Airborne Electromagnetic Surveys for 3 D Geological Mapping
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 Natural Resources District Nebraska Environmental Trust Nebraska Geological Survey
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
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 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 System
Location of Airborne EM Surveys
Inversion of EM data
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)
3 -D EM Inversions and Interpretations
Refined Base of Aquifer Contours
Results of Interpretation (displayed as 2 -D section)
Selected Sections from 3 -D Model
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
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 of water in storage was identified
CONTACT INFORMATION Jared D. Abraham (303) 236 -1318 e-mail: jdabraha@usgs. 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: jcannia@usgs. gov USGS Nebraska Water Science Center (402) 328 -4100 5231 South 19 th St. , NE 68512 -1271 http: //ne. water. usgs. gov. Lincoln
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