DRAFT Adam Pidlisecky University of Calgary Tara Moran Stanford - - PowerPoint PPT Presentation

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DRAFT Adam Pidlisecky University of Calgary Tara Moran Stanford - - PowerPoint PPT Presentation

Jan 04, 2023 371 likes •622 views

Looking Beneath a Saltwater Intrusion: Geophysics for Improved Groundwater Management DRAFT Adam Pidlisecky University of Calgary Tara Moran Stanford University Rosemary Knight Stanford University The Center for Groundwater Evaluation and

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Looking Beneath a Saltwater Intrusion:

Geophysics for Improved Groundwater Management

Adam Pidlisecky

University of Calgary

Tara Moran

Stanford University Rosemary Knight Stanford University

The Center for Groundwater Evaluation and Management Stanford University

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Goal: To foster integration of new and emerging technologies into local, regional and statewide groundwater management practice. Approach: Partnering with with groundwater management districts throughout the western US to demonstrate the value

  • f these technologies.
The Center for Groundwater Evaluation and Management Stanford University

gemcenter.stanford.edu

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# # # #

Marina Seaside Monterey Pacific Grove Data courtesy of the California Geological Survey; Provided by the AZGS

^

Description of Map Symbols Cities 2011 ERT data 2012 ERT data

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SBWM well locations Cross section Seaside basin boundary ActiveFault Historic (<150 yrs) Holocene (<10 ka) Late Quaternary (<750 ka) Late Pleistocene (<1.6 ma) Early Pleistocene (<2.8 ma) Quaternary (Undifferentiated) Fault Monterey Bay

¹

5 2.5 Kms SBWM 1 SBWM 2 SBWM 3 SBWM 4 Monterey County Active Faults A' A

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Borehole based monitoring for Saltwater intrusion

¤ Sentinel Wells 2007 ¤ 4 monitoring wells drilled to facilitate time-lapse logging

  • f the aquifer to identify saltwater intrusion zones

¤ Wells drilled to ~ 300-400m ¤ Logged seasonally using resistivity logging –WHY?" ¤ Not really early warning! Once we see it in the well it is there. DRAFT

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SLIDE 6 Cross-bedded sand Well-graded sand Clay Depth (m) 20
  • 20
  • 60
  • 80
  • 40
DUNE SAND AQUIFER AROMAS SAND AQUIFER PASO ROBLES AQUIFER PASO ROBLES AQUIFER SBWM #3 SBWM #2 SBWM #1 SEASIDE BASIN SALINAS BASIN SBWM #4

N

A’ A

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modified after Feeney 2009

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Why resistivity?

  • Electrical Resistivity Tomography (ERT)
  • Well documented for small-scale water

resource applications

  • Currently used in petroleum applications – this

has lead to advancement in field systems and processing approaches

  • Non-invasive, fast deployment, continuous

data

  • 2D, 3D, and 4D imaging is possible

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What You’re Measuring: Resistivity (Ohm-m)

¤ Resistivity is a function

  • f the bulk electrical

properties and is sensitive to:

¤ porosity ¤ connectivity of pore fluid ¤ pore fluid chemistry ¤ lithology

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Pore fluid chemistry: Salinity

Concentration (g/L) ¡ Conductivity (S/m) ¡ Resistivity (Ohm-m) ¡ 0.03 ¡ 0.006 ¡ 156 ¡ 0.1 ¡ 0.02 ¡ 48 ¡ 0.3 ¡ 0.06 ¡ 16 ¡ 1 ¡ 0.2 ¡ 5 ¡ 3 ¡ 0.6 ¡ 2 ¡ 10 ¡ 1.8 ¡ 1 ¡

Saltwater Freshwater

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SLIDE 10 ρw

Concept of Operation

P1 P2 C1 C2

Volt Meter Current Meter Current Source

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  • We use multiple sensors (electrodes)

to make 10’s of thousands measurements

  • Each measurement samples a

different volume of earth

  • A typical array length for this work

will be ~ 1km, and will be shifted in 200m increments

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Like medical tomography, but with much poorer resolution

http://www.ablesw.com

Geophysical Tomography

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Geophysical Tomography

data (d)

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Data acquisition/ Processing

Two field campaigns:

¤ July 2011 ¤ October 2012 ¤ Total field days ~10

Total survey length: 6.8km Total number of data acquired: 130,000 Spatial resolution of inversion mesh: x: 10m, z: 5à10m Acquisition Cost: $60,000

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N

~8.5km ~8 5km

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~9km

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Conclusions

¤ Effective non-invasive subsurface imaging ¤ Improved large-scale understanding of aquifers ¤ Improved operational modeling ¤ Optimized remediation or interventions ¤ Lower cost and environmental impact ¤ Potential for long-term, spatially exhaustive monitoring

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Acknowledgments

¤ Brad Hansen, Curtis Ferguson, Andrew Parsekian, Jan Walbrecker, Nick Odlum, Jackie Randell ¤ Stephen Bachman at California State Parks- Monterey Division ¤ Tim Jensen at Monterey Peninsula Regional Parks ¤ Ben Mirus and Kim Perkins, USGS

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