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Open-File Report 2011–1299

Results of Time-Domain Electromagnetic Soundings in Miami-Dade and Southern Broward Counties, Florida

By David V. Fitterman and Scott T. Prinos

Thumbnail of and link to report PDFAbstract

Time-domain electromagnetic (TEM) soundings were made in Miami-Dade and southern Broward Counties to aid in mapping the landward extent of saltwater in the Biscayne aquifer. A total of 79 soundings were collected in settings ranging from urban to undeveloped land, with some of the former posing problems of land access and interference from anthropogenic features. TEM soundings combined with monitoring-well data were used to determine if the saltwater front had moved since the last time it was mapped, to provide additional spatial coverage where existing monitoring wells were insufficient, and to help interpret a previously collected helicopter electromagnetic (HEM) survey flown in the southernmost portion of the study area.

TEM soundings were interpreted as layered resistivity-depth models. Using information from well logs and water-quality data, the resistivity of the freshwater saturated Biscayne aquifer is expected to be above 30 ohm-meters, and the saltwater-saturated aquifer will have resistivities of less than 10 ohm-meters allowing determination of water quality from the TEM interpretations. TEM models from 29 soundings were compared to electromagnetic induction logs collected in nearby monitoring wells. In general, the agreement of these results was very good, giving confidence in the use of the TEM data for mapping saltwater encroachment.

Posted December 27, 2011

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and Geochemistry Science Center
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Suggested citation:

Fitterman, D.V., and Prinos, S.T., 2011, Results of time-domain electromagnetic soundings in Miami-Dade and southern Broward Counties, Florida: U.S. Geological Survey Open-File Report 2011–1299, 289 p.



Contents

Abstract

Introduction

Description of Transient Electromagnetic Soundings

Anthropogenic Factors Affecting Soundings

Data Quality and Averaging Procedure

Inversion of Transient Electromagnetic Soundings

Interpretation of Results

Acknowledgments

References Cited

Appendix 1 Description of TEM Data Processing

Appendix 2 Description of TEM Data Files

Appendix 3 Voltage Units and Apparent Resistivity

Appendix 4 TEM Sounding Report Files: 2008

Appendix 5 TEM Sounding Descriptions and Plots: 2008

Appendix 6 TEM Sounding Report Files: 2009

Appendix 7 TEM Sounding Descriptions and Plots: 2009


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