Aquifer Imaging with Oscillatory Hydraulic Tomography: Application at the Field Scale

Area of Science:

• Geosciences
• Hydrogeology
• Geophysics

Background:

• Aquifer characterization is crucial for groundwater management.
• Traditional hydraulic tomography methods can be labor-intensive and involve significant water exchange.
• Oscillatory hydraulic tomography (OHT) offers a promising alternative for detailed aquifer property assessment.

Purpose of the Study:

• To report the first field application of Oscillatory Hydraulic Tomography (OHT).
• To assess the efficacy of OHT in characterizing aquifer hydraulic properties at the Boise Hydrogeophysical Research Site (BHRS).
• To compare OHT results with existing characterization data from the BHRS.

Main Methods:

• Utilized an oscillating signal generator with a small cycling volume (<2 L) and periods ranging from 5 to 70 seconds.
• Measured head signals at multiple monitoring locations to detect oscillations up to 15 meters away.
• Employed frequency-domain numerical modeling for groundwater flow to perform tomography on extracted periodic signal properties.

Main Results:

• Successfully detected oscillatory signals at distances exceeding 15 meters.
• Demonstrated moderate to strong positive correlations between hydraulic conductivity (K) profiles estimated by OHT and prior methods at multiple wells.
• Achieved moderate overall correlation for estimated three-dimensional (3D) K volumes.

Conclusions:

• The first field application confirms OHT's capability to characterize aquifer heterogeneity.
• OHT provides a non-invasive method with a clear, extractable signal, suitable for noisy environments.
• OHT results show good agreement with established characterization techniques, validating its potential for practical hydrogeophysical investigations.