Airborne Electromagnetic Surveys for 3 D Geological Mapping

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Airborne Electromagnetic Surveys for 3 -D Geological Mapping Jared D. Abraham and James C.

Airborne Electromagnetic Surveys for 3 -D Geological Mapping Jared D. Abraham and James C. Cannia

Project Sponsors North Platte Natural Resources District South Platte Natural Resources District Twin Platte

Project Sponsors North Platte Natural Resources District South Platte Natural Resources District Twin Platte Natural Resources District Nebraska Environmental Trust Nebraska Geological Survey

Project Contributors Jared D. Abraham James C. Cannia Bruce D. Smith Burke J. Minsley

Project Contributors Jared D. Abraham James C. Cannia Bruce D. Smith Burke J. Minsley Paul A. Bedrosian Steven S. Sibray Lyndsay B. Ball Michaela R. Johnson Maria Deszcz-Pan J. Alton Anderson Brian H. Imig

Study Location and Groundwater Models in the Area

Study Location and Groundwater Models in the Area

Motivation for Enhancing Hydrogeologic Frameworks • Difficult models, failure to converge/calibration issues due to

Motivation for Enhancing Hydrogeologic Frameworks • Difficult models, failure to converge/calibration issues due to poor geologic control • Poorly estimated bedrock topography despite large amounts of borehole and surficial geologic data • Groundwater quality will be better understood with new interpretations of geology • Understanding of groundwater age-dating information can be improved and used to calibrate model with new interpretation

Geology and Lithology A. Iron-stained sediments B. Manganese-stained sediments C. Siltstone clasts ~1. 5

Geology and Lithology A. Iron-stained sediments B. Manganese-stained sediments C. Siltstone clasts ~1. 5 feet in diameter Cross bedded, fluvial, coarse grained sediments of the Pliocene Broadwater Formation Photo taken ~1. 5 miles north of Big Springs, Nebraska, facing west A. Tertiary Brule fractures B. Unfractured Tertiary Brule Photo taken along summit road between tunnels 1 and 2, Scottsbluff National Monument, facing east.

Airborne Electromagnetic Survey Sky. TEM Time Domain EM System Fugro Resolve Frequency Domain EM

Airborne Electromagnetic Survey Sky. TEM Time Domain EM System Fugro Resolve Frequency Domain EM System

Location of Airborne EM Surveys

Location of Airborne EM Surveys

Inversion of EM data

Inversion of EM data

Electrical Properties High Resistivity – Red (80 to 500 ohm-m) • sand or gravels

Electrical Properties High Resistivity – Red (80 to 500 ohm-m) • sand or gravels (aquifer) Low Resistivity – Blue (5 to 30 ohm-m) • clays and silts (aquitard) Many combinations exist

Interpretation of EM Inversions (displayed as 2 -D Section)

Interpretation of EM Inversions (displayed as 2 -D Section)

3 -D EM Inversions and Interpretations

3 -D EM Inversions and Interpretations

Refined Base of Aquifer Contours

Refined Base of Aquifer Contours

Results of Interpretation (displayed as 2 -D section)

Results of Interpretation (displayed as 2 -D section)

Selected Sections from 3 -D Model

Selected Sections from 3 -D Model

Impact of 3 -D Model Refined 3 -D hydrogeological model Refined estimate of saturated

Impact of 3 -D Model Refined 3 -D hydrogeological model Refined estimate of saturated thickness Refined estimate of flow paths Refined estimation of surface and groundwater interaction

Selected Sections from the 3 -D Geological Model

Selected Sections from the 3 -D Geological Model

Change in Saturated Thickness New Saturated Thickness Previous Saturated Thickness

Change in Saturated Thickness New Saturated Thickness Previous Saturated Thickness

For the area of the airborne geophysical surveys, an additional ~3. 7 million acre-feet

For the area of the airborne geophysical surveys, an additional ~3. 7 million acre-feet of water in storage was identified

CONTACT INFORMATION Jared D. Abraham (303) 236 -1318 e-mail: jdabraha@usgs. gov USGS Crustal Imaging

CONTACT INFORMATION Jared D. Abraham (303) 236 -1318 e-mail: [email protected] gov USGS Crustal Imaging and Characterization Team (303) 236 -1213 Denver Federal Center, Bldg. 20, Box 25046, MS 964, Denver, CO 80225 -0046 http: //crustal. usgs. gov/ James C. Cannia (402) 416 -5321 e-mail: [email protected] gov USGS Nebraska Water Science Center (402) 328 -4100 5231 South 19 th St. , NE 68512 -1271 http: //ne. water. usgs. gov. Lincoln