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 land-based and water-based frequency domain electromagnetic induction (EMI) data collected from August 23, 2017 to August 28, 2017. The raw data consist of .csv files from the Geophex GEM-2 unit. Data were primarily collected by walking with the instrument at approximately 1 m off the ground in horizontal coplanar (ski flat) mode. A survey along a section of the Little Wind River in a kayak (with about 0.3 m of elevation above the water surface) was also collected.

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 land-based and water-based frequency domain electromagnetic induction (EMI) data collected from August 23, 2017 to August 28, 2017. The raw data consist of .csv files from the Geophex GEM-2 unit. Data were primarily collected by walking with the instrument at approximately 1 m off the ground in horizontal coplanar (ski flat) mode. A survey along a section of the Little Wind River in a kayak (with about 0.3 m of elevation above the water surface) was also collected.

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.

This data release contains geophysical data collected at the Little Wind River site near Riverton, Wyoming in 2015 and 2017. The dataset contains:[1] Fiber Optic Distributed Temperature Sensing data (FO-DTS, August-September 2015) collected in the water along the river bank, [2] Electrical Resistivity Tomography data (ERT, August 2017) collected on land near the river bank, and [3] Frequency domain Electromagnetic Induction (EMI, August 2017) data collected along the river and more extensively throughout the study region. Data for each of these methods can be found in the child items linked below.

This data release contains geophysical data collected at the Little Wind River site near Riverton, Wyoming in 2015 and 2017. The dataset contains:[1] Fiber Optic Distributed Temperature Sensing data (FO-DTS, August-September 2015) collected in the water along the river bank, [2] Electrical Resistivity Tomography data (ERT, August 2017) collected on land near the river bank, and [3] Frequency domain Electromagnetic Induction (EMI, August 2017) data collected along the river and more extensively throughout the study region. Data for each of these methods can be found in the child items linked below.

The Little Colorado River alluvial aquifer near Leupp, Arizona was investigated as a possible source of irrigation water for the Leupp and Birdsprings Chapters of the Navajo Nation. The physical, chemical, and hydraulic characteristics of the alluvial aquifer were studied using geophysical surveys, installation of observation wells, water-level measurements, chemical analyses, groundwater pumping simulations, and review of previous investigations. Geophysical surveys and well borings were used to measure the thickness of the aquifer. Geophysical surveys included Electrical Resistivity Tomography (ERT) to better define the alluvial channel of the Little Colorado River near Leupp. ERT is a commonly used electrical geophysical technique for investigating the subsurface of the Earth. In this study it was tested in two separate areas to determine how effective the technique would be for determining the thickness of the alluvial sediments along the LCR. An Advanced Geosciences Inc. Supersting R8TM multi-channel resistivity/IP meter with a SwitchBox56® was used for the DC resistivity survey and all DC resistivity survey data was modeled using Advanced Geosciences Inc. Earthimager 2D software. For each survey line, 56 electrodes were placed on the ground with a spacing of 5 meters (except Line MB4 had a spacing of 6 meters) for the initial survey segment and when the segment was completed then the first 28 electrodes of the survey were moved to the end of the survey line in a roll-along technique. The survey line can be extended indefinitely in a leap-frog fashion even though each segment is only 56 electrodes at a fixed spacing of 5 meters. Resistivity measurements were made in different arrangements or arrays of electrodes, and for this survey dipole-dipole and strong-gradient arrays were used. For both array types, an electrical current is transmitted into the ground, and the resulting potential differences are measured at the surface (Sharma, 1997). Layers within the Earth that are electrically conductive or resistive will deflect or distort the normal potentials.

The Little Colorado River alluvial aquifer near Leupp, Arizona was investigated as a possible source of irrigation water for the Leupp and Birdsprings Chapters of the Navajo Nation. The physical, chemical, and hydraulic characteristics of the alluvial aquifer were studied using geophysical surveys, installation of observation wells, water-level measurements, chemical analyses, groundwater pumping simulations, and review of previous investigations. Geophysical surveys and well borings were used to measure the thickness of the aquifer. Geophysical surveys included Electrical Resistivity Tomography (ERT) to better define the alluvial channel of the Little Colorado River near Leupp. ERT is a commonly used electrical geophysical technique for investigating the subsurface of the Earth. In this study it was tested in two separate areas to determine how effective the technique would be for determining the thickness of the alluvial sediments along the LCR. An Advanced Geosciences Inc. Supersting R8TM multi-channel resistivity/IP meter with a SwitchBox56® was used for the DC resistivity survey and all DC resistivity survey data was modeled using Advanced Geosciences Inc. Earthimager 2D software. For each survey line, 56 electrodes were placed on the ground with a spacing of 5 meters (except Line MB4 had a spacing of 6 meters) for the initial survey segment and when the segment was completed then the first 28 electrodes of the survey were moved to the end of the survey line in a roll-along technique. The survey line can be extended indefinitely in a leap-frog fashion even though each segment is only 56 electrodes at a fixed spacing of 5 meters. Resistivity measurements were made in different arrangements or arrays of electrodes, and for this survey dipole-dipole and strong-gradient arrays were used. For both array types, an electrical current is transmitted into the ground, and the resulting potential differences are measured at the surface (Sharma, 1997). Layers within the Earth that are electrically conductive or resistive will deflect or distort the normal potentials.

Surface electrical resistivity tomography (ERT), electromagnetic induction (EMI), and self-potential (SP) data were acquired March 9 - 20, 2018 by the U.S. Geological Survey (USGS), in collaboration with the U.S. Army Corps of Engineers (USACE), at the Jim Woodruff Lock and Dam near Chattahoochee, Florida. Eleven ERT profiles were acquired along the right (west) abutment, and immediately downstream, of the concrete, fixed-crest spillway located west of the lock to map geologic structure at depths up to 50 meters (m) using the Advanced Geosciences, Inc. SuperSting R8 resistivity meter. This data release includes the raw and processed resistivity data as well as inverted resistivity models. All are provided as digital data, and data fields for each file type are defined in the respective data dictionary (https://www.sciencebase.gov/catalog/item/5e101068e4b0b207aa163765). Jim Woodruff Lock and Dam is located on the Apalachicola River just south of the confluence of the Flint and Chattahoochee Rivers along the Florida-Georgia border. Construction was completed in 1954 and impounds Lake Seminole. The dam has a long history of excessive seepage along the right abutment and below the fixed-crest spillway. Several karst features have been mapped over the years including sinkholes, both on land and along the lake bottom, and disappearing and reappearing streams. Such features were excavated and grouted during construction. Despite years of investigation of the dam foundation, there remains uncertainty on the flowpaths of water below the fixed-crest spillway and along the adjacent right abutment. REFERENCE Abraham, J.D., Deszcz-Pan, M., Fitterman, D.V., and Burton, B.L., 2006, Use of a handheld broadband EM induction system for deriving resistivity depth images, in 19th Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Seattle, Washington, April 2–6, 2006, 18 p.

Electrical resistivity Tomography (ERT) is a direct current geophysical method that is used to estimate the subsurface distribution of the electrical resistivity (measured in ohm-meters, or ohm-m) of a material, and is based on the assumption that measured electric potentials (voltages) near current carrying electrodes are influenced by the electrical resistivities of the underlying material (Zohdy and others, 1974; Day-Lewis and others, 2008). Bulk resistivity is controlled by lithology, porosity, degree of saturation, chemistry of groundwater, and the conductivity of earth materials at the surface. If the degree of saturation is the only expected variable, as is the case near the groundwater replenishment and reuse project (GRRP) facility, groundwater infiltration paths can be identified with sequential ERT surveys. Data from two ERT surveys (YVHDWW_L1 and YVHDWW_L2) were collected orthogonal to each other in May and September of 2019 to determine background resistivity values downslope of the GRRP facility prior to release of reclaimed wastewater to the infiltration ponds. The resistivity data are presented in native *.stg format, as well as topographic data for each electrode in *.trn format.

Electrical resistivity Tomography (ERT) is a direct current geophysical method that is used to estimate the subsurface distribution of the electrical resistivity (measured in ohm-meters, or ohm-m) of a material, and is based on the assumption that measured electric potentials (voltages) near current carrying electrodes are influenced by the electrical resistivities of the underlying material (Zohdy and others, 1974; Day-Lewis and others, 2008). Bulk resistivity is controlled by lithology, porosity, degree of saturation, chemistry of groundwater, and the conductivity of earth materials at the surface. If the degree of saturation is the only expected variable, as is the case near the groundwater replenishment and reuse project (GRRP) facility, groundwater infiltration paths can be identified with sequential ERT surveys. Data from two ERT surveys (YVHDWW_L1 and YVHDWW_L2) were collected orthogonal to each other in May and September of 2019 to determine background resistivity values downslope of the GRRP facility prior to release of reclaimed wastewater to the infiltration ponds. The resistivity data are presented in native *.stg format, as well as topographic data for each electrode in *.trn format.