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Scientific Investigations Report 2009–5113

Prepared in cooperation with South Florida Water Management District

Hydrogeologic and Hydraulic Characterization of the Surficial Aquifer System, and Origin of High Salinity Groundwater, Palm Beach County, Florida

By Ronald S. Reese and Michael A. Wacker

COVER OF REPORT

Abstract

Previous studies of the hydrogeology of the surficial aquifer system in Palm Beach County, Florida, have focused mostly on the eastern one-half to one-third of the county in the more densely populated coastal areas. These studies have not placed the hydrogeology in a framework in which stratigraphic units in this complex aquifer system are defined and correlated between wells. Interest in the surficial aquifer system has increased because of population growth, westward expansion of urbanized areas, and increased utilization of surface-water resources in the central and western areas of the county. In 2004, the U.S. Geological Survey, in cooperation with the South Florida Water Management District, initiated an investigation to delineate the hydrogeologic framework of the surficial aquifer system in Palm Beach County, based on a lithostratigraphic framework, and to evaluate hydraulic properties and characteristics of units and permeable zones within this framework.

A lithostratigraphic framework was delineated by correlating markers between all wells with data available based primarily on borehole natural gamma-ray geophysical log signatures and secondarily, lithologic characteristics. These correlation markers approximately correspond to important lithostratigraphic unit boundaries. Using the markers as guides to their boundaries, the surficial aquifer system was divided into three main permeable zones or subaquifers, which are designated, from shallowest to deepest, zones 1, 2, and 3. Zone 1 is above the Tamiami Formation in the Anastasia and Fort Thompson Formations. Zone 2 primarily is in the upper part or Pinecrest Sand Member of the Tamiami Formation, and zone 3 is in the Ochopee Limestone Member of the Tamiami Formation or its correlative equivalent. Differences in the lithologic character exist between these three zones, and these differences commonly include differences in the nature of the pore space.

Zone 1 attains its greatest thickness (50 feet or more) and highest transmissivity in coastal areas. Zone 2, the most transmissive and extensive zone, is thickest (80 feet or more) and most transmissive in the inland eastern areas near Florida’s Turnpike. In this area, zone 1 is absent, and the semiconfining unit above zone 2 extends to the land surface with a thickness commonly ranging from 50 to 100 feet. The thickness of zone 2 decreases to zero in most wells near the coast. Zone 3 attains its greatest thickness (100 feet or more) in the southwestern and south-central areas; zone 3 is equivalent to the gray limestone aquifer.

The distribution of transmissivity was mapped by zone; however, zones 2 and 3 were commonly combined in aquifer tests. Maximum transmissivities for zone 1, zones 2 and 3, and zone 3 were 90,000, 180,000, and 70,000 ft2/d (feet-squared per day), respectively. The northern extent of the area with transmissivity greater than 50,000 ft2/d for zones 2 and 3 in the inland northeastern area along Florida’s Turnpike has not been defined based on available data and could extend 5 to 10 miles farther north than mapped. Based on the thickness of zone 2 and a limited number of aquifer tests, a large area of zone 2 with transmissivity greater than 10,000 ft2/d, and possibly as much as 30,000 ft2/d, extends to the west across Water Conservation Area 1 from the inland southeastern area into the south-central area and some of the southwestern area.

In contrast to the Biscayne aquifer present to the south of Palm Beach County, zones 2 and 3 are interpreted to be present principally in the Tamiami Formation and are commonly overlain by a thick semiconfining unit of moderate permeability. These zones have been referred to as the “Turnpike” aquifer in the inland eastern areas of Palm Beach County, and the extent of greatest thickness and transmissivity follows, or is adjacent to, Florida’s Turnpike. Where it is thick and transmissive, zone 1 may be considered equivalent to the Biscayne aquifer.

Areas of high salinity groundwater in the surficial aquifer system in the central and western areas of the county have been identified and mapped in previous studies, and water samples were collected in this study to gain a better understanding of the origin of this water. Based primarily on strontium concentration and isotope data, as well as hydrogen and oxygen isotope data, evidence for upwelling and invasion of the surficial aquifer system with brackish or saline water from the Floridan aquifer system or deeper was not found. The seawater age indicated by strontium isotope ratios measured in water produced from wells sampled in the central and western areas correlates with the expected age of the sediments open in a well, which indicates that the residual invaded or relict seawater theory for the origin of this high salinity water is most probable.

Produced October 2009

For additional information contact:
Ron Reese
rsreese@usgs.gov
U.S. Geological Survey
Florida Water Science Center
3110 SW 9th Avenue
Ft. Lauderdale, FL 33315

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Appendix 2 is presented in WellCAD™ format (WCL) and requires the WellCAD™ reader to view it. The reader is provided or download it free of charge from the WellCAD™ website.


Suggested citation:

Reese, R.S., and Wacker, M.A., 2009, Hydrogeologic and Hydraulic Characterization of the Surficial Aquifer System, and Origin of High Salinity Groundwater, Palm Beach County, Florida: U.S. Geological Survey Scientific Investigations Report 2009–5113, 83 p., (appendixes on CD).



Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Investigations

Methods of Investigation

Well Drilling and Construction and Inventory of Wells

Borehole Geophysical Logging

Description of Lithologic Samples

Aquifer Testing

Water-Quality Data Collection

Lithostratigraphic Framework Delineation

Hydrostratigraphic Framework Delineation

Hydrogeologic Framework

Lithostratigraphic Framework

Hydrostratigraphic Units

Zone 1

Zone 2

Zone 3

Hydraulic Properties and Characteristics

Hydraulic Test Data

Comparison of Transmissivity Derived by Different Methods

Confinement above Zone 2 or 3

Characteristics of Flow Zones as Determined by Borehole Geophysical Logs

Distribution of Transmissivity by Zone

Zone 1

Zone 2 or Zones 2 and 3 Combined

Zone 3

Aquifer Nomenclature and Definition

Origin of High Salinity Groundwater in Central and Western Parts of the Study Area

Summary and Conclusions

References Cited

Appendix 1

Appendix 2



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