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Floating Electromagnetic Surveys from the Lower Delaware River Basin

Dates

Publication Date
Start Date
2020-08-26
End Date
2021-08-27

Citation

Rey, D.M., Briggs, M.A., Terry, N.C., White, E.A., and Trottier, B., 2022, Floating Electromagnetic Surveys from the Lower Delaware River Basin: U.S. Geological Survey data release, https://doi.org/10.5066/P9X8RUBW.

Summary

Electromagnetic (EM) geophysical methods provide information about the bulk electrical conductivity of the subsurface. EM data has been widely used to investigate aquifers and geologic structures. In the following study, the United States Geological Survey conducted a boat-towed, waterborne transient electromagnetic (FloaTEM) survey to examine conductivity within the subsurface of the main Delaware River channel and the Leipsic River. The Leipsic River flows through an estuary into the Delaware Bay. Subsurface conductive zones, when viewed in the context of the regional conceptual model and other data, can help determine the likely groundwater location of the freshwater/saltwater interface within the Delaware River, as well as key [...]

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DRB_FloaTEM_thumbnail.jpg thumbnail 189.73 KB image/jpeg
FloaTEM.zip 11.66 MB application/zip
FloaTEM_dictionary.csv 4.11 KB text/csv
readme.txt 3.3 KB text/plain
version_history.txt 2.61 KB text/plain
YSI.zip 968.68 KB application/zip
YSI_dictionary.csv 1.57 KB text/csv

Purpose

Saltwater is more electrically conductive than freshwater, making EM methods a useful tool for mapping the spatial extent of freshwater/saltwater interfaces. Little information is available about the spatial extent of the freshwater/saltwater groundwater interface near the mouth of the Delaware River. Mapping this interface, which is not directly reflected by the surface water salt front, is important to understanding and monitoring the relative salinity of aquifers below the river and areas of possible groundwater/surface water exchange. Consequently, FloaTEM surveys were conducted to help characterize this interface. However, lithology can also impact the bulk electrical conductivity measured with EM methods. Therefore, repeat data collection can be a useful means for observing changes in pore water salinity, assuming the background lithology remains constant. In areas where pore water specific conductance is expected to be relatively homogeneous, results can be directly interpreted in terms of lithology. There were four objectives for this work: [1] attempt to characterize the groundwater fresh/saline interface near the mouth of the Delaware River, [2] perform repeat data collection (2020 versus 2021) in these areas to observe if significant changes have occurred between years, [3] test the FloaTEM system in the highly urbanized Philadelphia area as a possible method for mapping hydrogeology and specifically, determining riverbed connectivity to permeable hydrogeology, and, [4] evaluate use of the FloaTEM system for exploring fresh/saltwater dynamics and hydrogeology in an estuary.
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DOI https://www.sciencebase.gov/vocab/category/item/identifier doi:10.5066/P9X8RUBW

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