Tracking changes in bulk electrical conductivity (EC) during tracer tests in saturated sediments allows for direct observation of both mobile and less-mobile pore space exchange dynamics. Electrode arrays made up of four stainless steel rods (insulated with the exception of exposed 0.5 cm tips) were installed vertically at depths of interest and apparent electrical resistivity data (the inverse of bulk EC) were collected using a Wenner configuration with an AGI SuperSting R8 meter. The Bulk EC data are described and listed within the files below. 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.

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.

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.

Quantification of mobile/less-mobile porosity dynamics at the sediment/water interface is critical to predicting contaminant storage, release, and transformation processes. Zones in groundwater flow-through lakes where lake water recharges the aquifer can strongly control aquifer water quality. Less-mobile porosity has previously been characterized in aquifers using flow path scale (10's of m+) tracer injections which are analyzed using numerical models. Methodology was recently developed to couple geoelectric measurements (bulk electrical conductivity, EC), which are directly sensitive to less-mobile ionic tracer exchange processes, with pumped fluid EC tracer data over time. If the fluid EC concentration history is assumed to reflect the more mobile porosity exchange processes, these paired fluid and bulk EC measurements can be used to quantify less-mobile porosity exchange in discrete cm-scale packets of sediment at the interface between surface and groundwater. For this study, tracer experiments were conducted in multiple rate-controlled downward flow experiments over several days. Although the bed was composed predominantly of highly permeable sands and gravels, which is not an intuitive sediment texture for less-mobile porosity, embedded cobbles created areas of less-mobile flow zones proximal to large cobbles. These experimental findings are described in detail in the associated 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.

Quantification of mobile/less-mobile porosity dynamics at the sediment/water interface is critical to predicting contaminant storage, release, and transformation processes. Zones in groundwater flow-through lakes where lake water recharges the aquifer can strongly control aquifer water quality. Less-mobile porosity has previously been characterized in aquifers using flow path scale (10's of m+) tracer injections which are analyzed using numerical models. Methodology was recently developed to couple geoelectric measurements (bulk electrical conductivity, EC), which are directly sensitive to less-mobile ionic tracer exchange processes, with pumped fluid EC tracer data over time. If the fluid EC concentration history is assumed to reflect the more mobile porosity exchange processes, these paired fluid and bulk EC measurements can be used to quantify less-mobile porosity exchange in discrete cm-scale packets of sediment at the interface between surface and groundwater. For this study, tracer experiments were conducted in multiple rate-controlled downward flow experiments over several days. Although the bed was composed predominantly of highly permeable sands and gravels, which is not an intuitive sediment texture for less-mobile porosity, embedded cobbles created areas of less-mobile flow zones proximal to large cobbles. These experimental findings are described in detail in the associated 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.

In June 2017, U.S. Geological Survey (USGS) collected geophysical measurements to help map variations in electrical properties to infer shallow flowpaths and storage zones influenced by residual spilled unconventional oil and gas (UOG). Two survey profiles were collected, each including dipole-dipole and Wenner-Schlumberger configurations. For each survey a total of 56 electrodes spaced 1.0 meter (m) apart were used. During the ERT measurement, current is injected through two current electrodes and voltage is measured sequentially across multiple pairs of potential electrodes; the known current and the measured voltages are used to determine the apparent resistivity of the subsurface. Inverse modeling of ERT survey results provide profiles of resistivity that can be interpreted for subsurface layers. This data release provides the raw ERT data and output from inversion.

In June 2017, U.S. Geological Survey (USGS) collected geophysical measurements to help map variations in electrical properties to infer shallow flowpaths and storage zones influenced by residual spilled unconventional oil and gas (UOG). Two survey profiles were collected, each including dipole-dipole and Wenner-Schlumberger configurations. For each survey a total of 56 electrodes spaced 1.0 meter (m) apart were used. During the ERT measurement, current is injected through two current electrodes and voltage is measured sequentially across multiple pairs of potential electrodes; the known current and the measured voltages are used to determine the apparent resistivity of the subsurface. Inverse modeling of ERT survey results provide profiles of resistivity that can be interpreted for subsurface layers. This data release provides the raw ERT data and output from inversion.

In order to test hypotheses about groundwater flow under and into estuaries and the Atlantic Ocean, geophysical surveys, geophysical probing, submarine groundwater sampling, and sediment coring were conducted by U.S. Geological Survey (USGS) scientists at Cape Cod National Seashore (CCNS) from 2004 through 2006. Coastal resource managers at CCNS and elsewhere are concerned about nutrients that are entering coastal waters via submarine groundwater discharge, which are contributing to eutrophication and harmful algal blooms. The research carried out as part of the study described here was designed, in part, to help refine assumptions required by earlier versions of models about the nature of submarine groundwater flow and discharge at CCNS. This study was conducted in four phases, with a variety of field techniques and equipment employed in each phase. Phase 1 consisted of continuous resistivity profiling (CRP) surveys of the entire study area conducted in 2004. Phase 2 consisted of CRP ground-truthing via resistivity probe measurements and submarine groundwater sampling from hydraulically-drive piezometers using a barge in the Salt Pond/Nauset Marsh area in 2005. Phase 3 consisted of supplemental detailed CRP surveys in the Salt Pond/Nauset Marsh area in 2006. Finally, Phase 4 consisted of sediment coring and porewater extraction in the Salt Pond/Nauset Marsh area later in 2006 to supplement the 2005 sampling.

In order to test hypotheses about groundwater flow under and into estuaries and the Atlantic Ocean, geophysical surveys, geophysical probing, submarine groundwater sampling, and sediment coring were conducted by U.S. Geological Survey (USGS) scientists at Cape Cod National Seashore (CCNS) from 2004 through 2006. Coastal resource managers at CCNS and elsewhere are concerned about nutrients that are entering coastal waters via submarine groundwater discharge, which are contributing to eutrophication and harmful algal blooms. The research carried out as part of the study described here was designed, in part, to help refine assumptions required by earlier versions of models about the nature of submarine groundwater flow and discharge at CCNS. This study was conducted in four phases, with a variety of field techniques and equipment employed in each phase. Phase 1 consisted of continuous resistivity profiling (CRP) surveys of the entire study area conducted in 2004. Phase 2 consisted of CRP ground-truthing via resistivity probe measurements and submarine groundwater sampling from hydraulically-drive piezometers using a barge in the Salt Pond/Nauset Marsh area in 2005. Phase 3 consisted of supplemental detailed CRP surveys in the Salt Pond/Nauset Marsh area in 2006. Finally, Phase 4 consisted of sediment coring and porewater extraction in the Salt Pond/Nauset Marsh area later in 2006 to supplement the 2005 sampling.

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.