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TVA Airborne EM Geophysics Presentation
	ML25345A482
Person / Time
Site:	Bellefonte, Clinch River, 05000615
Issue date:	12/12/2025
From:	Rucker D; hydroGEOPHYSICS
To:	; Office of Nuclear Reactor Regulation
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	Download: ML25345A482 (0)
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Dale Rucker, hydroGEOPHYSICS, Inc Helicopter-based Electromagnetic Imaging of Clinch River and Bellefonte Nuclear Sites

Subsurface Imaging and Innovative Solutions Why Geophysics?

There are only a few ways to interrogate the earth

Geophysics offers an inexpensive, rapid, and non-intrusive view of the subsurface

Airborne geophysics can deploy a variety of tools without terrain or vegetation issues

Cover up to 200 miles per day

Investigate to depths that exceed 1000 ft.

Subsurface Imaging and Innovative Solutions What is Electromagnetic Geophysics

Electromagnetics relies on induction

Alternating current in a transmitting loop

Primary magnetic field penetrates the earth, finds conductive bodies

New electrical current generated in the body, emits secondary magnetic field

Receiver loop measures the strength of the secondary magnetic field

The data are modeled as 1-D soundings of resistivity vs depth.

Subsurface Imaging and Innovative Solutions Schematic, Data, Model

Subsurface Imaging and Innovative Solutions Electrical Properties of Earth Materials

Subsurface Imaging and Innovative Solutions Scope for the Two Sites Clinch River (CRN)

Bellefonte (BLN)

Subsurface Imaging and Innovative Solutions Remaining Data (after noise removal)

Clinch River (CRN)

Bellefonte (BLN)

Subsurface Imaging and Innovative Solutions Geology Clinch River (CRN)

Bellefonte (BLN)

Subsurface Imaging and Innovative Solutions CRN Site Horizontal Slices

Subsurface Imaging and Innovative Solutions CRN Site Horizontal Slices - Area 1

Subsurface Imaging and Innovative Solutions CRN Site Profiles

Subsurface Imaging and Innovative Solutions CRN - Geological Cross Section

Subsurface Imaging and Innovative Solutions CRN - Summary

Surficial low-resistivity cover following the Clinch River and its terraces, approximately 1 to 11 meters deep. In the western area, the lower resistivity values are attributed to backfilled spoil material consisting of high plasticity clays and organic materials. The same area has slightly elevated resistivity, which is likely crushed limestone.

A persistent low-resistivity bedrock marker that was between 50 and 100 ohm-m correlated to the Blackford/Lincolnshire Fm. This band steepens toward the northwest and migrates southeast with depth, providing a structural datum that matches the mapped bedding and the Chestnut Ridge fault trend noted on site geological map.

Resistive, competent bedrock in Area 2, 10,000 ohm-m was consistent with Knox Group dolomite at depth and at higher elevations. This unit imposes a shallow DOI in the north due to high resistivity, limiting confidence below 45 to 65 meters.

Deeper conductivity increases to the southeast is consistent with Witten/Benbolt argillaceous carbonates and calcareous shales.

Profile Set 1 indicates offset/warping of the conductive marker at the southeastern ends of several profiles, potentially suggesting one or more buried faults or shear zones subparallel to strike. The overlay with the geologic cross-section shows good stratigraphic concordance, with local departures at marked features (A-D) that may reflect alteration.

Subsurface Imaging and Innovative Solutions CRN - Recommendations

New borings / hydro tests:

Two across the low-resistivity Blackford/Lincolnshire band (one near MP-412 corridor) to verify lithology, clay content, fracture density, and water levels.

Two within resistive Area 2 to quantify rock quality (RQD), karst risk, and depth to competent bearing strata.

Two straddle-fault tests across the suspected offsets in Profile Set 1 (Fig. 61) to confirm displacement and measure fracture permeability.

Additional geophysics

Downhole logging

ERT at missing AEM soundings (due to noise) and in Area 2 below the 45m DOI

Subsurface Imaging and Innovative Solutions BLN Site Horizontal Slices

Subsurface Imaging and Innovative Solutions BLN Profile Locations

Subsurface Imaging and Innovative Solutions Profile Set 1

Subsurface Imaging and Innovative Solutions Profile Set 2

Subsurface Imaging and Innovative Solutions Profile Set 3

Subsurface Imaging and Innovative Solutions Profile Set 4

Subsurface Imaging and Innovative Solutions Profile Set 5

Subsurface Imaging and Innovative Solutions Profile 5 with Borings

Subsurface Imaging and Innovative Solutions BLN Summary

Stratigraphic framework dominated by Paleozoic carbonates of the Knox and Chickamauga Groups, overlain locally by Mississippian and Pennsylvanian formations,

Quaternary alluvium and terrace deposits observed along the Tennessee River margins.

The resistivity data successfully delineated alternating high-and low-resistivity bands that correspond to mapped geological formations, paleochannels, and terrace deposits,

The data generally highlighted the extents of karst-prone carbonates and alluvial infill.

However, karst itself was not explicitly identified in the resistivity data.

Vertical profiles confirmed southeast-dipping bedding consistent with regional structure,

The overall dataset showed no evidence of major hidden faults or structural disruptions beneath the plant site.

Comparison with existing borehole data further validated the correspondence between resistivity contrasts and lithological variations of the Upper Stones River Group.

Subsurface Imaging and Innovative Solutions Recommendations

Targeted ground truthing with five to eight borings placed along key resistivity boundaries, for example at the Knox-Nashville/SR or Sequatchie/Red Mountain contacts, terrace/alluvium margins in order to pin lithology and weathering depth.

Collect petrophysical samples for lab resistivity, porosity, and clay content to reduce uncertainty in the AEM-to-lithology correspondence.

Downhole geophysics in new or existing wells to potentially include optical or acoustic televiewer to map bedding and fractures, NMR logging to distinguish bound water from mobile water layers, and gamma to distinguish shale thickness and quality.

Seismic screening with MASW to correlate shear velocity with AEM layering, and flag zones of soft sediments or weathered karst residuum.

Subsurface Imaging and Innovative Solutions Recommendations (lower-tier priority)

High-density electrical resistivity tomography (ERT) and induced (IP) transects to map karst-prone carbonates and terrace/alluvium margins to image voided or weathered zones along with clayey horizons seen as conductive layers in the AEM data. The ERT would also be used to fill in gaps of the AEM data.

Microgravity grids over karst-suspect areas to detect meter-sized density deficits that would be indicative of voids or sinkholes where AEM shows anomalously high resistivity and thin cover.

ML25345A482

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