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 Delaware River channel. These conductive zones determine the location of the groundwater freshwater/saltwater interface within the Delaware River, downstream from Wilmington, DE. 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 on 2/26/2020 were collected around the Augustine Wildlife Area boat ramp, and data on 8/27/2020 were collected near the Collins Landing boat ramp.

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.

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.

Floating transient electromagnetic (FloaTEM) data were acquired on the Upper Delaware River during December 2018. During the survey, approximately 10 line-kilometers were collected in the Upper Delaware River, near USGS boring 12008-14 (https://webapps.usgs.gov/GeoLogLocator/#!/search) near Barryville, New York study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, New England Water Science Center, and the National Park Service UPDE. FloaTEM data acquired along the Delaware River in Sullivan County, in New York, were collected to test a new continuous water-borne transient electromagnetic data collection platform, and to characterize the subsurface resistivity structure. FloaTEM data were collected using an Aarhus University HydroGeophysics Group FloaTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted FloaTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed.Data locations are provided as UTM Zone 18 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-imapcted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 18 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 18 N projection and datum of WGS-84. (4) Files with *WATER-DEPTH_DATA.xyz and *WATER-DEPTH_DATA.csv are space- and comma-delimited ASCII files containing the water-depth data as measured from the bottom of the transducer. Water-depth measurement locations are provided as UTM Zone 18 N, WGS-84. (5) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

Floating transient electromagnetic (FloaTEM) data were acquired on the Upper Delaware River during December 2018. During the survey, approximately 10 line-kilometers were collected in the Upper Delaware River, near USGS boring 12008-14 (https://webapps.usgs.gov/GeoLogLocator/#!/search) near Barryville, New York study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, New England Water Science Center, and the National Park Service UPDE. FloaTEM data acquired along the Delaware River in Sullivan County, in New York, were collected to test a new continuous water-borne transient electromagnetic data collection platform, and to characterize the subsurface resistivity structure. FloaTEM data were collected using an Aarhus University HydroGeophysics Group FloaTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted FloaTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed.Data locations are provided as UTM Zone 18 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-imapcted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 18 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 18 N projection and datum of WGS-84. (4) Files with *WATER-DEPTH_DATA.xyz and *WATER-DEPTH_DATA.csv are space- and comma-delimited ASCII files containing the water-depth data as measured from the bottom of the transducer. Water-depth measurement locations are provided as UTM Zone 18 N, WGS-84. (5) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

Surface and water-borne geophysical methods can provide information for the characterization of the subsurface structure of the earth for aquifer investigations. Floating and towed transient electromagnetic (FloaTEM and tTEM) surveys provide resistivity soundings of the subsurface, which can be related to lithology and hydrogeology. In the TEM method, electrical current is cycled through a wire in a transmitter loop (Tx), which in turn produces a static magnetic field. When the current is abruptly terminated, an instantaneous current is induced in the earth, and it moves downward and outward as the induced current decays with time. The decay is controlled by the resistivity of the earth. A receiver (Rx) pulled behind the Tx loop measures the secondary magnetic field as a function of time (dB/dt). Decaying voltage measurements at the receiver are converted to apparent resistivity, which can be inverted to recover the depth-dependent resistivity structure of the earth. FloatTEM surveys were conducted at four locations on the Eel River near Falmouth, Massachusetts,on the Rainbow Reservoir near Windsor, Connecticut, on the Upper Delaware River near Barryville, New York, and on the Tallahatchie River in Shellmound, Mississippi. A tTEM survey was collected adjacent to the Tallahatchie River in Shellmound, Mississippi. The data collected at each site are provided as separate datasets. This data release includes the averaged, culled and inverted TEM data showing resistivity (in ohm-meters) with depth for each of the survey sites.

Surface and water-borne geophysical methods can provide information for the characterization of the subsurface structure of the earth for aquifer investigations. Floating and towed transient electromagnetic (FloaTEM and tTEM) surveys provide resistivity soundings of the subsurface, which can be related to lithology and hydrogeology. In the TEM method, electrical current is cycled through a wire in a transmitter loop (Tx), which in turn produces a static magnetic field. When the current is abruptly terminated, an instantaneous current is induced in the earth, and it moves downward and outward as the induced current decays with time. The decay is controlled by the resistivity of the earth. A receiver (Rx) pulled behind the Tx loop measures the secondary magnetic field as a function of time (dB/dt). Decaying voltage measurements at the receiver are converted to apparent resistivity, which can be inverted to recover the depth-dependent resistivity structure of the earth. FloatTEM surveys were conducted at four locations on the Eel River near Falmouth, Massachusetts,on the Rainbow Reservoir near Windsor, Connecticut, on the Upper Delaware River near Barryville, New York, and on the Tallahatchie River in Shellmound, Mississippi. A tTEM survey was collected adjacent to the Tallahatchie River in Shellmound, Mississippi. The data collected at each site are provided as separate datasets. This data release includes the averaged, culled and inverted TEM data showing resistivity (in ohm-meters) with depth for each of the survey sites.

The electrical conductivity of the earth is used to help infer lithological and pore fluid properties. Various geophysical methods can provide estimates of the distribution of below ground electrical conductivity, with each method having certain limitations. This data release presents raw and processed results from hand-caried frequency domain electromagnetic induction imaging (EMI) data collected from June 27-28 along Blacktail Creek near Williston, North Dakota. Data were primarily collected by walking in the creek or along the riparian zones with the GEM-2 instrument (Geophex, Ltd.) at approximately 0.5 m off the ground in horizontal coplanar (ski flat) mode.

The electrical conductivity of the earth is used to help infer lithological and pore fluid properties. Various geophysical methods can provide estimates of the distribution of below ground electrical conductivity, with each method having certain limitations. This data release presents raw and processed results from hand-caried frequency domain electromagnetic induction imaging (EMI) data collected from June 27-28 along Blacktail Creek near Williston, North Dakota. Data were primarily collected by walking in the creek or along the riparian zones with the GEM-2 instrument (Geophex, Ltd.) at approximately 0.5 m off the ground in horizontal coplanar (ski flat) mode.

When water is pumped slowly from saturated sediment-water inteface sediments, the more highly connected, mobile porosity domain is prefferentially sampled, compared to less-mobile pore spaces. Changes in fluid electrical conductivity (EC) during controlled downward ionic tracer injections into interface sediments can be assumed to represent mobile porosity dynamics, which are therefore distinguished from less-mobile porosity dynamics that is measured using bulk EC geoelectrical methods. Fluid EC samples were drawn at flow rates similar to tracer injection rates to prevent inducing preferential flow. The data were collected using a stainless steel tube with slits cut into the bottom (USGS MINIPOINT style) connected to an EC meter via c-flex or neoprene tubing, and drawn up through the system via a peristaltic pump. The data were compiled into an excel spreadsheet and time corrected to compare to bulk EC data that were collected simultaneously and contained in another section of this data release. Controlled, downward flow experiments were conducted in Dual-domain porosity apparatus (DDPA). Downward flow rates ranged from 1.2 to 1.4 m/d in DDPA1 and at 1 m/d, 3 m/d, 5 m/d, 0.9 m/d as described in the publication: Briggs, M.A., Day-Lewis, F.D., Dehkordy, F.M.P., Hampton, T., Zarnetske, J.P., Singha, K., Harvey, J.W. and Lane, J.W., 2018, Direct observations of hydrologic exchange occurring with less-mobile porosity and the development of anoxic microzones in sandy lakebed sediments, Water Resources Research, DOI:10.1029/2018WR022823.