Opening Remarks
 

1:05 - 1:25 p.m.

Advancing the Contaminated Subsurface Characterization with Pore-Scale Geoelectrical Developments

Flore Rembert, Ghent University

Geoelectrical methods are increasingly used as monitoring tools for contaminated sites. These methods are sensitive to petrophysical, transport, and interfacial properties that influence contaminant transport and remediation scenarios. However, interpreting the geoelectrical response remains challenging due to the inherent complexity and heterogeneity of geological media. Subsurface environments are composed of distinct, interacting compartments that interact at large scales while being supported by microscopic mechanisms. Therefore, the development of pore-scale studies, combining high-resolution observations with geoelectrical acquisition, offers promising outcomes for understanding, quantifying, and predicting geoelectrical signals. This talk will highlight recent experimental and modeling advances in geoelectrical monitoring for the mechanistic description of fluid flow involved in reactive transport and multiphase flow.

Coauthors: Hamdi Omar (Ghent University), Sophie Roman (University of Orleans), Tom Bultreys (Ghent University)

1:25 - 1:45 p.m.

Spectral Induced Polarization Signatures of Biochar

Dimitrios Ntarlagiannis, Rutgers University - Newark

Biochar, the carbon-rich product from the pyrolysis of biomass including agricultural waste, is a widely used soil amendment. Its unique surface properties also make it a powerful agent for environmental management, offering long-term stability and the potential to treat diverse contaminants. However, the widespread use of biochar for environmental applications is hampered by the lack of universal characterization and classification methods, inhomogeneity issues, and the absence of robust long-term monitoring schemes.

Currently, field-scale characterization and monitoring primarily rely on direct sampling and laboratory analysis which are time and cost inefficient. Geophysical methods, like spectral induced polarization (SIP), could provide real-time, in-situ characterization and monitoring with high spatial and temporal coverage, enabling informed decision-making (e.g. sampling time and location). SIP is an established geophysical method increasingly used in environmental applications. It offers unique advantages, particularly its sensitivity to interfacial properties, which can address key challenges in biochar's environmental applications, offering robust characterization and performance monitoring.

To investigate SIP's applicability for biochar characterization, we conducted column experiments using various biochar types, concentrations, particle sizes, and saturating fluid properties. Our initial results show that different biochar types produce measurable SIP responses with distinct characteristics. Interestingly, these responses do not appear to be dominated by biochar's surface characteristics (e.g., surface area), contrary to our initial hypotheses. Instead, our findings suggest behavior similar to that observed for graphite and/or metallic electron-conducting particles. These results strongly support further research into SIP as a technology for characterizing biochar and, subsequently, for real-time monitoring of soil remediation processes.

Coauthors: Jael Estrada (Rutgers University - Newark), Dimitris Kalderis (Hellenic Mediterranean University), Lee Slater (Rutgers University - Newark/PNNL)

1:45 - 2:05 p.m.

A Trial of Geoelectrical Methods for Leak Detection and Monitoring During Waste Retrievals from the Magnox Swarf Storage Silo, Sellafield, UK

Oliver Kuras, British Geological Survey

As waste retrievals from the Magnox Swarf Storage Silo (MSSS) at Sellafield are progressing towards the oldest parts of the structure, a key requirement is to implement a solution for the detection, mitigation and monitoring of any leak of silo liquor to ground as a result of retrieval operations. Due to limited physical access to the perimeter of MSSS and the additional risks associated with intrusive investigation, geophysical methodologies are being considered as the preferred approach for providing non-invasive information about subsurface processes below and near MSSS.

We describe a trial of the electrical resistivity tomography (ERT) and mise-à-la-masse (MALM) techniques using existing in-ground metallic infrastructure around MSSS as “long electrodes” to provide galvanic contact with the ground, thereby eliminating the need for excavation or drilling. Arrays of blind tubes from routine dose rate monitoring were utilised, along with additional earthing rods driven into the soil at shallow depth within existing borehole headworks. In-silo electrodes were placed in compartments of the oldest building to facilitate the MALM measurements.

Extensive ERT and MALM measurements in a variety of geometric configurations were undertaken over one week in late April 2025 and the resulting data analysed for their potential to help identify, locate and monitor any leaks from MSSS. MALM datasets were processed into maps of electrical potential surrounding MSSS, whereas ERT datasets were used to produce 3D models of subsurface electrical resistivity in the vicinity of the building. We present results of the trial and discuss the potential for implementing a long-term geoelectrical monitoring solution at MSSS to support retrievals over the next 25-30 years.

Coauthors: Paul Wilkinson, James Boyd, Yin Jeh Ngui, Harry Harrison, and Philip Meldrum (British Geological Survey); James Mair, Stephen Gregory, Nick Barnes, and John Heneghan (Sellafield, Ltd.)

2:05 - 2:25 p.m.

Integrated Use of Soil Radon Monitoring and Geophysical Methods for Fault Detection in a Hydrocarbon-Affected Area

César J. Guevara-Pillaca, Instituto Geológico, Minero y Metalúrgico

Detecting subsurface geological discontinuities is critical for understanding contaminant migration pathways and developing effective remediation strategies, particularly in hydrocarbon-impacted environments. This study investigates the integrated use of soil radon monitoring and geophysical methods to identify hidden faults beneath a site affected by surface hydrocarbon seepage, located within an educational facility. Geophysical techniques, including electrical resistivity and seismic methods, enabled the delineation of lithological sequences, saturated aquifers, and hydrocarbon-affected zones. Subvertical anomalies identified in the profiles were interpreted as potential fault zones. To validate and refine these interpretations—especially in areas obscured by surface infrastructure—soil radon measurements were performed. Elevated radon concentrations spatially correlated with the previously inferred structural discontinuities, suggesting enhanced permeability typically associated with fault-related pathways. Complementary permeability tests were conducted to calibrate radon flux data, thereby improving the reliability and interpretative power of the radon surveys. The integration of radioactive gas measurements with geophysical data provided a more detailed and coherent picture of subsurface conditions. This combined approach not only improved the detection and characterization of concealed faults but also proved particularly effective in settings with restricted access or surface obstructions. The results underscore the utility of radon as a noninvasive, sensitive, and cost-efficient tracer for subsurface structural features. This methodology offers a robust framework for environmental site assessments, particularly in complex hydrogeological contexts where fault zones may influence contaminant dispersion. Ultimately, the study supports the inclusion of soil radon monitoring as a valuable complement to geophysical surveys in fault detection and environmental remediation planning.

Coauthors: Briant García (Instituto Geológico, Minero y Metalúrgico), Bertin Pérez (Anphysrad SAC), Rafael Ponce-Amanca (Anphysrad SAC)

Open Discussion
 

BREAK
 

3:15 - 3:35 p.m.

A Lightweight, Flexible, Multitask AI Pipeline for Geophysical Inversion

R. Amzi Jeffs, Pacific Northwest National Laboratory

We develop novel AI algorithms for geophysical inversion. Our training-to-inference pipeline can be applied to a wide variety of geophysical survey methods, is agnostic to survey geometry and subsurface mesh resolution, and produces lightweight, lightning-fast AI models. We adopt a multitask approach to invert distributions of subsurface properties and simultaneously predict the location of anomalies in the subsurface. We find that, up to a negligible spatial tolerance, our models recover over 95% of anomalous volumes with more than 96% precision in our primary use case, which is the detection and classification of near-surface anomalies using magnetic data for the GOPHURRS project.

Coauthors: Piyoosh Jaysaval and Fred Day-Lewis (PNNL)

3:35 - 3:55 p.m.

Comparing Methods for Estimating Major Angles of Anisotropy in the Subsurface

Debbie Fagan, Pacific Northwest National Laboratory

Pacific Northwest National Laboratory is supporting the Nuclear Regulatory Commission (NRC) in review and development of geostatistical planning and analysis capabilities and implementation in Visual Sample Plan (VSP) software. VSP is a data quality objectives-based software tool for planning environmental sampling and conducting analysis of collected data (vsp.pnnl.gov). While VSP has historically provided two-dimensional (2D) isotropic geostatistical methods, three-dimensional (3D) anisotropic methods are under development for subsurface geostatistical data analysis.

Isotropy in environmental systems is the condition when a characteristic exhibits the same behavior in all directions. Anisotropy is the converse, where the characteristic follows a spatial pattern. An example is a subsurface contaminant plume, where the contaminant concentrations follow groundwater flow, rather than being uniformly distributed in the subsurface. The angles of anisotropy are required to adequately model contaminant concentration in the subsurface using geostatistical models.

Two algorithms, mass moment of inertia (MOI) and covariance tensor identity (CTI), were considered for the purpose of automatically determining the maximum angle of anisotropy as measured in subsurface geologic features. Both were evaluated by PNNL with respect to the accuracy of the resulting estimated angles of anisotropy, initially by applying them to simulated datasets and then using resampling techniques applied to the Hanford Site dataset in both a 2D-layered and 3D-volume approach.

One 3D test dataset comprised spectral gamma data from a selection of 70 groundwater wells which are in geographical proximity at the Hanford site.  A spectral gamma tool contains a high-purity germanium sensor that analyzes for natural radiation from the geologic formation. The patterns and ratios between the various spectral gamma analytes in 2D and 3D space can be used to interpret depositional history in the subsurface.

MOI outperformed CTI, though limitations of both methods were identified. Notably, the MOI-estimated angles of anisotropy within the Ringold Formation member of Wooded Island - unit E (located in the current flow of the Columbia River) are consistent with the paleo Columbia River channels inferred by Reidel (2013), located in the central region of the Hanford Site. This analysis aligns with Reidel 2013 conclusions and validates anisotropy estimation using MOI. The MOI method has been implemented in VSP for 2D and 3D data analysis and is available for others to use in the evaluation of anisotropy in the subsurface.

Coauthors: Moses Obiri (PNNL); Tollef Winslow (CPCCo); Swasti Saxena and Jen Huckett (PNNL)

3:55 - 4:15 p.m.

The Role of Geochemistry at the Aquitard-Aquifer Boundary and It's Impact on Public Supply Wells

Noah Heller, BESST, Inc.

Many public supply wells (PSWs) fail because their water chemistry does not meet regulatory standards, despite pilot hole water quality testing suggesting compliance. This is partly attributed to conventional testing that focuses on the mid-section of permeable zones, excluding low-permeability units or aquitards. The main goal is to prove yield, so groundwater is sampled within the tested interval for efficiency. Clay boundaries are typically excluded from zone testing because of low expected yields, but they may harbor elevated concentrations of constituents of concern. Well discharge concentrations may thus be non-compliant due to the blend of groundwater from permeable, high-yield zones and less permeable elevated concentration zones. We evaluated zonal flow and chemistry across the screens of 143 PSWs in California and Nevada, identifying the screen intervals with maximum arsenic, iron, manganese, and nitrate concentrations. We examined the relationship between sediment type, flow contribution, and maximum concentrations, focusing on the influence of aquitard boundaries and interbedded sequences on geochemical outcomes. Maximum concentrations occurred predominantly (73 to 84 %) in well screens associated with interbedded or coarse sediments with an aquitard boundary. Intervals with aquitard boundaries had higher arsenic concentrations (p = 0.05). In non-compliant wells, 64 to 69% of the maximum metal concentrations were sourced from fine-grained and interbedded sediments, warranting their inclusion in water quality zone testing. We recommend long-screened test wells to provide the geochemical resolution to determine the distance between aquitard boundaries and well screens and minimize the risk of constructing non-compliant PSWs that then require treatment.

Coauthor: Marina Feraud (BESST, Inc.)

4:15 - 4:35 p.m.

Implementing Improved Remediation and Performance Monitoring of Groundwater Contamination within Discrete High-Concentration Zones

Rebecka Iveson, Pacific Northwest National Laboratory

The 200-West Area Pump and Treat (P&T) Facility at the Hanford Site in southeastern, WA is designed to treat various contaminants of concern using a network of extraction wells, typically screened over large depth intervals to increase groundwater removal. The system is a crucial component of the remediation approach at Hanford to achieve site regulatory cleanup goals. Monitoring the performance of a P&T system with a network of relatively long-screened wells (up to 50 meters long) poses a challenge due to complex aquifer-well interactions that result in flow-weighted sampled concentrations, generally irrespective of pump depth intake. The resulting dilution may obscure the presence of high-concentration, low permeability zones within the aquifer, complicating remedy design and providing a false sense of completion. This work leverages targeted field characterization methods in four new extraction wells at Hanford to delineate vertical contaminant distribution, enabling more accurate predictions of P&T mass removal performance. Vertical flow measurements using a wireline electromagnetic flowmeter under ambient and pumped conditions were conducted. The measured inflow rates vs. depth are directly related to the vertical profile of hydraulic conductivity and hydraulic head outside the well screen; thus, relative hydraulic conductivity profiles were generated for each well. The detailed well characterization data informed the placement of depth-discrete, passive groundwater samplers to vertically delineate contamination in the aquifer. Preliminary results indicate geology-dominated flow patterns, notably lacking contributions from less permeable units regardless of pump intake depth. Results are anticipated to support the evaluation of depth-discrete remediation strategies (e.g., targeted well design, discrete-zone isolation, etc.) for enhanced site cleanup and P&T performance monitoring.

Coauthors: Rob Mackley and Fred Day-Lewis (PNNL); Darrell Newcomer and Tollef Winslow (CPCCo)