NGWA Conference on Fractured Rock and Groundwater: Alphabetical Content Listing
Daniel J. Goode
John N. Dougherty, PG
Characterizing Vertical Fracture Connections using Pressure Responses due to the Short-circuiting of Injection Water during Constant Head Tests
Field Measurement of Sorption Coefficients and Rates of Diffusion, Biodegradation, and Abiotic Degradation in the Rock Matrix
Thomas E. Imbrigiotta
Low-transmissivity rock strata at contaminated fractured rock sites frequently remain the predominant long-term source of chlorinated volatile organic compounds (VOCs) to the high-transmissivity fractures even after years of engineered or natural remediation. The US Geological Survey and the University at Buffalo, in cooperation with the US Navy and the Strategic Environmental Research Development Program, are developing and testing a downhole packer tool to estimate sorption coefficients and diffusion, biodegradation, and abiotic degradation rates of chlorinated VOCs in these low-transmissivity rock strata. The tool is used to isolate a 2-foot-long section of the open interval of a borehole that does not contain high-transmissivity fractures. A closed-loop system is used to conduct tracer tests by first stripping VOCs from the native water and then re-injecting this water, along with organic and inorganic tracers, back into the test section. The closed-loop system is used to periodically collect low-volume water samples to monitor for the reappearance of VOCs, the disappearance of tracers, and the appearance of degradation products.
Several in situ experiments were conducted in boreholes in different low-transmissivity rock strata with different levels of contamination by trichloroethene (TCE) and cis-1,2-dichloroethene (cisDCE). In general the results showed increases in TCE and cisDCE concentrations in the test section with time that were used to estimate bulk diffusion rates and sorption coefficients. Concentrations of bromide, the inorganic tracer diffusing into the rock matrix from the test section, decreased slowly with time and were used to estimate the rock matrix diffusion rate not affected by sorption, biodegradation, or abiotic degradation. The rate of production of degradation products of TCE and trichlorofluoroethene (the organic tracer not present at the site and a TCE analog) provided estimates of the biodegradation rates. Inverse solute transport modeling was used to estimate the best-fit sorption coefficients, diffusion parameters, and degradation rates.
Forced-Gradient Tracer Tests in a Fractured Limestone Aquifer Designed and Interpreted by 3D Numerical Modeling
The pumping test and the geologic investigations showed that the limestone aquifer was highly permeable, with fracture flow dominating the hydraulic response. Most tracer tests resulted in a very fast tracer arrival, indicating a very good connectivity between wells at a similar depth as the pumping well. Strong diffusive interaction between fractures and matrix was revealed by significant tailing in the tracer breakthrough curves. In one tracer test, tracers were injected before starting to pump to allow the tracers to diffuse more into the matrix. This resulted in lower breakthrough concentrations and longer tailing, representing mainly the back-diffusion from the matrix. Deeper wells and crushed upper layers have less connectivity to the pumping well and show slower tracer breakthroughs.
The breakthrough curves from the tracer tests were used to test different model concepts. A discrete-fracture model could be fitted best to the observed breakthrough curves. It demonstrated the importance of including fracture flow and transport in the modeling of fractured limestone sites. The calibrated model was used to analyze the spreading behavior of the contaminant plume.
Issam Bou Jaoude
In Situ Characterization of Processes Controlling Long-Term Release of CVOCs from Low-Permeability Zones
Daniel J. Goode
Investigation of Hydrogeologic Impacts at Two Historic Landfills Overlying Fractured Bedrock in the Lower Hudson Valley, NY
William, A. Canavan, PG
J. Michael Hawthorne, PG
Weathering, Structural Style and Frequency in Fractured Bedrock Contaminant Source Areas at Two Sites in the UK
Kevin Leahy, Ph.D.
Ryan Wymore, PE
Monitoring the Distribution of a Groundwater Remediation Reagent in Fractured Bedrock with Water Quality Sondes
Adam Hobson, PG
Quantifying Mobilization of Chlorinated Ethene Compounds Following Bioaugmentation in a Fractured Mudstone
Allen Shapiro, Ph.D.
This investigation demonstrates that integrating site characterization with groundwater modeling and the strategic location of monitoring boreholes can be used to evaluate the effectiveness of remediation conducted in fractured rock. Bioaugmentation of chlorinated ethene (CE) compounds was conducted in the mudstone underlying the former Naval Air Warfare Center, West Trenton, NJ. Groundwater modeling was used to design locations for monitoring, and the location and injection volume of bioaugmentation amendments. Groundwater fluxes from the model were coupled with CE concentrations from monitoring boreholes to formulate a CE mass balance of the region targeted in the bioaugmentation. Differences in CE fluxes into and out of the rock volume identified the total CE mobilized from diffusion, desorption, and NAPL dissolution under pre- and post-injection conditions. The mobilized CE mass was compared with the initial CE mass in the rock matrix estimated from analyses of rock core conducted prior to the bioaugmentation.
The CE mass mobilized per year prior to the bioaugmentation was small relative to the total CE mass in the rock matrix, indicating that hundreds of years would be needed for current pumping and natural attenuation to achieve remedial objectives. The post-injection CE mobilization rate increased by an order of magnitude, but multiple remediation applications would be needed over decades to reduce CE concentrations to acceptable limits.
Ryan Wymore, PE
Kevin Kelly, PG
The mile-long commingled VOC plume in bedrock extends through a densely populated area located in the Newark Basin of northern New Jersey where residential wells are still in use. The primary reason bioaugmentation was chosen was the lack of naturally-occurring bacteria in the bedrock aquifer, unlike the overburden aquifer. The goals of bioaugmentation were to reduce the time and cost associated with bioremediating the residual mass, to mitigate contaminant mass-flux and to demonstrate the effectiveness of bioaugmentation as a potential remedy scalable to larger areas.
The design basis was a high-resolution mapping of the fracture network, which includes bedding plane partings as well as tectonic fractures. Using hydraulic conductivity data from discrete fracture zones gathered in part from tracer studies, over 8,500 gallons of customized EVO products, with suitable droplet sizes tailored to specific fracture zones, were injected in November 2015. The EVO was augmented with SDC-9, a DHC-containing bacterial culture. We evaluated the results of six performance monitoring events in 2016 and 2017. Chlorinated methane remediation (CTC and chloroform) was particularly robust. The use of custom droplet sizes to address the variable groundwater velocities (<1 to >10 fpd) and vertical extent (>200 feet deep) will be reviewed. Challenges and solutions that will be discussed include transient decreases in pH to very low (toxic) levels, excessive iron production, complex geochemistry, biofilm and biocrust formation, and unpredicted distribution of amendments.
Geochemical and Microbiological Progress Metrics for Bioremediation of Mixed Chlorinated Ethenes & Methanes
To address the impacted bedrock aquifer that lacked naturally-occurring bacteria (no DHC), approximately 8,500 gallons of emulsified vegetable oil (EVO) augmented with SDC-9, a DHC-containing bacterial culture, was injected into a complex fracture network comprised of bedding plane and tectonic fractures. The goal of the advanced monitoring was to support the demonstration of the effectiveness of bioaugmentation as a potential remedy scalable to larger areas, but also to characterize the reasons for challenges that presented themselves and to optimize the design.
Bioaugmentation performance was evaluated and quantified using a 3D monitoring well network with analyses for both chemical and biological constituents. The parameters monitored included concentration trends of tracers, of chlorinated ethenes, ethanes, methanes and benzenes (including all daughter products), geochemical conditions (DO, ORP, pH, alkalinity, methane, ethane, ethene, sulfate, ferric and ferrous iron, manganese, TOC), biological conditions (Dehalococcoides (DHC) functional genes bvcA Reductase (BVC) and vcrA Reductase (VCR), functional gene tceA Reductase and dehalobacter (DHBt), and metabolic products of the organic substrate), and stable isotope changes (CSIA) in chlorinated ethene parent and daughter compounds. Seasonal influences were also recognized and given consideration in our evaluation. The results of our monitoring of progress metrics showed that enhanced biodegradation of chlorinated VOCs was successful in particular portions of the fracture network that were treated by injected amendments.
Treatment injections were performed using another unique short-interval straddle packer. This allowed for the surgical placement of the proper volume and density of the treatment slurry to match the contaminant concentration at a given depth. Injections were performed using a highly versatile injection unit capable of injection rates between 8 and 300 gpm and injection pressures of up to 2,000 psi. The injection rates and pressures were tailored to the formation lithology to achieve maximum distribution and delivery of the treatment.
The five sites that were closed achieved non-detect levels of the contaminants of concern. The equipment referenced above will be presented and described in detail.
Kenneth J. Goldstein
Comparing Rock Matrix Contaminant Profiles Downgradient of a DNAPL Source after 10 Years of Groundwater Dissolution
Jessica Meyer, Ph.D.
Conceptualization of Contamination Using Depth Discrete Monitoring of Dynamic PCE Conc. Changes During Pumping
Mette M. Broholm
The highest PCE concentrations were observed in the upper crushed Copenhagen limestone and the highly fractured Copenhagen limestone, with lower and decreasing concentrations with depth in the underlying Bryozoan limestone. Significant concentration increases were observed when remedial pumping and re-infiltration was discontinued (in one case from < 1 to > 250 µg/L PCE). The concentration changes in the near source area were very dynamic in the fractured Copenhagen limestone. The dynamic changes observed are most likely due to fast fracture flow and back-diffusion from the limestone matrix in areas with residual contamination. The crushed limestone responded more slowly compared to the fractured zone and pumping in the fractured limestone had limited impact on the crushed zone concentrations. In addition to visualization and interpretation of the PCE distribution, the 3D model was used to deduce the likely zones of origin for the observed PCE contamination, showing that the P&T system has little effect on the contamination in parts of these zones. The new conceptual understanding can be used to optimize the remediation.
To better understand the character of natural fracture networks at an active quarry research site located in a structurally complex setting the authors collected a dataset comprised of fracture plane orientations, fracture intensity variations, geologic framework, and lithofacies. The application of unmanned aerial vehicles (UAVs), LIDAR (Light Detection and Ranging) and photogrammetry allowed for collection of a high fidelity, high confidence geotechnical dataset. The purpose of this research was to use an outcrop derived dataset to propagate fracture networks into the subsurface and analyze potential zones of high permeability contributing to water discharges. Multiple fracture sets were identified. Listric faults associated with negative flower structures show increased fracture intensity near the fault zones. Fracture sets remain consistent throughout the interbedded chalks, marls, and limestones. However, there is an apparent variability of fracture spacing associated with changes in lithology. In order to better analyze fracture patterns and fracture drivers a 3D geological model consisting of structural framework, lithofacies model, and discrete fracture network (DFN) was developed. The incorporation of high resolution data into subsurface reservoir models improved the mapping capability for fluid migration pathways. The resulting reservoir model contributed to a better understanding of surface water and groundwater interactions allowing for improved water resource management, source water protection, and mine planning.
Robert M. Bond, P.G.
The high resolution study area is at the head of a 5,000-foot commingled VOC plume in bedrock, located in the Newark Basin of northern New Jersey, which ultimately discharges to surface water. The design basis for the bioremediation injections was a high-resolution mapping of the fracture network, which includes shallow-dipping bedding plane partings as well as steeply-dipping tectonic fractures, and the intersections of both. Detailed 3D hydraulic conductivity data was collected from discrete fracture zones in part from multiple fluorescent tracer studies. This evaluation was important to customizing the emulsified vegetable oil (EVO) product into suitable droplet sizes tailored to specific fracture zones. We used custom droplet sizes to address the variable groundwater velocities (<1 to >10 fpd) and vertical extent (>200 feet deep) in the residual source area fracture network.
After injection of over 32,000 liters of EVO we further evaluated the fracture network by visualizing hydraulic responses as well as changes in performance monitoring parameters in six successive sampling and analysis episodes. With a more comprehensive understanding of the fracture network and contaminant concentrations within the open fractures and the rock matrix, there is a higher probability of implementing a successful remedial injection design.
Overview of FACT Method for a Continuous Profile of Dissolved Phase Contaminant Distribution in Fractured Rock
A very wide range of regular, irregular and random fracture shapes is considered, in monodisperse or polydisperse networks containing fractures with different shapes and/or sizes. A simple and new model involving a dimensionless density and a new shape factor is proposed for the percolation threshold rho_c, which accounts very efficiently for the influence of the fracture shape. It applies with very good accuracy to monodisperse or moderately polydisperse networks, and provides a good first estimation in other situations. A polydispersity index is shown to control the need for a correction, and the corrective term is modelled for the investigated size distributions.
Moreover, and this is practically crucial, the relevant quantities in rho_c can all be determined from trace maps. An exact and complete set of relations can be derived when the fractures are assumed to be Identical, Isotropically Oriented and Uniformly Distributed (I2OUD). Therefore, the dimensionless density of such networks can be derived directly from the trace maps and its percolating character can be a priori predicted.
Since these relations involve the first five moments of the trace lengths, truncation effect due to the boundaries of the sampling domain can be important. However, it can be shown that this effect can be exactly corrected, for any fracture shape, size and orientation distributions, if the fractures are UD.
Systematic applications are made to real fracture networks and to numerically simulated networks. Possible extension to networks which are not I2OUD are examined.
Quantifying Matrix Diffusion and Redox Effects on Hexavalent Chromium Plume Conditions in a Fractured Mudstone
Beth L. Parker, Ph.D.
Ryan Wymore, PE
Kent Novakowski, Ph.D, PG
Matthew Becker, Ph.D.
The technology was demonstrated in a well-characterized crystalline bedrock. Fiber optic cable was coupled borehole walls using an over-pressured flexible liner outfitted with an air coupled transducer to measure fluid pressure. DAS was used to measure strain every 0.25 m along the fiber optic cable in the monitoring wells. At one well, strain and pressure were measured simultaneously at a known fracture zone that is hydraulically connected to the pumping/injection well 30 m away. Strain amplitudes less than one nm/m were measured in response to head amplitudes of less than two mm. Clean strain signals were detected at tested periods of hydraulic oscillation ranging from 2 to 18 minutes. The response was sensitive to the fiber optic cable design with tight-buffered fiber optic cable being about twice as sensitive to strain as standard gel-filled fiber in metal tube. This first field test suggests potential for measuring hydraulic connectivity and hydromechanical behavior in fractured formations through cementing fiber optic cable in wellbores outside of well casings.
Geophysical Methods for Karst Feature Identification at Underground Storage Tank Facilities in Kentucky
William Alley, Ph.D.
Kent Novakowski, Ph.D, PG
Todd G. Umstot
Ryan Wymore, PE
The ITRC fractured rock guidance is not intended to be a comprehensive “cook book” for characterization and remediation of fractured rock sites, but rather its focus is the primary differences compared to unconsolidated sites. The document begins with a discussion of various geologic terranes, with an emphasis on how this can affect fracture types present at a site. Following the geology discussion, the document presents the fundamentals of groundwater flow and contaminant transport in the rock matrix and in fractures, as well as the role of back diffusion in both sedimentary and igneous/metamorphic rocks. As with past ITRC documents, the fractured rock guidance presents an integrated and iterative process for site characterization and updating the conceptual site model, including a new and improved tools selection matrix. The document presents a primer on how to evaluate, select, implement, and monitor remediation technologies at fractured rock sites, and includes an introduction to modeling, highlighting the significant limitations to modeling in bedrock. Finally, the guidance covers regulatory concerns and stakeholder issues as well as presenting numerous case studies.