This data release contains electrical resistivity tomography (ERT) and frequency domain electromagnetic (FDEM) data collected in areas of unwalled shoreline at the Bremerton Naval Complex, WA, June 1-5, 2023. Preliminary inverse results from the FDEM data area also included. Two sites were investigated: Charleston Beach and Segment 4. Charleston Beach is a gently sloping pebble beach adjacent to the naval complex; whereas Segment 4 is a steeply sloping section of rocky shoreline on the naval complex surrounded by a pier and naval complex infrastructure. At Charleston Beach, FDEM data were collected with two different instruments with different sensitivity patterns (a DualEM-421 and a GEM-2) during negative tide (less than the mean low tide level) on June 2,2023. At Segment 4, various time-lapse ERT configurations were tested during June 3-5 over tidal cycles, while FDEM datasets (GEM-2 only) were collected during negative tides over this period. To facilitate comparison of geophysical data with tides, tide elevation predictions from NOAA station 9445958 are included in this release. A local digital elevation model was also created for Segment 4 using a real time kinematic (RTK) global positioning system.

Extending 200 kilometers (km) along the Atlantic Coast of Central Florida, Indian River Lagoon (IRL) is one of the most biologically diverse estuarine systems in the continental United States. The lagoon is characterized by shallow, brackish waters and a width that varies between 0.5 and 9.0 km; there is significant human development along both shores. Scientists from the U.S. Geological Survey (USGS) St. Petersburg Coastal and Marine Science Center used continuous resistivity profiling (CRP, a towed electronic array) measurements, electrical resistivity tomography (ERT), and basic physical water column properties (for example, depth and temperature) to investigate submarine groundwater discharge at two locations, Eau Gallie North and Riverwalk Park, along the western shore of IRL. Eau Gallie North is near the central section of IRL and Riverwalk Park is approximately 20 km north of the Eau Gallie site. At each CRP study site, an 11-electrode marine resistivity array was towed over seven north–south shore parallel transects (EA–EG and RA–RG, respectively), situated between 75–1000 meters offshore, and approximately 1.5 km in length. Each transect was mapped three times in an alternating north–south direction to account for data collected by the concurrently-operating radon mapping system (Everhart and others, 2018). Repeat streaming resistivity surveys were collected bimonthly along these same tracklines, between March and November 2017, to determine seasonal and temporal variability. Since resistivity is a function of both geology and salinity, it is assumed that temporal shifts will reflect salinity changes, as the underlying geology will be presumed to remain constant. ERT study areas consisted of land- and shallow water-based surveys, where [DC] electrical current was injected into the ground via two current electrodes and received by nine potential electrodes. Electrode positions for both sites were recorded along six transects (T01-T06) and are provided in this data release as supplemental information (please see the ERT location map files included in, ERT_survey_maps.zip).

In October 2016 and May 2017 frequency domain electromagnetic (FDEM) methods were used to image the electrical conductivity of the shallow subsurface. Electrical conductivity can be caused by changes in the soil, overburden, saturation, and water quality. Two multi-frequency tools were used at the site. One of the tools has a 1.6-meter (m) long antenna that was used in the vertical-dipole mode to collect data in stepped-frequency mode at seven user-selected frequencies ranging from 1530 to 47,970 Hertz (Hz). The GEM2HG tool has an antenna that is 2.1 m long, and it was used in vertical dipole mode with five stepped frequencies ranging from 90 to 24,000 Hz. In general, the lower frequencies penetrate to deeper depths, but the data are an average over a larger volume; whereas higher frequencies penetrate only to shallow depths but provide a smaller volume-averaged measurement. A plastic-pipe frame was used to keep the antenna at a fixed distance of 1.0 m above water surface to minimize noise induced by variation in tool position. Profiling data were collected at walking speeds of approximately 3 kilometer per hour(km/hr), with a full suite of seven frequencies measured every 0.5 seconds (s), which translates to a complete measurement suite about every 0.4 m along the profile. All measurement positions were mapped with a global positioning system (GPS). Both the primary and secondary fields were measured at the receiver coil, and the ratio of the secondary to primary magnetic fields was recorded as in-phase and quadrature. The in-phase part of the EM field relates to the magnetic susceptibility, and the quadrature component relates to apparent conductivity (aEC) . Raw data for each frequency and Q Sum (a summation of quadrature values) were recorded in parts per million (ppm). In post processing, EM data were converted to magnetic susceptibility and aEC, which can be inverted to get the actual depth of the electrical conductivity value. This data release provides the raw ppm values, the magnetic susceptibility, and the apparent electrical conductivity values.

In October 2016 and May 2017 frequency domain electromagnetic (FDEM) methods were used to image the electrical conductivity of the shallow subsurface. Electrical conductivity can be caused by changes in the soil, overburden, saturation, and water quality. Two multi-frequency tools were used at the site. One of the tools has a 1.6-meter (m) long antenna that was used in the vertical-dipole mode to collect data in stepped-frequency mode at seven user-selected frequencies ranging from 1530 to 47,970 Hertz (Hz). The GEM2HG tool has an antenna that is 2.1 m long, and it was used in vertical dipole mode with five stepped frequencies ranging from 90 to 24,000 Hz. In general, the lower frequencies penetrate to deeper depths, but the data are an average over a larger volume; whereas higher frequencies penetrate only to shallow depths but provide a smaller volume-averaged measurement. A plastic-pipe frame was used to keep the antenna at a fixed distance of 1.0 m above water surface to minimize noise induced by variation in tool position. Profiling data were collected at walking speeds of approximately 3 kilometer per hour(km/hr), with a full suite of seven frequencies measured every 0.5 seconds (s), which translates to a complete measurement suite about every 0.4 m along the profile. All measurement positions were mapped with a global positioning system (GPS). Both the primary and secondary fields were measured at the receiver coil, and the ratio of the secondary to primary magnetic fields was recorded as in-phase and quadrature. The in-phase part of the EM field relates to the magnetic susceptibility, and the quadrature component relates to apparent conductivity (aEC) . Raw data for each frequency and Q Sum (a summation of quadrature values) were recorded in parts per million (ppm). In post processing, EM data were converted to magnetic susceptibility and aEC, which can be inverted to get the actual depth of the electrical conductivity value. This data release provides the raw ppm values, the magnetic susceptibility, and the apparent electrical conductivity values.

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.

The bulk electrical conductivity of the subsurface was indirectly measured with electromagnetic imaging (EMI) by using induced secondary electromagnetic signals generated by subsurface electrical conductors in response to transmitted electromagnetic energy (Zohdy and others, 1974). Electromagnetic induction data were collected using a DUALEM-421 (DualEM, Inc.) mounted on an inflatable stand-up paddle board about 15 centimeters above the water surface. The DUALEM-421 uses 3 transmitter-receiver coil spacings (4-, 2-, and 1-meters) and 2 orientations (vertical dipole, and horizontal dipole). Larger coil spacings interrogate a larger/deeper sampling volume than smaller coil separations. REFERENCE: U.S. Geological Survey, Techniques of Water-Resources Investigations, Book 2, Chapter D1, Zhody, A. A. R., Eaton , G. P., and Mabey, D. R. https://doi.org/10.3133/twri02D1

The bulk electrical conductivity of the subsurface was indirectly measured with electromagnetic imaging (EMI) by using induced secondary electromagnetic signals generated by subsurface electrical conductors in response to transmitted electromagnetic energy (Zohdy and others, 1974). Electromagnetic induction data were collected using a DUALEM-421 (DualEM, Inc.) mounted on an inflatable stand-up paddle board about 15 centimeters above the water surface. The DUALEM-421 uses 3 transmitter-receiver coil spacings (4-, 2-, and 1-meters) and 2 orientations (vertical dipole, and horizontal dipole). Larger coil spacings interrogate a larger/deeper sampling volume than smaller coil separations. REFERENCE: U.S. Geological Survey, Techniques of Water-Resources Investigations, Book 2, Chapter D1, Zhody, A. A. R., Eaton , G. P., and Mabey, D. R. https://doi.org/10.3133/twri02D1

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.

The Santa Clara River Lakes, located along the San Andreas fault 19 miles northwest of Palmdale, California, were placed on the state’s “303(d) List” or “Impaired Water List” in 1996 for eutrophic conditions, high pH, and low dissolved oxygen. In 2016, the state adopted a Total Maximum Daily Load (TMDL) for nutrients (nitrogen and phosphorus) in the Santa Clara River Lakes. This study focuses on the largest of the three lakes, Lake Elizabeth, which is surrounded by the unincorporated town of Elizabeth Lake, CA. The local community uses on-site wastewater treatment systems instead of a centralized sewer system, resulting in potential contamination of groundwater. In response to concerns over the quality of water in the area and fluctuating water levels in Elizabeth Lake, the U.S. Geological Survey (USGS) cooperated with the Los Angeles Regional Water Quality Control Board to assess hydrologic conditions and water quality near Elizabeth Lake. As part of this work, the USGS did electrical resistivity tomography (ERT) survey lines at two locations across the southern edge of the lake near the community in March 2019.