Nov. 8 Technical Session Recording Now Available

Introduction

beth parker

University of Guelph, Ontario, Canada

Using Temporary Deployed Sensors in Bedrock Boreholes to Improve Remediation Decisions & Monitoring at Complex Sites

Co-authors: Jonathan Munn, Carlos Maldaner, and Peeter Pehme, University of Guelph

Abstract

Characterization of contaminant distributions in fractured rock systems is both common and exceptionally challenging. In fractured rock systems, nearly all groundwater flow and downgradient contaminant transport occurs in the interconnected fracture network (secondary porosity), yet not all fractures are well-connected or equally transmissive. In sedimentary rocks, it is well-known that mass transfer between fractures and the lower permeability, porous rock matrix strongly affects contaminant plume behavior and remedial efficacy. In metamorphic and igneous bedrock (e.g. granite) the matrix porosity can be much lower, however still appreciable relative to fracture porosity, and in many cases enhanced by micro-fractures. A fundamental question in these systems is determining the number of hydraulically active fractures that influence average linear groundwater velocities and surface area for diffusion affecting plume front migration rates to assess risks and internal mass flux distributions needed to enhance remediation performance. Several new high-resolution field methods have been developed and tested for identifying hydraulically active fractures in bedrock boreholes where sensors can be temporarily deployed behind FLUTe liners (Keller et al. 2014). These liners allow re-creation of ambient flow system conditions, improved sensitivity active fracture identification and identification of aquitard occurrence from direct measurement of hydraulic head and flow. The updated DFN-M field approach provides an expanded toolkit for creating process-based CSMs and re-use boreholes for effective monitoring zone placement, optimizing site remediation costs. 

Theme: Environmental Remediation

Speaker #1

Andrew Binley

Lancaster Environment Centre, Lancaster University, Lancaster

Electrical Resistivity Imaging of Denitrifying Permeable Reactive Barriers

Co-authors: Lee Burbery and Theo Sarris, Institute of Environmental Science and Research, Christchurch, New Zealand; Richard Mellis and Mike Finnemore, Southern Geophysical Ltd., Christchurch, New Zealand; Giorgio Cassiani, Universita di Padova, Padova, Italy; Michael Tso, UK-CEH, Lancaster, UK

Abstract

Many parts of the world are experiencing increasing concentrations of nitrate in groundwater.  Woodchip denitrifying permeable reactive barriers (PRBs) enhance in situ natural nitrate attenuation in shallow groundwater systems. Solid carbon is added in trenches through the aquifer to intercept nitrate-contaminated groundwater flow. A critical element in the design of such PRBs is matching hydraulic conductivity of the PRB to the surrounding aquifer media to ensure that water flows through the PRB rather than around it.   In this case study we illustrate how electrical geophysics is being used to assess the performance of denitrifying PRBs installed in gravel aquifers of the Canterbury region, New Zealand.   A particular challenge of the setting is the very high advective velocity of local groundwater. We have used a series of solute tracer experiments coupled with time-lapse electrical resistivity imaging and solute transport modelling to characterise flow paths and residence times of groundwater in and around two trial PRBs. Electrical resistivity imaging has revealed surprisingly complex solute pathways within the PRBs, and highlight the potential degrading of hydraulic performance of the PRBs, which may limit their remediation effectiveness. 

 

Speaker #2

Adrián Flores-Orozco

Technical University of Vienna, Vienna, Austria

Monitoring the Injection of Nanoparticles for Groundwater Remediation by Means of Complex Conductivity

Co-authors: Jakob Gallistl, TU Wien, Vienna, Austria; Matthias Bücker, TU Braunschweig, Germany

Abstract

It has been demonstrated that subsurface amendment with nano- and micro-scale particles speeds up the degradation of pollutants and has the potential to reach areas not accessible with other methods. The high reactivity of the particles calls for the monitoring of subsurface changes in real time to evaluate the correct delivery of the particles into the target and the degradation of pollutants. This vital information cannot be gained through traditional borehole sampling. Here, we present complex conductivity (CC) results obtained along experiments conducted at the field scale (a) for data collected along the injection of Goethite nanoparticles (GNP) for the degradation of Toluene and (b) for data collected along the injection of micro-scale zero-valent iron (mZVI) particles to treat a plume of chlorinated aliphatic hydrocarbons (CAH). CC measurements were collected using electrodes placed on the surface and the measuring protocol was designed to collect a complete data set within 15 minutes.

For both presented experiments, initially high electrical conductivity values associated to the mature contaminant plumes decrease due to the injection of the solution containing the GNP and mZVI particles. Unexpectedly, large variations in the electrical images were resolved in the unsaturated zone and close to the surface (Fig. 1). The analysis of the affected sediments revealed the accumulation of particles due to an unexpected migration through fractures developed during injection, also confirmed by daylighting observed in wells up gradient from the injection point. Furthermore, the increase of the conductivity phase values indicates the degradation of the brush layer (coating mZVI) and interactions with the contaminants (see Fig. 1). Our results demonstrate that CC imaging permits to assess in real-time the path of the injected particles and their transformation. Accordingly, CC can be used to monitor in real-time changes in the subsurface due to particles injections and other in-situ remediation strategies.

Speaker #3

christopher power

Western University, Ontario, Canada

Numerical, Laboratory and Field Assessment of Electrical Resistivity Imaging of DNAPL Remediation

Co-authors: Jason Gerhard, Western University; Panagiotis Tsourlos, Aristotle University of Thessaloniki; 

Abstract

The remediation of sites contaminated with industrial chemicals – specifically dense non-aqueous phase liquids (DNAPLs) like coal tar and chlorinated solvents - remains a major geoenvironmental challenge. Remedial activities would benefit from a non-destructive technique to map the evolution of DNAPL mass in space and time. Electrical resistivity tomography (ERT) has long exhibited strong potential in this context but has yet to become a common tool at DNAPL sites. This presentation summarizes our numerical, laboratory and field studies that assesses the potential of time-lapse ERT for improved monitoring of DNAPL remediation. A new coupled DNAPL-ERT numerical model was developed and then employed to explore time-lapse ERT for monitoring a range of realistic DNAPL remediation scenarios at the field-scale. Laboratory tank experiments were also conducted to assess a new surface-to-horizontal borehole configuration for improved ERT mapping of DNAPL remediation. Finally, ERT was used to successfully monitor a DNAPL source zone undergoing thermal remediation at an industrial field site in New Jersey, USA. Overall, this body of work demonstrates that ERT is indeed promising for mapping DNAPL remediation, benefitting from recent advancements in this technique, including data acquisition, instrumentation and inversion.

Speaker #4

samuel falzone

Army Corps of Engineers/Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire

Early Evidence for Complex Resistivity as a Geophysical Field Method to Delineate PFAS Contamination

Co-authors: Ethan Siegenthaler, Kristina Keating, and Lee Slater, Rutgers University Newark; Charles Schaefer, CDM Smith; Dale Werkema, Environmental Protection Agency

Abstract

The distribution of polyfluoroalkyl substances (PFAS) in aqueous film forming foam (AFFF)-impacted source areas remains poorly understood, despite the growing urgency to deal with PFAS contamination. New field methods to delineate and characterize source zones are needed to better understand the fate of these contaminants in the subsurface, and to better assist with site management and future remediation efforts. While direct sampling and laboratory analysis for PFAS constituents are possible, these efforts result in sparse sampling of the affected area. Geophysics has the potential to provide a means to characterize AFFF-impacted source zones, within which PFAS contamination is more concentrated, on a more relevant spatial and temporal scale than direct sampling. The imaginary conductivity (’’) as measured with Complex Resistivity (CR) measurements is sensitive to changes in surface charge associated with cation sorption. As PFAS is known to closely associate with the pore surface, CR seems a likely choice to study environmental PFAS contamination. To assist with the ongoing effort to better address PFAS contamination, we explore the potential for CR to characterize PFAS contaminated source zones through a series of bench-scale experiments and field surveys.

In bench-top studies we have observed promising trends in synthetic and legacy contaminated soils indicating that ’’ is sensitive to the presence of PFAS contamination. We have also observed trends in soils treated to remove PFAS that further indicates sensitivity of ’’ to PFAS concentrations. In addition to laboratory data, we present early field evidence that CR surveys can delineate variations in PFAS concentrations associated with a legacy source zone of contamination.


 

Speaker #5

hilary p. emerson

Pacific Northwest National Laboratory (PNNL), Richland, Washington

Spectral Induced Polarization for Monitoring In Situ Remediation at Department of Energy's Hanford Site

Co-authors: James E. Szecsody, Amanda Lawter, Eleda Fernald, Adam Mangel, Judy Robinson, Nikolla Qafoku, and Vicky Freedman, PNNL, Richland, Washington; Christopher Halter, Eastern Washington University, Cheney, Washington 

Abstract

Groundwater sampling and sediment coring have been reliably used to infer biogeochemical reactions occurring in situ during active and passive remediation. While these techniques are informative, there are disadvantages including (1) the challenge of selecting representative locations for point sampling and (2) high costs associated with monitoring well installation and sampling. Noninvasive geophysical tools can monitor large volumes of the subsurface with relatively high spatial resolution to infer solution and surface biogeochemical changes over time. Along with traditional sampling, geophysical methods can be used (1) during active remediation as indirect indicators of contaminant transformations and (2) as part of an overall strategy for long-term monitoring of subsurface contaminated sites. 
 
Spectral induced polarization (SIP) is a geophysical technique that is sensitive to solution properties (e.g., ionic strength) and surface reactions (e.g., adsorption, precipitation) that modify surface properties (e.g., surface area, grain size, polarizability). Laboratory column experiments were conducted to collect SIP data for different remediation amendments applicable to ongoing cleanup efforts at the Hanford Site (Washington, USA), including zero valent iron (ZVI), sulfur-modified zero valent iron (SMI), calcite, and apatite. Experiments were conducted in saturated columns with concurrent monitoring of major geochemical parameters (e.g., solution conductivity, pH, oxidation-reduction potential, and dissolved oxygen) to identify the (1) sensitivity for detection of individual amendments in static (no-flow) conditions, (2) detectability of amendments during in situ injection and precipitation, and (3) change in SIP signal over time to quantify change in amendment reactivity. The greatest sensitivity was observed for conductive materials, including ZVI and SMI, with detection limits as low as 0.2 wt.% based on phase shifts and imaginary conductivity measured via SIP. Shifts in phase and imaginary conductivity peaks measured by SIP were also observed due to changes in amendments over time suggesting changes in reactivity. Apatite and calcite had a greater response at higher concentrations which may be due to physical changes in porosity from precipitation rather than the mineral phase. These results demonstrate a first step for validating SIP as a method for field-scale monitoring remediation activities at Hanford and other sites.

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Theme: Environmental Site Characterization and Monitoring

Speaker #1

roelof versteeg

Subsurface Insights, Hanover, New Hampshire

Integration of Measurements, Modeling and Parameter Estimation for a Predictive Site Understanding

Co-authors: Rebecca Rubinstein, Ali Meyal, Haiyan Zhou, Subsurface Insights; Reza Soltanian, University of Cincinnati; Aaron Peacock, Microbac

Abstract

Effective site remediation requires auditable and transparent integration of analytical tools with multi scale and multi domain measurements and models. This integration should be centered around reactive transport models which can predict fate and transport of contaminants.

One major challenge is that while reactive transport models can directly accommodate and use several datasets (such as hydrological head data or concentration data), it has been challenging to use other data or models.

For instance, timelapse electrical resistivity data has been shown to be extremely informative for contaminant behavior, but is not something which can be easily integrated in reactive transport models. Similarly, microbiological data contains large amounts of information about key processes, but is not something which is readily integrated in reactive transport data.

We will present progress results on a powerful integrated framework (Predictive Assimilation Framework) which provides comprehensive data management, analytics and modeling capabilities which jointly provide actionable understanding of system behavior.

We will discuss two components. The first one – Omics to Reactive Transport (ORT – Figure 1) provides a streamlined workflow to couple microbe-scale and macroscale processes using the outputs of KBASE and PFLOTRAN. It does this in an iterative manner, allowing there to be a process level coupling which avoids a lot of the standard scaling challenges.

The second component is novel autonomous electrical geophysical monitoring hardware which is integrated with a data management, processing and parameter estimation pipeline which couples E4D, PEST and PFLOTRAN in a data domain approach to effectively utilize timelapse electrical geophysical data in the optimization of reactive transport models (Figure 2).

Speaker #2

hang chen

Boise State University, Boise, Idaho

Improving Subsurface Characterization with Sequential Inversion of Multiple Geophysical Datasets

Co-authors: Qifei Niu, Boise State University

Abstract

Subsurface heterogeneity impedes our understanding of the hydrological conditions of contaminated sites. In the last several decades, geophysical methods have been frequently used in characterizing the contaminated subsurface due to cost-effectiveness and invasive nature of the technique. Since the hydrological conditions of many sites are very complex, traditional geophysical tests with a single imaging method may not fully resolve the heterogeneity needed in subsurface remediation modeling for predictive understanding. In particular, smoothness constraint imposed by regularization, which is necessary to make the optimal solution unique, may induce significant biases to the estimated hydrological properties even if the hydrogeophysical models are known and related model parameters are accurate.

In this study, we propose a sequential inversion method for subsurface characterization with seismic travel-time data and electrical resistivity data. The seismic travel-time data are first inverted to generate the spatial distribution of the seismic velocity, which is then used to determine the structural characteristics of the subsurface. The subsurface is then divided into zones featuring different structural properties, and these zones are then used to guide the inversion of resistivity data. In the guided resistivity inversion, the regularization (i.e., smoothness constraints) across the boundary between two zones are relaxed to preserve the discontinuity. Two synthetic models and two field cases are used to demonstrate the use of the proposed inversion. Archie’s law is used to translate the inverted resistivity into water content in a stochastic way such that the uncertainty induced by inaccurate model parameters can also be quantified. The results show that the proposed inversion strategy can help reduce the biases induced by the smooth constraint of the regularization and thus can be applied for subsurface hydrological characterization.

Speaker #3

judy l. robinson

Pacific Northwest National Laboratory (PNNL), Richland, Washington

Electrical Mapping of Paleochannels Demonstrating the Value of Non-invasive Imaging at the Hanford Site

Co-authors: J. Thomle, D. McFarland, K. Deters, M. Rockhold, F. Day-Lewis, V. Freedman, PNNL, Richland, Washington

Abstract

Characterization of aquifer structure (e.g., geologic contacts, structures, and lithology) remains a major challenge in hydrogeology despite decades of research in subsurface imaging and hydrologic parameter estimation. A critical component of aquifer structure is transmissive stratigraphic features, or paleochannels, which create preferential hydraulic connections and allow downgradient migration of groundwater contamination. Incorporating the location(s) of these features in a geologic framework model (GFM) directly supports conceptual and reactive transport model development which is necessary for focused and effective remedial action. At the Hanford Site in WA, USA, paleochannels are buried ancestral fluvial channels associated with the Columbia River and cataclysmic Ice Age floods. The approximate location of these stratigraphic features has been inferred through interpolation of physical and chemical borehole data including geophysical logs, grain-size analyses and contaminant concentrations. Where there is sparse borehole coverage or incomplete data from wells, the interpolation between locations is uncertain. Non-invasive geophysical imaging can play an important role in filling gaps between boreholes and reducing characterization costs.

We present a case study using large scale electrical mapping to identify hydrostratigraphy and potential paleochannels at the Hanford Site. In two field campaigns, over 36 line-kilometers (km) of electrical resistivity tomography (ERT) data were collected along 14 transects. ERT is highly effective at the Hanford Site because lithologic contrasts have associated contrasts in electrical conductivity. ERT surveys were sited and performed to image critical aspects (e.g., paleochannels, stratigraphic contacts) of the subsurface. Inconsistencies between the GFM and ERT were catalogued to provide a basis for future site characterization using complementary geophysical methods and (or) direct sampling. A general workflow will be presented for using ERT to confirm, refine, or reject aspects of a GFM.

Speaker #4

Xiaoqin Zang

Pacific Northwest National Laboratory (PNNL), Richland, Washington

Acoustic Communication Along Drill Strings for Deep Subsurface Monitoring 

Co-authors:  Jayson J Martinez, Aljon Salalila, Orlando A Garayburu Caruso, Christopher E Strickland, Z. Daniel Deng, PNNL; Yang Yang, Chinese Academy of Science

Abstract

Subsurface monitoring at a carbon storage site is important for tracking the movement of CO2 and the status of the site for geologic storage. Therefore, advanced monitoring technologies and effective methods to transmit data from downhole to the surface are needed to reduce the cost and uncertainty in measurements and satisfy regulations for tracking the fate of subsurface CO2. This study covers the design, development, and initial laboratory-scale feasibility study of an acoustic communication system for monitoring the deep subsurface. We set up a metal tubing in a lab space as the model and designed a hardware system for acoustic signal transmission and data collection. Tri-axis accelerometers were installed at eleven locations on the testing tube to receive the encoded-signals transmitted from a PZT transducer. The signal attenuation along the string and the impulse response of the acoustic channel were investigated. Using an inverse filter processing method, communication signals were successfully recovered and decoded with zero bit errors at all testing locations when the signal-to-noise ratio is 0 dB.