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Person

Lance R Gruhn

Hydrologist
Office of the Chief Operating Officer

Email: lgruhn@usgs.gov
Office Phone: 319-358-3631
ORCID: 0000-0002-7120-3003

Location
Federal Building
400 S Clinton St Rm 269
Iowa City , IA 52240

Supervisor: Timothy D Straub
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These data were collected in coordination with the U.S. Geological Survey Hydrogeophysics Branch for the National Crude Oil Spill Fate and Natural Attenuation Research Site. Water quality data were collected using an Ecomapper Autonomous Underwater Vehicle (AUV) and measured parameters include temperature, specific conductance, salinity, water density, pH, dissolved oxygen, total chlorophyll, and blue-green algae. These data are provided in two formats: a CSV file named AUV_WQ_South.csv, and in the Environmental Systems Research Institute (ESRI) shapefile format consisting of a group of files that have been compressed into a zip archive that is named AUV_WQ_South_shapefile.zip.
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In summer 2018, a total of 43 passive seismic surveys were conducted in the Des Moines River floodplain. The horizontal-to-vertical spectral ratio (HVSR) method is a passive seismic technique that uses a three-component seismometer to measure the vertical and horizontal components of ambient seismic noise. A resonance frequency (f0) is induced in the unconsolidated deposits when there is a substantial contrast (greater than 2:1) in shear-wave acoustic impedance between the overburden and the bedrock. The f0 is determined from the analysis of the spectral ratio of the horizontal and vertical components of the seismic data. The thickness of the overburden can be related to the f0. In general, lower f0 relates to thicker...
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Geophysical Data Collected in the Des Moines River, Beaver Creek, and the Des Moines River Floodplain, Des Moines, Iowa, 2018
A suite of geophysical methods was used along the Des Moines River, Beaver Creek, and in the Des Moines River floodplain in Des Moines, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river. The aquifer consists of sands and gravels underlain by weathered shale bedrock. Groundwater from the aquifer along with surface water sources are used for municipal drinking water for the City of Des Moines and surrounding communities. The raw data provided in this data release are minimally processed to filter out erroneous measurements. Data provided in this data release includes continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) that were collected...
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Electrical resistivity tomography (ERT) surveys were collected in summer 2018 to support hydrogeologic characterization of the alluvial aquifer. For this investigation, 7 surveys were conducted with ERT methods. At each site three surveys were collected, including dipole-dipole (DD), Wenner-Schlumberger (WS), and Inverse Schlumberger (SI )configurations. For each survey a total of 56 electrodes spaced 5-meters (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, which is used to determine the apparent resistivity of the subsurface. Results were combined into a merged dataset. ERT surveys...
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Geophysical Data Collected in the Cedar River Floodplain, Cedar Rapids, Iowa, 2015-2017
A suite of geophysical methods was used along the Cedar River in Cedar Rapids, Iowa to support the hydrogeologic characterization of the alluvial aquifer associated with the river and to assess the area for suitability for larger-scale airborne geophysics. The aquifer is comprised of sand and gravel, interbedded with finer sediments, and underlain by carbonate-dominated bedrock. The aquifer is the principal source of municipal drinking water for the City of Cedar Rapids. The raw data provided here includes waterborne continuous resistivity profiling (CRP) and continuous seismic profiling (CSP) data (collected at the same time), electrical resistivity tomography (ERT) profiles, and horizontal-to-vertical spectral...
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