Dense non-aqueous phase liquid (DNAPL) contamination of fractured rock remains a long-term, persistent Department of Defense (DoD) problem. The diffusion of aqueous phase contaminants into low-permeability matrix blocks between fractures, or in and from dead-end fractures, limits the efficiency of fractured-aquifer remediation methods. Characterizing the physical properties of the rock containing the contaminant mass around fractures is critical for improving remediation operations in fractured rock settings. The primary objectives of this research were to

1. determine the sensitivity of two emerging borehole geophysical technologies (nuclear magnetic resonance [NMR] and complex resistivity [CR]) to key pore geometric properties (primarily pore size distribution and permeability) controlling contaminant transport,
2. investigate the potential sensitivity of emerging geophysical methods to contaminant mass (as DNAPL and/or aqueous phase) isolated within the immobile porosity of fractured rock inaccessible to aqueous sampling techniques, and
3. evaluate the predictive capabilities of these geophysical technologies with respect to quantifying immobile porosity and/or contaminant mass concentration.

A final objective was to investigate whether a mass transfer coefficient and the ratio of mobile to immobile porosity could be estimated for rock matrix from an electrical tracer test.

The technical approach involved [1] fine-scale delineation of contaminant mass around fractures using a discrete fractured network (DFN) approach, [2] fine-scale delineation of porosity, permeability and pore size distribution from core samples acquired as part of the DFN, [3] laboratory and borehole NMR and CR logging, and [4] laboratory tracer experiments coupled to pore-scale modeling to quantitatively link geophysical responses to contaminant mass transfer parameters. Laboratory measurements on cores and borehole logging data were acquired at three sites of DoD relevance: [1] the Naval Air Warfare Center (NAWC), West Trenton, NJ, [2] Santa Susana Field Laboratory (SSFL) in Southern California, and [3] Hydrite Chemical Company (HCC) in Wisconsin. This permitted assessment of geophysical technology performance within a range of sedimentary rock geological settings.

A number of key findings regarding the role of the NMR and CR technologies in support of remediation of contaminated sites resulted from this project. The exhaustive laboratory analysis of 75 cores from the three sites demonstrated that quantitative assessment of immobile versus mobile porosity and permeability is possible using both NMR and CR. NMR logging highlighted the potential to extract information on variations in these pore geometric properties in situ along a borehole, albeit with lower resolution. CR measurements from an existing commercially available borehole logging tool did not have the sensitivity to reliably detect these variations in pore geometry in situ. Statistical analysis of the NMR and CR logging signatures against contaminant mass distributions recorded in six boreholes from the three sites did not show a conclusive dependence of NMR or CR parameters on contaminant mass. However, preliminary laboratory tracer tests coupled to pore network modeling indicated the potential to quantitatively predict contaminant mass transfer parameters (rate coefficients and immobile to mobile porosity ratio) from simultaneous measurements of CR and fluid electrical conductivity.

The unique, extensive database of core-scale and field scale physical, hydrogeological and aqueous geochemical data acquired on this project provided new information in support of recent conceptual models for the distribution of contaminant mass around hydraulically active fracture zones. Technology transfer efforts focused on disseminating key aspects of the work through novel spreadsheet tools and online videos generated by the project team. The geophysical technologies investigated here could ultimately be applied to assess the effectiveness of multiple existing remedial technologies (e.g. bioremediation, thermal treatment, monitored natural attenuation (MNA), chemical addition) in reducing contaminant mass in the rock matrix, particularly adjacent to hydraulically active fractures. (Project Completion - 2020)

Briggs, M. A., F.D. Day‐Lewis, J.B. Ong, J.W. Harvey, and J.W. Lane. 2014. Dual‐domain Mass‐transfer Parameters from Electrical Hysteresis: Theory and Analytical Approach Applied to Laboratory, Synthetic Streambed, and Groundwater Experiments. Water Resources Research, 50:8281– 8299. https://doi.org/10.1002/2014WR015880.

Day-Lewis, F.D., L.D. Slater, J. Robinson, C.D. Johnson, N. Terry, and D. Werkema. 2017. An Overview of Geophysical Technologies Appropriate for Characterization and Monitoring at Fractured-rock Sites. Journal of Environmental Management, 204:709-720.

Day-Lewis, F.D., K. Singha, M.A. Briggs, N. Linde, and R. Haggerty. 2017. Geoelectrical Monitoring of Solute Transport in Dual-Domain Media: A Review. GSA Annual Meeting in Seattle, Washington, Paper No. 326-6. https://gsa.confex.com/gsa/2017AM/webprogram/Paper303924.html.

Day-Lewis, F.D. 2018. Pore Network Modeling of the Complex Conductivity Signature of Dual-Domain Mass Transfer. American Geophysical Union Fall Meeting, Abstract #H11I-1574. http://adsabs.harvard.edu/abs/2018AGUFM.H11I1574D.

Day-Lewis, F.D. 2019. Advances in Geoelectrical Monitoring of Solute Transport in Dual-Domain Media. European Union General Assembly, Geophysical Research Abstracts, 21:EGU2019-11955. https://meetingorganizer.copernicus.org/EGU2019/EGU2019-11955.pdf.

Falzone, S., K. Keating, B.L. Parker, F.D. Day-Lewis, J. Robinson, and L.D. Slater. 2018. Exploring the Relationship Between Sorption, Mass Transfer, and Flow Rate in Dual Domain Porosity Media. AGU Fall Meeting, Abstract #H41J-2202. http://adsabs.harvard.edu/abs/2018AGUFM.H41J2202F.

Falzone, S., L.D. Slater, F.D. Day-Lewis, B.L. Parker, K. Keating, and J. Robinson. 2017. Characterizing Mobile/Less-Mobile Porosity and Solute Exchange in Dual-Domain Media Using Tracer Experiments and Electrical Measurements in a Hassler-Type Core Holder. AGU Fall Meeting, Abstract #H21P-08. https://ui.adsabs.harvard.edu/abs/2017AGUFM.H21P..08F/abstract.

Robinson, J., L.D. Slater, K. Keating, B.L. Parker, F.D. Day-Lewis, and T. Robinson. 2016. Permeability Prediction of High Spor Samples from Spectral Induced Polarization (SIP): Limitations of Existing Models. AGU Fall Meeting, Abstracts # H43L-04. http://adsabs.harvard.edu/abs/2016AGUFM.H43L..04R.

Robinson, J., L.D. Slater, K. Keating, B.L. Parker, and T. Robinson. 2017. Relationship Between Pore Geometric Characteristics and SIP/NMR Parameters Observed for Mudstones. AGU Fall Meeting, Abstract #H21A-1430. http://adsabs.harvard.edu/abs/2017AGUFM.H21A1430R.

Robinson, J., L.D. Slater, K. Keating, B.L. Parker, C. Rose, J.R. Meyer, C.D. Johnson, T. Robinson, P. Pehme, S. Chapman, and F.D. Day-Lewis. 2015. Evaluating Petrophysical Relationships in Fractured Rock using Geophysical Measurements. AGU Fall Meeting, Abstract #H14A-07. http://adsabs.harvard.edu/abs/2015AGUFM.H14A..07R.

Robinson, J., L.D. Slater, A. Weller, K. Keating, T. Robinson, C. Rose, and B. Parker. 2018. On Permeability Prediction from Complex Conductivity Measurements Using Polarization Magnitude and Relaxation Time. Water Resources Research, 54:3436– 3452.

Robinson, T., K. Keating, J. Robinson, L.D. Slater, and B.L. Parker. 2016. Magnetic Susceptibility: Correlations with Clay Content and Apparent Diffusion Coefficients Controlling Electrical Double Layer Polarization. AGU Fall Meeting, Abstract #ED31B-0876. http://adsabs.harvard.edu/abs/2016AGUFMED31B0876R.

Robinson, J., L.D. Slater, K. Keating, T. Robinson, B. Parker, C. Rose, and M. Prasad. 2018. On Permeability Estimation for Mudstones using Geophysical Length Scales. Society of Exploration Geophysicists, SEG Technical Program Expanded Abstracts, 4889-4893.

Slater, L., F. Day-Lewis, S. Falzone, K. Keating, D. Ntarlagiannis, and B. Parker. 2019. March. Complex Resistivity (CR) Monitoring of Tracer Tests for Assessing Mass Transfer and Sorption in Low Permeability Media. SAGEEP 2019-32nd Annual Symposium on the Application of Geophysics to Engineering and Environmental Problems, Abstract. http://www.earthdoc.org/publication/publicationdetails/?publication=95817.