water in the Biscayne

Recharge

Flow

Recharge and Flow

Pesticides, fertilizers, landfills, septic systems, injection wells

Injection well

Salt water

pumping Salinization

Coastal Canals

Inland Canals

Flood Control

pollu

tant

s

Floridan Aquifer:

Intermediate Aquifer:

Biscayne Aquifer

Three Major Florida Aquifers

Withdrawal = 3 billion gal/day

Withdrawal = 298 million gal/day

Withdrawal = 786 million gallons/day

Total = 4.084 billion gallons/day

Floridan Aquifer

Biscayne Aquifer

Intermediate aquifer

Unconfined

ConfinedConfined