Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Skip to content

Floating Electromagnetic Surveys from the Lower Delaware River Basin

Metadata Updated: July 6, 2024

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 hydrogeological layers such as the Lower Potomac-Raritan-Magothy Aquifer within the Northern Atlantic Coastal Plain Aquifer System, and their connectivity with the riverbed. Permeable aquifers could provide a hydraulic connection between surface water and inland groundwater. Therefore, changes to river water salinity could have an accelerated impact on water pumped from wells inland that are connected via these permeable aquifers. The FloaTEM system transmits a primary electrical current through a transmitter loop (Tx) wire. This creates a static primary magnetic field. Then, the current in the TX loop is subsequently turned off, resulting in secondary electrical currents being induced in the earth. These induced electrical currents decay with time, and this rate of decay in the secondary electrical field is a function of the bulk conductivity of the subsurface material. As the secondary electrical field decays, a secondary magnetic field is induced and measured at a receiver (Rx) loop towed behind the Tx loop. The Rx loop measures the decay of the secondary magnetic field as a function of time (dB/dt). Measured dB/dt decay curves can be inverted to recover the depth-dependent resistivity structure of the earth. FloaTEM surveys were conducted downstream from Wilmington, DE on 8/26/2020 and 8/27/2020. Data from 8/26/2020 were collected around the Augustine Wildlife Area boat ramp, and data on 8/27/2020 were collected near the Collins Landing boat ramp. FloaTEM surveys were again conducted downstream from Wilmington, DE on 8/25/2021 and 8/26/2021. Data from 8/25/2021 were collected upstream of the 2020 surveys around the Pennsville public boat ramp, while data on 8/26/2021 were collected near the Collins Landing boat ramp and covered a similar area as the 2020 data. Data collected in 2021 also included a section of the Delaware River further upstream near Philadelphia PA, collected on 8/24/2021 and made use of the Fort Mifflin boat ramp. A final back and forth profile in the Leipsic River within the Bombay Hook National Wildlife Refuge (estuary) was gathered on 8/27/21, and used the Port Mahon Boat Launch as the starting/ending point. Surface water specific conductance data were also collected during portions of the surveys.

Access & Use Information

Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

Downloads & Resources


Metadata Created Date June 1, 2023
Metadata Updated Date July 6, 2024

Metadata Source

Harvested from DOI EDI

Additional Metadata

Resource Type Dataset
Metadata Created Date June 1, 2023
Metadata Updated Date July 6, 2024
Publisher U.S. Geological Survey
Identifier USGS:6327d40fd34e71c6d67b70e2
Data Last Modified 20221219
Category geospatial
Public Access Level public
Bureau Code 010:12
Metadata Context
Metadata Catalog ID
Schema Version
Catalog Describedby
Harvest Object Id 9ce27508-d9b0-48b7-bd70-a50ea2137108
Harvest Source Id 52bfcc16-6e15-478f-809a-b1bc76f1aeda
Harvest Source Title DOI EDI
Metadata Type geospatial
Old Spatial -75.6038,39.1556,-75.1437,39.5062
Publisher Hierarchy White House > U.S. Department of the Interior > U.S. Geological Survey
Source Datajson Identifier True
Source Hash 473e9316845e51512fda1d3059593322e5dfb7ee8223a9d40238fbe51d1b6121
Source Schema Version 1.1
Spatial {"type": "Polygon", "coordinates": -75.6038, 39.1556, -75.6038, 39.5062, -75.1437, 39.5062, -75.1437, 39.1556, -75.6038, 39.1556}

Didn't find what you're looking for? Suggest a dataset here.