USGS OFR 2008-1364 --- Reich and others

Investigation of Coastal Hydrogeology Utilizing Geophysical and Geochemical Tools along the Broward County Coast, Florida

Christopher D. Reich, Peter W. Swarzenski, W. Jason Greenwood, and Dana S. Wiese

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CONTENTS
Abstract
Introduction
      Statement of Problem
      Purpose and Scope
      Approach
Description of Study Area
      Population
      Geologic Setting
      Hydrogeology
      Precipitation
Methods of Investigation
      Radon
      Continuous Resistivity Profiles
      Seismic
Results and Discussion
      Geochemical Data
            Time-Series Radon
            Radium
      Geophysical Data
            Continuous Resistivity Profiling
            High-Resolution Seismic Profiling
Summary and Conclusions
Acknowledgments
References Cited
Appendix A
Appendix B
Appendix C

Abstract

Geophysical (CHIRP, boomer, and continuous direct-current resistivity) and geochemical tracer studies (continuous and time-series ²²²Radon) were conducted along the Broward County coast from Port Everglades to Hillsboro Inlet, Florida. Simultaneous seismic, direct-current resistivity, and radon surveys in the coastal waters provided information to characterize the geologic framework and identify potential groundwater-discharge sites. Time-series radon at the Nova Southeastern University National Coral Reef Institute (NSU/NCRI) seawall indicated a very strong tidally modulated discharge of ground water with ²²²Rn activities ranging from 4 to 10 disintegrations per minute per liter depending on tidal stage. CHIRP seismic data provided very detailed bottom profiles (i.e., bathymetry); however, acoustic penetration was poor and resulted in no observed subsurface geologic structure. Boomer data, on the other hand, showed features that are indicative of karst, antecedent topography (buried reefs), and sand-filled troughs. Continuous resistivity profiling (CRP) data showed slight variability in the subsurface along the coast. Subtle changes in subsurface resistivity between nearshore (higher values) and offshore (lower values) profiles may indicate either a freshening of subsurface water nearshore or a change in sediment porosity or lithology. Further lithologic and hydrologic controls from sediment or rock cores or well data are needed to constrain the variability in CRP data.

Suggested Citation:

Reich, C.D., Swarzenski, P.W., Greenwood, J.W., and Wiese, D.S., 2009, Investigation of coastal hydrogeology utilizing geophysical and geochemical tools along the Broward County coast, Florida: U.S. Geological Survey Open-File Report 2008-1364, 21 p., plus apps. A-C.

For more information, contact:

U.S. Geological Survey
Florida Integrated Science Center
U.S. Geological Survey
600 4th Street South
St. Petersburg, FL 33701

Christopher D. Reich at creich@usgs.gov

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