Open-File Report 2011–1299
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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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.
Description of Transient Electromagnetic Soundings
Anthropogenic Factors Affecting Soundings
Data Quality and Averaging Procedure
Inversion of Transient Electromagnetic Soundings
Interpretation of Results
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