U.S. Department of the Interior
U.S. Geological Survey
FS-158-96



Project Goal |
Background |
Geologic Framework of the Aquifer System |
Geophysical Investigations |
Research Plan |
Collaboration and Partnerships

Restoration and management of the south Florida ecosystem will be guided
 by hydrologic models that simulate water flowing through the wetlands 
and shallow subsurface aquifers beneath them. The restoration of the
 ecosystem is, essentially, the restoration of the natural hydrologic 
system.  As surface water is re-diverted from manmade canals to its more 
natural state as overland flow, several changes are predicted to occur. 
 First, because water flowing over land moves more slowly than in 
canals, overland flow should remain in the wetland ecosystem for a 
longer period each year.  Second, as the flowing water spreads out
 over the wetlands, recharge to the shallow aquifers should increase 
as more of that water infiltrates into the ground.  The U.S. Corps of 
Engineers and the South Florida Water Management District (SFWMD) will 
use hydrologic models to anticipate the consequences of these proposed 
restoration plans.  
This research program is designed to provide essential subsurface 
data to improve hydrologic models for land and water managers in 
southwest Florida where subsurface information is lacking.  
Obtaining hydrogeological data requires core drilling, corehole 
testing, and rock and sediment analysis. 
Project Goal

The objective of this project is to provide to hydrologic modelers a 
three-dimensional database of the geologic and hydrologic properties of 
the sediments and rocks of the surficial aquifer system in southwest 
Florida, in Collier and Monroe Counties.  Emphasis will be placed on 
the geologic framework of the aquifer.

Background

|map showing location of project study area
|------------------------------------------
|Figure 1. Project study area.             

Nearly all sediment and rock in the subsurface of south Florida contains
 ground water;  however, much of that water is not accessible for use. 
 Zones from which economically significant quantities of water can be 
withdrawn are called aquifers.  The most important properties of an aquifer
 are porosity and permeability.  Porosity is the amount of void space 
(pores) in sediment or rock that water can occupy, and permeability is 
the rate at which water can flow between those pores.  The quantity and 
flow rate of ground water in aquifers are determined primarily by 
differences in porosity and permeability.  These important sediment 
and rock properties were determined in the geologic past by a 
combination of original depositional processes, by past and present
 dissolution of the rock, and by the precipitation of new minerals.  
In other words, the rocks of an aquifer system have a history, and 
understanding that history will enable us to construct more realistic
 hydrologic models and to approximate aquifer properties between 
sampling sites.  In southwest Florida, the surficial aquifer system 
(from the water table down to a depth of about 200 feet) is the primary
 source of freshwater.  This system includes the water-table aquifer, 
the lower Tamiami aquifer, and the confining unit (rock and sediment of
 low permeability) that separates them. Surface water that flows through 
the wetlands is in the water-table aquifer.

Geologic Framework of the Aquifer System

|photo of sampling equipment
|---------------------------

Geophysical InvestigationsGeophysical logs provide a continuous downhole record of the properties 
of the rocks that form the aquifer. They are especially valuable in 
providing physical and chemical properties of the corehole where 
particular intervals of core recovery are poor.  Also, they allow 
extension of hydrologic test data from discrete samples to the 
rest of the core.
Geophysical logs, combined with aquifer water properties and flow 
measurements, will be used to relate large-scale ground-water 
circulation to the distribution of hydrologic properties of the 
aquifer.  For example, flowmeter logs can confirm that the most 
permeable intervals, as inferred from core measurements, coincide 
with the intervals that conduct the most flow in the vicinity of 
test wells.  Geophysical logs also will indicate which confining 
units act to separate the aquifer system into discrete aquifers having 
different water quality and hydraulic head.Research PlanApproximately 40 coreholes will be drilled through the surficial 
aquifer system, averaging 200 feet in depth.Geophysical logs will be run after the holes are drilled. Geophysical
 probes will be placed into the coreholes to determine water and rock
composition, rock porosity, water-flow rates, hole diameter, and roughness. 
 A flowmeter will be used to measure direction (up or down) and magnitude
 of flow in the aquifer at specific depths.Cores will be examined for mineralogy, texture, sedimentary structures, 
and fossils to determine rock type, age, mineralization, and porosity and 
to differentiate the zones that form aquifers from the confining units
 that separate them.Stratigraphic units will be identified and correlated between 
coreholes and their properties estimated where core data are absent.Permeability will be measured on core samples, and the data 
integrated with hydrologic and geophysical logs, to estimate the rate
 at which ground water moves through the aquifer.Aquifer tests will be performed on selected coreholes to measure permeability of the aquifer system.Product Plans:- yearly reports of geophysical, stratigraphic, and hydrologic data
  - report summarizing the geologic history of the surficial aquifer system in
    southwest Florida
  - regional geologic cross sections of the
    surficial aquifer system of southwest
    FloridaCollaboration and PartnershipsU.S. Geological Survey (USGS) scientists in this project have formed
a partnership with the Florida Geological Survey (FGS).  The FGS and 
USGS will share responsibility for drilling the coreholes, describing
 the core, and performing permeability testing.  The FGS will curate 
the cores and make them available to all scientists at their warehouse
 facility in Tallahassee after analyses are completed. The FGS maintains 
an electronic lithologic data base on the World Wide Web and will 
include descriptions of all cores drilled in that data base. Mapping 
the spatial distribution of hydraulic conductivity in the aquifer
 system will require the integration of all data collected by both agencies.
   Members of this project are coordinating with another USGS/SFWMD 
cooperative study, in an area where the two studies overlap, to assess
 the gray limestone aquifer of the surficial aquifer system of central 
and southeast Florida as a source of public-supply water.  The two 
projects will share the same corehole sites in the Big Cypress 
National Preserve.Anticipated Schedule:February 1996: Begin corehole drilling in Collier County.June 1996: Begin sample analyses and aquifer testing.October 1996: Compile report of previous year\071s drilling.January 1997: Begin drilling in Big Cypress National Preserve; continue
     sample analyses.October 1997: Compile report of Big Cypress study; continue sample
     analyses.January 1998: Begin drilling in northern Collier County; continue sample
     analyses, and aquifer testing.October 1998: Compile report of previous year\071s drilling; continue sample
     analyses.January 1999: Finish drilling and begin synthesis reports and cross 
sections.


For more information contact:Suzanne D. Weedman
			U.S. Geological Survey, MS 926A
			Reston, VA  20192
			(703) 648-6379sweedman@usgs.gov

Related information:SOFIA Project: Hydrogeology of the Surficial Aquifer System in Southwest Florida







		

		| Disclaimer | Privacy Statement | Accessibility |
					U.S. Department of the Interior, U.S. Geological Survey
							This page is: http://sofia.usgs.gov/publications/fs/158-96/print.html
							Comments and suggestions? Contact: Heather Henkel - Webmaster
							Last updated: 05 November, 2004 @ 10:31 AM(TJE)