NGWA Conference on Fractured Rock and Groundwater: Alphabetical Content Listing

Characterizing Flow and Contaminant Transport Properties

Daniel J. Goode

Assessing Monitored Natural Attenuation as a Remedy in Igneous Fractured Rock

John N. Dougherty, PG
Estimates of groundwater flow velocity, abiotic test results, and bedrock property data were used in the CRAFLUSH model to assess the natural attenuation of contaminants in groundwater in the crystalline fractured rock. The model results showed that natural attenuation can account for the significant decrease in the concentration of volatile organic compounds observed in groundwater between two transects of monitoring wells installed at the site. The two transects of wells were installed to estimate mass flux/mass discharge under ambient conditions in support of evaluation of groundwater remedies for the bedrock aquifer including monitored natural attenuation. Groundwater flow velocity was estimated using aquifer properties derived from borehole dilution tests, passive flux meters, test pumping, and potentiometric surface data. A bench scale test was conducted to assess the potential for abiotic degradation of trichloroethene in the bedrock aquifer Previously, bedrock at the site has been characterized using rock core, CORE DFN sampling to assess matrix diffusion, FLUTe liner transmissivity profile, Active Line Source (ALS) temperature logging, packer testing, borehole geophysical logging, heat pulse flowmeter logging, compound specific isotopic analysis, and wireline groundwater sampling.

Characterizing Vertical Fracture Connections using Pressure Responses due to the Short-circuiting of Injection Water during Constant Head Tests

Natasha Augustine
A discrete fracture approach is often required for modeling groundwater flow in complex bedrock aquifers at the local scale. This approach, however, depends on a number of parameters (i.e. fracture density, connectivity, and orientation) not easily obtained from traditional hydraulic testing techniques. Additionally, the hydraulic properties estimated from typical field methods generally reflect near borehole conditions, which may or may not be representative of dominant flow pathways in the larger aquifer system. A study is presented which illustrates how measuring head changes above and below the isolated interval during constant head tests can yield value-added information to address these limitations. A total of 25 tests were completed in two 152 mm diameter boreholes drilled to approximately 40 m depth in a granite gneiss aquifer. A constant-head testing system with packer spacing approximately two-m in length was used with separate pressure measurements recorded in the open hole interval above the system, in the test section, and in the shut-in section below. Significant pressure increases were observed in a number of shut-in intervals where the test section intersects low-moderate transmissivity zones. Responses with reduced magnitude also occurred in the upper open hole interval above the test section. It is hypothesized that: (1) Pressure increases occur when injection water short-circuits through adjacent vertical fractures into the observation intervals above and below the test zone; (2) Lower magnitude responses in the upper open hole section are due to wellbore storage; and (3) A lack of increased pressures outside the test zone may indicate no vertical connections exist. Numerical modeling of test results provide additional insights regarding the transmissivity and geometry of possible vertical connections. As the additional measurements collected during this study involved minimal extra cost and labour they represent a significant opportunity to augment information already collected with standard constant head testing techniques.

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

Klaus Mosthaf
The importance of fracture flow and transport in a fractured limestone was investigated with a hydraulic pumping test combined with six tracer tests. The pumping test was conducted in a PCE-contaminated fractured limestone aquifer over several weeks, with head observations being collected at a set of observation wells at several depth intervals in the aquifer. The pumping test was combined with six tracer tests. Two fluorescent and two ionic tracers were injected through the screens of the observation wells and monitored at the pumping well. Before the pumping test, the geology was carefully mapped using borehole cores, flow logs, geophysics etc. 3D modeling guided with the test design and helped with the interpretation of the of the pumping and tracer test results.

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.

Identifying Key Parameters Controlling Heat Transport in Discrete Rock Fractures

Issam Bou Jaoude
Understanding heat transfer in fractured rocks is necessary for the proper design of thermal remediation of contaminated sites and the design of energy storage. Numerical modeling of heat transfer, in low porosity fractured rock, is challenging because of the complexity associated with the interaction between fracture, matrix, fluid and the heat source. Of particular importance are the following five parameters; the source configuration, the thermal conduction in the matrix, the velocity of fluid in the fracture, the aperture of the fracture, and the thermal dispersion in the fracture. In this investigation we use factorial analyses (2K) to define which of the five parameters, or combination thereof, significantly influences heat migration in a single fracture setting (parallel plate condition). A 60m block domain was considered with a single horizontal fracture dividing the domain in half. A 10°C uniform temperature was initially set for the model. Two types of constant 11°C heat sources were considered with a point source located in the middle of the fracture, and a line source extending 1 m into the matrix along either side of the fracture. The flow in the matrix was assumed to be extremely small, with isotropic thermal conductivity varying between 0.52 W/m °C and 10.17 W/m °C. The fracture aperture ranged between 100 μm and 2000 μm with velocity varying between 40m/day and 0.5m/day. Thermal dispersivity in the fracture was varied between 1 m and 0.1 m for the longitudinal direction and tenfold less for the traverse direction. HydroGeoSphere was used for the simulations. For the parameter ranges investigated, preliminary results indicate that the most influential factors controlling the heat propagation inside a single fracture setting are the velocity of the fluid in the fracture, fracture aperture size and matrix conduction. Therefore, these parameters should be given better consideration during site characterization.

In Situ Characterization of Processes Controlling Long-Term Release of CVOCs from Low-Permeability Zones

Daniel J. Goode
The U.S. Geological Survey and the University at Buffalo, in cooperation with the U.S. Navy and the Strategic Environmental Research and Development Program, are developing a field method for characterization of diffusion, sorption, and reactions of chlorinated volatile organic compounds (CVOCs) in low-hydraulic-conductivity (low-K) strata. Although CVOC migration in groundwater is attenuated by diffusion and sorption in low-K strata, such strata can also act as long-term secondary sources. The method involves monitoring tracer concentrations in packer–isolated, 2-foot-thick, low-K intervals of open boreholes, in which advective transport is minimal, and estimating reaction rates and diffusion and sorption coefficients by inverse modeling. Proof-of-concept field testing has been conducted in monitoring wells open to mudstone rocks that underlie the former Naval Air Warfare Center (NAWC) in West Trenton, New Jersey. High concentrations of trichloroethene (TCE) and its degradation products (DPs) have persisted in groundwater at NAWC, despite decades of natural attenuation and remediation pumping. A test using conservative and reactive tracers was conducted by gas-stripping volatile components, including TCE and its DPs, from the packer-isolated-interval water and adding the tracers to the isolated zone. The reactive tracer trichlorofluoroethene (TCFE) is considered an analog to TCE for estimating sorption coefficients and reaction rates, for both biotic (biodegradation) and abiotic reactions. Low-volume water samples were collected using peristaltic pumping, closed-loop tubing, and syringes to prevent exposure to air. The same volume of preserved borehole ‘make-up’ water was injected into the test interval to maintain a constant water volume in the system. Gradual, but substantial, changes in tracer concentrations were measured during field tests lasting less than 3 months. Use of the zero-net-volume water-sampling method minimized artifacts associated with advection into and out of the isolated interval, but some fluctuations in the measured concentrations, possibly due to dilution and incomplete mixing, were observed.

Investigation of Hydrogeologic Impacts at Two Historic Landfills Overlying Fractured Bedrock in the Lower Hudson Valley, NY

William, A. Canavan, PG
Investigation of two types of landfills, a construction and demolition (C&D) debris landfill and a municipal solid waste landfill, overlying two separate bedrock lithologies provides evidence for the ability of these types of groundwater regimes to mitigate and prevent the migration of contaminants to the underlying bedrock aquifer. A marble quarry turned municipal landfill for 50 years was investigated as part of the New York State Department of Environmental Conservation (NYSDEC) Brownfield Cleanup Program (BCP). An illegally created C&D landfill overlying metamorphic rock in close proximity to a New York City Department of Environmental Protection (NYCDEP) reservoir was investigated as part of a proposed landfill closure plan. The investigations included installation of multiple monitor wells in the landfill material (overburden aquifer) and the underlying regional bedrock aquifers. Both investigations included coring the underlying bedrock to determine the relationship of secondary permeability features in the bedrock to the overlying landfill material. Primary constituents of concern in the municipal landfill material included volatile organic compounds (VOCs [PCE and TCE]), semi-volatile organic compounds (SVOCs) and heavy metals while constituents of concern in the C&D landfill included SVOCs and metals. Extensive groundwater monitoring and sampling of the monitor well arrays was completed to establish vertical and horizontal gradients between the two aquifers and groundwater flow direction across the landfills. The results of the two investigations indicated that constituents of concern in the landfill material were predominantly not found in the groundwater moving through the bedrock, nor was there evidence that contaminants travelled through the bedrock to the adjacent reservoir near the C&D landfill. The information garnered in both investigations was used to work with the regulatory agencies in the design of a landfill cap and BCP cleanup.

Quantification of LNAPL Transmissivity in Fractured Porous Media

J. Michael Hawthorne, PG
Light Non-Aqueous Phase Liquid (LNAPL) transmissivity is a metric to quantify the hydraulic recoverability of LNAPL. Existing methods to measure LNAPL transmissivity are applicable to granular porous media and often fail to reliably quantify LNAPL transmissivity in fractured porous media. LNAPL transmissivity calculations in fractured porous media require measurement of the geometry and discharge rate for individual fractures containing mobile LNAPL. A modification of methods designed for granular porous media has been developed to provide improved measurement of LNAPL transmissivity in fractured porous media at the individual fracture and aggregate well scales. A second benefit of the process is the high resolution definition of individual fractures containing mobile LNAPL.

Weathering, Structural Style and Frequency in Fractured Bedrock Contaminant Source Areas at Two Sites in the UK

Kevin Leahy, Ph.D.
Case studies are presented of two superficially similar fractured bedrock sites in the UK, both subject to impacts from chlorinated solvent spills. The sites were investigated using high resolution site characterisation techniques which have allowed a detailed understanding of the behaviour of contaminant mass in the source areas. Despite the similarities, differences in the amount of weathering, the structural style and the amount of organic carbon present meant that the contaminant fate and transport at each site is completely different. At one site deep, pervasive weathering had increased matrix porosity and permeability, whilst clay infilled fractures in the underlying fresh shale prevented the contaminants from entering the structures at depth and produced a shallow and relatively short plume. Peaty soils, co-spilled hydrocarbons and the relatively high organic carbon content of the shale had caused extensive dechlorination, such that the parent solvent was usually present at concentrations one order of magnitude lower than the degradation compounds. At the second site there were very thin soils over a low grade slate with almost no weathering, and solvent had penetrated to greater depths and diffused into the matrix at high concentration. A lack of pore space, rapidly consumed carbon sorption sites and little to no biodegradation has produced a deep, long, fast-moving and highly concentrated plume that is impacting a nearby surface water receptor. Both sites are described by site-specific conceptual site models, as well as by standard 14-compartment models of phase and location. The decision to obtain high-resolution structural logging and chemical sampling data were the most important choices in the improvement of the conceptual site model, and ultimately in the selection of a sustainable remedial option.

Contaminant Transport, Remediation and Monitoring

Ryan Wymore, PE

Monitoring the Distribution of a Groundwater Remediation Reagent in Fractured Bedrock with Water Quality Sondes

Adam Hobson, PG
Remediation of contaminated groundwater is often a prolonged and expensive process from initial characterization to achieving remedial action objectives. Rapid assessment of the performance and effectiveness of remedial technologies can shorten the remediation process resulting in reduced costs, reduced contaminant exposure, and thus reduced corresponding risk. In this case study, a monitoring program was implemented to rapidly assess the migration of an in situ groundwater remediation technology applied to contaminated groundwater in shallow fractured bedrock under an active manufacturing building. Due to the manufacturing activities, access to the subsurface with vertical wells or other technologies was not practical, resulting in a limited understanding of the fate and transport of the contamination. To remediate the contamination, injection of a remediation reagent composed of fine particles of activated carbon was proposed. Due to the restricted access, the reagent would be injected along the perimeter of the building and up-gradient of the suspected source area. Initially, monitoring the effectiveness of the remedial solution was proposed to be through quarterly groundwater quality sampling of selected near-source down gradient wells. However, this approach would result in over one year of monitoring, analysis, reporting, and decision making to establish the effectiveness of the remediation. In an effort to accelerate the remediation process and avoid unnecessary delays, we deployed a network of water quality sondes and telemetry units to measure turbidity as a surrogate for the presence of the remediation reagent. Using the near real-time data, we rapidly demonstrated the limited and irregular distribution of the reagent to the target remediation zone (which was subsequently borne out by the groundwater quality sampling), and gained a better understanding of the groundwater flow system, thereby guiding future corrective actions and reducing delays in the remediation process.

Quantifying Mobilization of Chlorinated Ethene Compounds Following Bioaugmentation in a Fractured Mudstone

Allen Shapiro, Ph.D.
Remediation technologies are often applied in fractured rock; however, it is challenging to evaluate their effectiveness with sparse monitoring that is typical in these heterogeneous geologic environments. Monitoring geochemistry usually entails boreholes that target individual or closely spaced permeable fractures. However, the primary porosity of the rock (or rock matrix) is likely to retain the majority of contaminant mass due to diffusion from fractures. Monitoring changes in geochemistry in the rock matrix is not economical because of the high cost of collecting rock cores.

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.

Contaminant Transport, Remediation and Monitoring cont.

Ryan Wymore, PE

Bioaugmentation for Groundwater Remediation of Mixed Chlorinated VOCs in a Fractured Shale Aquifer

Kevin Kelly, PG
Bioaugmentation technology was applied to a mixed plume of chlorinated ethenes and methanes, primarily dissolved trichloroethene (TCE) and carbon tetrachloride (CTC), in a residual source area at the head of a 132-acre plume. This study demonstrates the notable effectiveness on CTC and chloroform in fractured rock, the challenges with commingled TCE, the importance of high-resolution hydrogeologic characterization in remedial design, and the need for targeted and advanced performance monitoring.

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

Matthew Morris
This study demonstrates the design and benefits of using advanced geochemical and microbiological monitoring to evaluate bioremediation performance in a fractured rock environment. Bioaugmentation technology was applied to a commingled plume of chlorinated ethenes, primarily dissolved trichloroethene (TCE), and chlorinated methanes (carbon tetrachloride (CTC) and chloroform), in a fractured rock residual source area. Monitoring showed the notable effectiveness on CTC and chloroform, however understanding the challenges on remediating the commingled TCE and optimizing the design was the real value of advanced monitoring techniques.

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.

Tools and Equipment Necessary for Successful Bedrock Remediation

Ray Boyle
In the last 3 years, the RPI Group has characterized and conducted in-situ remediation at 6 bedrock sites. The synergy of proper characterization using some combination of the tools mentioned below, and effective remediation using either BOS 100® or BOS 200® (depending on the type of contaminant) has resulted in achieving site-specific clean-up standards for one site and full site closure for five sites. All of the sites utilized tactfully placed 6-inch diameter boreholes. Borehole geophysics were applied using carefully chosen tools; including optical or acoustical imaging, fluid temperature, fluid conductivity, and caliper logs to identify zones of transmissivity and potential contaminant migration. A custom designed straddle packer with an 18-inch sample interval was used to acquire discrete samples leading to the knowledge of the vertical distribution of the contaminant mass. Borehole fluid chemistry was monitored until chemical stability was achieved prior to sample collection. It is with knowledge of the vertical chemistry changes that a properly designed injection plan could be devised to place the right amount of treatment at depths of known contaminant mass and concentration. Under dosing and overdosing of the treatment was thus greatly reduced.

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.

High-Resolution Characterization in Fractured Rock

Kenneth J. Goldstein

Comparing Rock Matrix Contaminant Profiles Downgradient of a DNAPL Source after 10 Years of Groundwater Dissolution

Jessica Meyer, Ph.D.
Prior to 1970, over 70,000 L of dense non-aqueous phase liquids (DNAPLs) were released into the subsurface at a site in south central Wisconsin. The mixed organic DNAPL migrated through unconsolidated glacial sediments and shallow sedimentary bedrock, eventually accumulating about 56 meters below ground in a fractured sandstone. The objective of this study was to characterize the temporal evolution of contaminant mass in the source zone by comparing two co-located rock core volatile organic compound (VOC) concentration profiles, one collected in 2003 and the other in 2014. The rock core VOC profiles provided depth discrete and detailed (at least 1 sample/foot of core) quantification of the contaminant mass in the rock matrix. The 2003 core shows relatively uniform rates of mass accumulation with depth for most contaminants; whereas, the 2014 core shows highly variable rates of mass accumulation with depth, particularly in the shallow rock units. These results indicate variable attenuation rates for specific depth horizons. Comparison of total mass estimates for each core indicate an apparent mass loss of ~ 80%, most of which occurs in the shallow bedrock units. Assessment of specific contaminants shows declines in concentration for parent ethanes and ethanes, dichlormethane, and MIBK and increases in concentrations for daughter products (e.g., chloroethane, vinyl chloride). Core and borehole geophysical logs and hydraulic testing provide site-specific parameters for evaluating the role of various attenuation processes (e.g., dispersion, diffusion, sorption, abiotic and biotic degradation) influencing source zone fluxes and longevity. The insights from this temporal comparison will inform a process-based site conceptual model and improve remedial technology assessments.

Conceptualization of Contamination Using Depth Discrete Monitoring of Dynamic PCE Conc. Changes During Pumping

Mette M. Broholm
PCE contamination in a fractured limestone aquifer at a former dry cleaning facility has undergone pump and treat (P&T) with re-infiltration for 10 years after partial source removal. The pumping and re-infiltration has diverted the groundwater flow, and hence the transport of PCE, in the fractured limestone aquifer adding to the complexity. The objective of the investigations was to generate a conceptual model for the residual contamination in the limestone aquifer at the site for optimization of the remediation. The conceptual model is based on the understanding of flow and transport processes in fractured limestone and high resolution data on the PCE distribution and dynamic concentration changes under different pumping schemes. The high resolution data was interpreted by support of a calibrated 3D site specific fracture model.

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.

Fracture Network Characterization: From Active Mine Sites to Subsurface Geological Models

Alena Grechishnikova
Accurate characterization of fracture networks is an important component in developing 3D geological models that predict the pathways for the interaction of surface waters and groundwater resources at mining sites. Natural resources managers dealing with source water protection, watershed management, and environmental compliance monitoring can benefit from the integration of new technologies to map discontinuities (fractures, joints, etc.) in geological reservoirs.

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.

High-Resolution Stratigraphy, Geophysics, and Rock Core Testing to Optimize a Bioremediation Remedy

Robert M. Bond, P.G.
The implementation of a bioremediation remedy for a bedrock contaminant plume is a significant undertaking both in terms of effort and cost and technical complexity. To ensure the success of the remedy, it is vital that the design is appropriate for the geologic conditions encountered at the Site. Several approaches were utilized to develop a high-resolution conceptual model of the injection zone and better characterize the remediation target zones via methods such as borehole optical and acoustic televiewers, caliper, natural gamma, heat-pulse flow meter, bedrock topography, tracer studies, short-term pumping tests, straddle-packer testing, pilot bioremediation injection analysis, rock core analysis and 3D visualization.

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

Carl Keller
Key contaminated site characterization questions are: 1) where are the contaminants in the system; 2) where are the primary pathways for contaminant transport; and 3) how to limit effects of the borehole? A convenient answer is a sealing flexible borehole liner, which includes a NAPL sensitive cover on the liner, and also provides a high resolution profile of the dissolved phase contaminant distribution. This paper presents results of recent field testing of two technologies that can be deployed simultaneously on a FLUTeTM liner. A NAPL FLUTeTM color reactive cover plus an activated carbon felt strip sewn into the interior surface of the NAPL FLUTe cover maps the NAPL and the dissolved phase of contamination. The combination is called a NAPL/FACT.TM FACT is short for the FLUTe Activated Carbon Technique*.The activated carbon felt strip adsorbs by diffusion the dissolved phase of the typical chlorinated solvents and also the daughter products. The carrier liner presses the FACT against the borehole wall, where the carbon felt wicks contaminants from both the pore space of the rock by diffusion and from groundwater flowing in fractures. After two weeks, the NAPL/FACT is recovered by inversion from the borehole. The carbon strip is sectioned into short intervals of generally 0.5-3 ft, which are sent to a lab for analysis using methanol or pentane extraction and a GC/MS system, with results reported as mass of each VOC per mass of dry felt. The NAPL FLUTe cover provides a 2-D map of the NAPL in vicinity of the borehole wall. This paper provides recent results of FACT measurements at the NAWC site near Trenton, NJ including comparison with multi-level water, core, head, and transmissivity profiles in the same borehole. Potential perturbations of the FACT results are addressed. More testing of the technology is ongoing as an ESTCP project

Percolation of Fracture Networks and Stereology

Pierre Adler
The overall properties of fractured porous media such as permeability and transport depend on the percolative character of the fracture network.

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.
It is well known that diffusion driven mass transfer between fractures and the rock matrix controls plume transport and fate in fractured sedimentary bedrock aquifers. Effects can be positive since mass transfer from groundwater flowing in fractures to the rock matrix reduces rates of plume migration and mass flux to receptors, and negative since mass stored in the matrix acts as an impediment to groundwater restoration. While much attention has been focused on chlorinated solvents, there has been little focus on matrix diffusion effects at metals contaminated sites. This study involves a Superfund site in New Jersey, where a hexavalent chromium plume emanates from a former electroplating facility and migrates within a fractured mudstone aquifer discharging to a river. Hexavalent chromium is a contaminant of concern at many sites and can be highly mobile in aquifer systems; however redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to immobile Cr(III) precipitates. A discrete fracture network (DFN) framework was applied for characterization, including collection of detailed profile of Cr mass distribution in the low permeability matrix by subsampling continuous cores with development of new laboratory extraction techniques to quantify both mobile Cr(VI) in porewater and Cr(III) precipitates. Supporting field data included geophysical and hydrophysical methods for fracture network and flow system characterization and installation of a multilevel system for depth-discrete hydraulic head and groundwater sampling for Cr(VI), hydrochemistry and Cr-isotopes. Results show matrix diffusion and reaction processes are influencing the plume including Cr(VI) reduction and immobilization in the rock matrix as Cr(III), which can significantly enhance plume attenuation in combination with matrix diffusion and limit potential for back diffusion if the reduction is irreversible. This presentation will provide an update on study results and implications.

Role of Geophysics in Fractured Rock Characterization

Kent Novakowski, Ph.D, PG

Fiber Optic Distributed Acoustic Sensing (DAS) for Hydraulic Characterization in Fractured Bedrock

Matthew Becker, Ph.D.
A new method is presented for measuring hydraulic connectivity and hydromechanical strain in fractured bedrock. Fiber optic Distributed Acoustic Sensing (DAS), designed for measuring seismic or acoustic vibrations in the Hz-kHz frequency, is used to measure pressure oscillations in the mHz frequency. Induced periodic head oscillation in a source well is observed as strain response (fracture dilation/contraction) in a fiber optic cable installed in a monitoring wells. The fiber optic cable is mechanically coupled to the borehole walls to allow strain to be measured along the entire length of the fiber optic cable. Because the depth of hydraulic response is rarely known a priori, the ability to collect distributed strain response along the length of a borehole is a tremendous advantage for high resolution hydraulic characterization in fractured bedrock.

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

Michael Albright
Karst hydrogeology and geomorphology create unique challenges for effectively characterizing contaminant nature and extent at Kentucky Underground Storage Tank (KY UST) sites. Traditional characterization of KY UST releases in karst terrain involved the initial collection of soil samples (saturated and unsaturated) and groundwater samples from the water-table aquifer. For karst sites with contamination extending to the top of carbonate bedrock, monitoring wells were historically installed into rock without first considering the features of the underlying karst geomorphology and the complex flow dynamics of the karst hydrogeology. Wells installed in this manner can provide inadequate information regarding the following critical bedrock elements: i) Transition zone (epikarst) between unconsolidated material and competent carbonate bedrock; ii) Characteristics of the fractured competent carbonate bedrock below the epikarst; iii) Contaminant mass within the epikarst and fractured rock; and, iv)Flow dynamics and contaminant transport mechanisms of the karst bedrock. The complexity of karst environments also creates challenges for selecting and implementing appropriate remedial technologies. Remediation of contaminated soils can be achieved through removal or in-situ treatment; however, remediation of contaminant mass in epikarst, solution-enlarged bedding planes, and deeper karst conduits remains challenging. Several case studies from KY UST sites demonstrate the critical importance of implementing surface and borehole geophysical technologies for characterizing karst hydrogeology and effectively remediating contaminant mass in karst systems. The case studies describe surface geophysics technologies (e.g. two-dimensional electrical resistivity imaging, refraction microtremor, frequency domain electromagnetic conductivity, very low frequency electromagnetics, etc.) and borehole geophysical methods (e.g. caliper, gamma log, borehole resistivity, optical televiewer, acoustic televiewer, heat-pulse flowmeter, etc.) used to adequately characterize and effectively remediate karst features serving as reservoirs and preferential contaminant transport pathways at KY UST sites.

Welcome and Keynote

William Alley, Ph.D.

Wells, Water Supply, and Recharge in Fractured Rock

Kent Novakowski, Ph.D, PG

A Vertically Compartmentalized, Fracture-Zone, Sandstone Aquifer System

Todd G. Umstot
A south-dipping sandstone formation in the steeply sloping Santa Ynez Mountains near Santa Barbara, California, appears to be divided into vertically-compartmentalized fracture zones. Observations and testing suggest that each subhorizontal fracture zone acts as an aquifer, with limited vertical communication between adjacent aquifers through intact sandstone matrix and the occasional subvertical fracture. Observations include drilling history, well logs, head measurements, and aqueous geochemistry and isotopes, while testing includes geophysical surveys and well tests. Together the multiple fracture zones constitute a vertically-compartmentalized aquifer system supplemented by storage in the matrix and recharged at higher elevations. Normal faulting limits downgradient, southerly flow. The fault barrier, steep slopes, dipping beds, high-elevation recharge, and vertical compartmentalization lead to significant artesian heads in individual aquifers, each of which can be tapped for water supply, apparently without significant interference between aquifers

ITRC’S Guidance for Characterization and Remediation of Fractured Bedrock

Ryan Wymore, PE
After decades of contaminated site characterization and remediation, our understanding of the distribution, fate, and transport of contamination, and implementation of remedial technologies have improved such that numerous sites are reaching remedial objectives. Many of the remaining sites are those with contamination is present in fractured and weathered bedrock. To help address the challenges present at these sites, the Interstate Technology and Regulatory Council (ITRC) has created Technical and Regulatory Guidance on Characterization and Remediation of Fractured Bedrock. This presentation will provide a summary of this guidance document, which will be published in the fall of 2017.

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.

Tracing Seasonal Snowmelt Recharge in Three Distinct Fractured Rock Field Sites with Thin Overburden Using Oxygen and Hydrogen Isotopes

Stephanie Wright
The unique isotopic signature of oxygen and hydrogen in snowmelt is being used as a tracer for recharge to depth in a fractured rock aquifer system. Arrival time and residence time of the isotopic tracer may reveal rates of recharge as well as transport mechanisms for surface contaminants. Three geologically distinct field sites in eastern Ontario are being used to compare these mechanisms in an Ordovician limestone, Precambrian crystalline rock and a gneissic formation. These sites are overlain with thin or no overburden and range in topography from flat-lying to artesian conditions. A total of seven multi-level wells across the sites are being used to trace two snowmelt events that occurred in February and April, 2017. The wells range in total depth from 90 feet to 180 feet. Lysimeters are installed at the soil-bedrock interface to obtain isotope samples of recharge entering the bedrock system after undergoing soil attenuation. Snow and rain were also collected to quantify attenuation of the seasonal isotopic inputs. Current trends in the wells show rapid, but highly attenuated signals following the melting events. However, some wells in the gneissic and Precambrian formations show prolonged response to snowmelt initially in the shallow intervals and two months later in the middle and deep intervals. As of mid-July, these wells continue to decrease in isotopic value, indicating long-term response to snow melt. Potential mechanisms for the observed responses continue to be explored, but may include overburden thickness, local versus regional recharge and multiple fracture contributions at varying quantities and rates. Sampling will continue bi-weekly with updated results and conceptual models presented at the conference.