Browsing by Author "Butler, Karl"

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    A magnetic susceptibility investigation of the Manicouagan impact structure
    (University of New Brunswick, 2018) Hopkins, Randy G.; Spray, John; Butler, Karl
    The study of terrestrial impact craters provides significant insight as to how hypervelocity asteroid collisions have affected the Earth and other planetary bodies over geologic time. There is still much to learn about the redistribution of material and readjustment of the Earth's crust following an impact event. This study was performed to gain insight of the distribution of magnetic mineral phases within the melt sheet rock as well as study the melt sheet-basement rock interface at the Manicouagan impact structure in northern Quebec. The magnetic susceptibility of two drill cores with a combined length of over 3 km was logged using a KT-10 magnetic susceptibility meter. Magnetic mineral phases within the impact melt sheet were analyzed using Raman Spectrometry. The magnetic susceptibility was found to vary from as high as 577x10-3 SI in basement rocks to as low as 0.01x10-3 SI in the melt sheet. Magnetite was found to be the dominant iron oxide mineral phase within all sections of the melt sheet, except in the upper 190 m of MAN-0608, in which no magnetite was found, and hematite was the dominant iron oxide phase. Offset patterns in the magnetic susceptibility logs of the MAN-0501 and MAN-0608 drill cores of the impact melt sheet suggest that MAN-0501 may have been up-faulted 160 m after the solidification of the impact melt sheet.
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    An electromagnetic survey for groundwater exploration in St. George, New Brunswick
    (University of New Brunswick, 2001) Guidice, Gina M.; Butler, Karl; Karl, Butler
    An electromagnetic survey was conducted near the Town of St. George, New Brunswick in order to explore the area for a possible location for a production well. The survey was conducted in an area south of Lake Utopia where one production well was already located. The survey was conducted using a Geonics EM34 terrain conductivity metre. The metre was used in two modes for measuring which allowed for at least two different penetration depths along each line of the survey. Different penetration depths allow more or less material underground to be studied depending on the orientation of the coils. A theoretical conductivity of clean sand expected to be measured in the field was calculated as being 5.40 mS/m. The survey generated data that indicated where there are areas of high and low electrical conductivities within the 20 to 30 metres of unconsolidated sediments that overly the bedrock in the study site. Areas of low conductivities indicate good locations for water production wells as they are representative of water-yielding sands and gravels. Contour maps were generated for apparent conductivities measured in the horizontal and vertical dipole mode for coil separations of 10 m and 20 m. Apparent conductivities measured ranged from less than 1 mS/m to approximately 13 mS/m. Areas of low conductivities were found to be between lines 15 and 20 of the survey. Onedimensional forward and inverse modelling were carried out at selected locations in order to determine how true electrical conductivity varied with depth. Modelling results agreed within reason with the measured apparent conductivities and the geological information. An upper layer of fine-grained clayey or silty material was observed as thickening as one heads towards the lake along line 20. This fine material may be blocking sand and gravel pores decreasing porosity and leading to a poor hydraulic connection between the aquifer and the lake in this area. It was recommended to the hydrogeologist that, from a lithological viewpoint, the best location in which to drill for a new production well would be between survey lines 15 and 20.
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    Assessment of vadose zone solute transport under a potato field by a 19 month time-lapse cross-hole resistivity imaging survey
    (University of New Brunswick, 2017) Wang, Shuang; Petersen, Brent; Butler, Karl; Danielescu, Serban
    Nitrate is a necessary nutrient for crops, however high concentrations of nitrate in surface water and groundwater can negatively affect aquatic ecosystems and human health. 3D cross-hole Electrical Resistivity Imaging (ERI) has been used to investigate the percolation of a conductive tracer (KCl) through a 17 m thick vadose zone as a proxy for the transport of nitrate under natural recharge conditions. Post-tracer surveys indicate that tracer movement has slowed significantly by early May, 2015 (about one month after tracer application), at the end of snow melt. The shallow conductivity anomaly produced by the tracer diminished significantly over the winter and spring of 2016, but showed little evidence of bulk matrix flow below approximately 6 m depth (top of the bedrock). It is speculated that fractures in the bedrock, too thin to be resolved by the ERI survey, conveyed tracer downward. After 18.5 months, there is no ERI evidence of tracer migrating through the matrix below approximately 6 m.
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    Commissioning a three-dimensional electrical resistivity imaging system for seepage monitoring at an embankment dam abutment
    (University of New Brunswick, 2021) Boulay, Daniel; Butler, Karl
    The Mactaquac Generating Station is a large (660 MW) hydroelectric facility on the Saint John River, approximately 19 km upstream from Fredericton, New Brunswick. An alkali-aggregate reaction within the dam's concrete structures is causing their differential expansion. This has prompted the dam's operator, NB Power, to be proactive in monitoring for any signs of concentrated seepage that could arise where the dam's clay till core abuts a concrete diversion sluiceway. Seepage is a leading cause of dam failures. An emerging method to non-invasively investigate an embankment's interior is Electrical Resistivity Imaging (ERI). ERI is sensitive to changes in water saturation, temperature and ionic content, all of which can be indicators for localized seepage. In this work, a 100 electrode areal array was installed to focus on the interface between the embankment and its concrete abutment. Numerous hurdles and challenges were solved throughout this work. The installation of a durable and effective array was achieved by drilling into the slope and injecting bentonite into the drill holes before driving in long (0.91 m) electrodes to keep contact resistances low. Limitations posed directly by the relatively short survey line lengths on the back of the dam were mitigated by implementing a pole-dipole survey geometry which yields relatively large depths of exploration and maintained sensitivity near the ends of the lines. An enigmatic current regulation issue, which affected repeatability, was solved by customization of measurement array geometries and by averaging many surveys over time with a smart-averaging processing routine designed to reject outlier measurements. Many necessary changes were made to electrode array configuration over the course of the study and data quality has steadily improved. Early results are encouraging, yielding repeatable resistivity models for the embankment that are consistent with its internal structure. Time lapse surveys were successful in observing localized resistivity changes in the embankment, interpreted as seasonal temperature change. Also observed were small resistivity change anomalies within and just outside the core of the embankment, which are inferred to be consequences of changes in saturation and water temperature as well as road salt presence in the winter. Localized seasonal resistivity anomalies have been identified that are suggestive of two paths for elevated seepage: i) water passing through the concrete abutment and entering the rockfill on the downstream of the core, and ii) a possibility of elevated seepage through the core adjacent to the abutment. Further seasonal monitoring as well as incorporating data form electrodes installed across the dam crest will be needed to confidently assess whether seepage through the core is anomalous next to the abutment.
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    Electrical conductivity as a tracer for the migration of lime neutralization sludge in waste rock at the Fire Road Mine, NB
    (University of New Brunswick, 2005) Yeomans, Troy; Butler, Karl; Karel, Butler
    Acid Mine Drainage (AMD) is commonly an unfavorable consequence of strip mining in sulfide rich bedrock. Abandoned strip mining operations, such as the Fire Road Coal Mine in Minto New Brunswick, often require lime treatment facilities to neutralize acidic waters originating in abandoned cuts. Lime treatment produces a metal hydroxide precipitate, lime neutralization sludge, which is collected and stored indefinitely in settling ponds. Since 1992, NB Coal has been attempting to reduce AMD production at the Fire Road Mine (and simultaneously eliminate the need for new settling ponds) by pumping sludge from settling ponds back onto the backfilled cut. It was anticipated that the sludge would plug the void space within the sulphide-bearing waste rock backfill, thereby reducing the flux of atmospheric oxygen into the waste rock and subsequent production of AMD. To date, however, there has been no method short of trenching to determine where sludge migrates and ultimately resides after it infiltrates beneath the surface. In 2004, results of a mine-wide EM 31 apparent conductivity survey suggested that the subsurface migration of the sludge material could be identified. It was speculated that elevated apparent conductivities observed in the immediate vicinity of application sites were indicative of sludge material residing within the void space above the water table. Information on the conductivity of lime neutralization sludge was required to further assess this interpretation. This report focuses on the design and interpretation of laboratory column experiments carried out to determine the electrical conductivity of lime neutralization sludge and to investigate variations in sludge conductivity resulting from changes in moisture content. Column experiments were devised to represent conditions below the water table, at the water table surface, and above the water table. Columns consisted of transparent three inch diameter PVC pipe equipped with potential electrodes along their length and current electrode disks at either end. Initial trials failed due to the formation of cracks in the plane containing the potential electrodes causing partial or complete loss of contact between sludge material and the potential electrodes. Columns were reconstructed with removable electrodes eliminating the plane prone to crack formation. Crack formation was still observed but in an orientation that permitted sufficient contact between the sludge and the potential electrodes. Although electrode contact was achievable, crack formation resulted in non-uniform cross sectional areas and disrupted uniform current flow necessary for mathematical interpretation. Removal of sludge from columns was necessary to obtain reliable measurements towards the end of the experiment. Results obtained from the laboratory experiments indicate lime neutralization sludge at Fire Road Mine has a conductivity of approximately 240 mS/m, similar to that of the mine water. Sludge conductivity decreased as moisture content dropped in response to both evaporative drying and draining of the columns. The laboratory findings help to constrain interpretation of EM field surveys by confirming that the presence of sludge in the vadose zone would have a large effect on field measurements of apparent conductivity. In contrast, the presence of sludge below the water table (where it displaces water of similar conductivity) may not be readily detected. The results support the idea that EM field surveys can be used to infer patterns of sludge distribution and migration within the vadose zone, and may therefore help manage future programs of sludge deposition on the waste rock pile.
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    Field trials of ground conductivity methods for mapping aquitard "windows"
    (University of New Brunswick, 2000) Majid, Naveed Abdul; Butler, Karl; Karel, Butler
    The City of Fredericton relies almost exclusively on groundwater as a source for potable water. However, borehole logs indicate the absence of the protective clay aquitard that overlies the Fredericton aquifer in certain areas. These absences or "windows" may allow contaminants to enter the groundwater supply. Therefore, the Fredericton aquifer is potentially vulnerable to contamination from leaks or spills on the ground Clay, in general, has a cation exchange capacity (CEC), making it conductive. The clay overlying the Fredericton aquifer is more conductive than the sands surrounding it. Resistivity and ground-conductivity methods are two non-invasive geophysical techniques which are sensitive to electrical conductivity. These two techniques accurately, easily and economically image the absence or presence of clay near the ground surface in the Wilmot Park area. The apparent conductivities measured in areas near boreholes and where ground penetrating radar data indicate that the aquitard has been eroded are significantly lower in comparison to the apparent conductivities measured over areas where the clay layer is known to be intact at depths of approximately 5m. The "window" boundary was defined by performing ground conductivity surveys along an extensive grid. Subsurface stratigraphy was modelled using the WinSev5 resistivity depth sounding software and the Ghosh Spreadsheet. In addition, the depth to the top of the clay is estimated based on layered stratigraphic models.
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    Geoenvironmental significance of spectral IP anomalies at two rock cuts along the new TransCanada Highway, central New Brunswick
    (University of New Brunswick, 2003) Bishop, Tineka; Butler, Karl; K., Butler
    The oxidation of aggregate containing even small sulphide concentrations in combination with a water source can produce sulfuric acid and in turn pollute aquatic life and local ground water systems. The adverse environmental impact and high cost of remediating affected areas provide motivation for engineers to identify areas at risk for sulphide oxidation during the highway planning stage. By identifying these zones, they can be avoided or the sulphide-bearing fill can be disposed of in an environmentally friendly manner. Butler and Al (2002) preformed geophysical field trials at two sites along the new TransCanada Highway, and large IP/ resistivity anomalies were seen. The principle objective of this report was to determine if the shape of IP decay curves, as described by spectral IP parameters, "m", "Tau" and "c", could be used as a basis for discriminating the type of mineralization responsible for observed anomalies, especially graphite versus sulphide. The methods used in this investigation included magnetic susceptibility, IP and resistivity measurements. It was determined that the chargeability "Mx" is highly influenced by the sulphide concentration, and in particular, pyrite mineralization. Ilmenite and pyrrhotite were found to produce high magnetic field peaks while the "Tau" parameter was influenced by the total graphite content and specifically the grain size.
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    Gravity modelling of the Marysville, New Brunswick subbasin
    (University of New Brunswick, 2000) Farquharson, Graham; Butler, Karl; Karel, Butler
    This report investigates the economic potential of the Marysville Carboniferous Subbasin using existing regional gravity survey data to estimate sediment thickness and basement shape. The geometry of the Marysville Subbasin (MSB) was investigated by modelling o f existing regional gravity data supplied by the New Brunswick Department of Natural Resources & Energy (NB DNRE). Geologic models for subsurface structure were developed based on a review of Carboniferous Basin geology in New Brunswick. Rock densities were obtained from a New Brunswick DNRE complication (Hassan, 1996) and Thomas and Willis (1989). An 85 km linear profile of Bouguer gravity values at 71 stations across the Marysville Subbasin was imported into a 2.75 dimensional gravity modelling software package in order to model Marysville Subbasin geometry. Pre-existing information on the regional geology of the Marysville Subbasin that helped guide the gravity modelling process included a NB DNRE geology map of southwest New Brunswick (Plate NR-5), and reports by Thomas and Willis (1989), and Spector and Pichette (1980). The observed gravity profile contains a central low over the Marysville Subbasin flanked by highs related to Shin Formation mafic volcanics. The gravity highs on the perimeter of the basin are in turn flanked by lows related to the low density Pokiok and St. George Batholiths. Precambrian basement structure is fault-controlled with subvertical movement on the Fredericton and Belleisle Faults. The maximum depth of the Marysville Subbasin was estimated to be 2.3 km near Fredericton Junction. Gravity modelling o f a hypothetical salt diapir indicated an observable gravity effect only when fully developed and 800 m in height. The Marysville Subbasin contains sufficient sediment thickness to host Windsor evaporites and therefore justifies more detailed geophysical surveys including a gravity component.
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    Influence of mineralogical composition and texture on induced polarization effects in gold-bearing rocks from the Hebert-Brent Showing, Yellowknife Greenstone Belt, Northwest Territories
    (University of New Brunswick, 2017) Richardson, Mark; Butler, Karl; Lentz, David
    In June 2015, geological mapping discovered significant concentrations of gold in the Hebert-Brent (HB) Showing situated within an 11 m-wide highly sulphidized sericite-ankerite schist shear zone, hosted in a 10-15 m-wide, quartz-feldspar porphyry. The HB gold showing is located within the Barney Deformation Corridor of the Yellowknife Greenstone Belt (YGB), Northwest Territories. On July 29th, 2016, two 400 m long IP/resistivity surveys, with 5/10 m electrode spacing were acquired using a multi-gradient array. The survey identified zones of high IP response (chargeability) where expected, in areas of known disseminated sulphide mineralization. In addition, the IP survey exposed a previously undiscovered anomalous IP source. In this study, a prototype two electrode laboratory apparatus was used to investigate factors influencing electrical resistivity and IP effects in selected mineralized and non-mineralized rocks from the survey area. The study revealed information that may be utilized in future geophysical exploration in this area. It was determined that samples from Hebert-Brent are generally less resistive than non-mineralized rocks within this area. However, as a consequence of preferential alignment of silicate layers with foliation, anisotropic effects should be anticipated in this area. The IP response of the mineralized samples was in general greater in magnitude than the non-mineralized samples. It was also determined that there are some IP effects related to highly resistive, non-mineralized rocks in this area. These anomalous IP effects are likely a result of some uncertainty in the measurement apparatus. Normalizing the PFE IP effect by resistivity served to make the mineralized samples standout from highly resistive ones that also exhibited elevated IP responses. Comparison of mineralized and non-mineralized spectral curves were shown to be characteristically different. In addition, the peak phase angle between 0.1 - 10 Hz was found to correlate with increased percent frequency effect. It is recommended that surveys which sense the conductivity of an ore body should be used to aid in delineating massive and electrically conductive parts of a sulphide body. In addition, it is recommended that future IP and resistivity surveys in the area use a measurement of IP effect normalized by resistivity (such as the Metal Factor; MF) to highlight anomalous bodies that are prospective for elevated sulphide (and associated gold) content. Based on the findings in this study, spectral induced polarization (SIP) surveying may aid in identifying mineralized rocks in HB, as the phase maximum (between 0.1 and 10 Hz) is in general greater than that of the non-mineralized country rocks. Testing of the two electrode apparatus was shown to provide accurate and repeatable measurements on both the mineralized and non-mineralized rocks used in this study. However, more testing of the measurement apparatus is recommended to assess its reliability for very highly resistive samples.
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    Influence of mineralogical composition and texture on induced polarization effects in gold-bearing rocks from the Hebert-Brent Showing, Yellowknife Greenstone Belt, Northwest Territories
    (University of New Brunswick, 2017) Richardson, Mark; Butler, Karl; Lentz, David
    In June 2015, geological mapping discovered significant concentrations of gold in the Hebert-Brent (HB) Showing situated within an 11 m-wide highly sulphidized sericite-ankerite schist shear zone, hosted in a 10-15 m-wide, quartz-feldspar porphyry. The HB gold showing is located within the Barney Deformation Corridor of the Yellowknife Greenstone Belt (YGB), Northwest Territories. On July 29th, 2016, two 400 m long IP/resistivity surveys, with 5/10 m electrode spacing were acquired using a multi-gradient array. The survey identified zones of high IP response (chargeability) where expected, in areas of known disseminated sulphide mineralization. In addition, the IP survey exposed a previously undiscovered anomalous IP source. In this study, a prototype two electrode laboratory apparatus was used to investigate factors influencing electrical resistivity and IP effects in selected mineralized and non-mineralized rocks from the survey area. The study revealed information that may be utilized in future geophysical exploration in this area. It was determined that samples from Hebert-Brent are generally less resistive than non-mineralized rocks within this area. However, as a consequence of preferential alignment of silicate layers with foliation, anisotropic effects should be anticipated in this area. The IP response of the mineralized samples was in general greater in magnitude than the non-mineralized samples. It was also determined that there are some IP effects related to highly resistive, non-mineralized rocks in this area. These anomalous IP effects are likely a result of some uncertainty in the measurement apparatus. Normalizing the PFE IP effect by resistivity served to make the mineralized samples standout from highly resistive ones that also exhibited elevated IP responses. Comparison of mineralized and non-mineralized spectral curves were shown to be characteristically different. In addition, the peak phase angle between 0.1 - 10 Hz was found to correlate with increased percent frequency effect. It is recommended that surveys which sense the conductivity of an ore body should be used to aid in delineating massive and electrically conductive parts of a sulphide body. In addition, it is recommended that future IP and resistivity surveys in the area use a measurement of IP effect normalized by resistivity (such as the Metal Factor; MF) to highlight anomalous bodies that are prospective for elevated sulphide (and associated gold) content. Based on the findings in this study, spectral induced polarization (SIP) surveying may aid in identifying mineralized rocks in HB, as the phase maximum (between 0.1 and 10 Hz) is in general greater than that of the non-mineralized country rocks. Testing of the two electrode apparatus was shown to provide accurate and repeatable measurements on both the mineralized and non-mineralized rocks used in this study. However, more testing of the measurement apparatus is recommended to assess its reliability for very highly resistive samples.
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    Investigation of flow and solute transport in a shallow perched groundwater system beneath a potato field
    (University of New Brunswick, 2016) Lamb, Keenan James; MacQuarrie, Kerry T.B.; Butler, Karl
    Intensive potato production in the Canadian province of Prince Edward Island (PEI) has contributed to the leaching of nitrate to groundwater and increased nutrient loadings to surface waters. The presence of a compact till layer at roughly one metre depth is known to cause temporary perched water table conditions, which may result in lateral subsurface flow that may effectively reduce the migration of nitrate to groundwater. The primary objective of this work was to determine the importance of this compact layer to vertical and lateral subsurface flow of water and nitrate. A surface applied tracer test was conducted at the Harrington Research Farm in central PEI. A shallow drain-tile pipe system, with a tipping bucket gauge, was installed down gradient of the tracer application to monitor lateral subsurface flow. A three-dimensional electrical resistivity imaging (ERI) array was employed on surface to monitor the spatial and temporal distribution of the applied tracer. A small scale, transient flow and transport model was constructed to simulate the tracer test. Results from the tracer test monitoring and numerical modelling show that the occurrence of lateral flow is dependent on the antecedent moisture conditions in the subsurface. The water balance yielded a total vertical flow of 94 % of the infiltration for the period beginning October 25, 2014 and ending January 1, 2015. The cumulative observed tracer mass in the tipping bucket as of May 12, 2015 (10.5 months after tracer application) was 0.125 % of the applied mass. The preference for vertical over lateral flow was further evidenced by the electrical resistivity images for the same time period. These results show a strong preference for vertical flow of water and nitrate through the compact layer as opposed to lateral subsurface flow.
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    Investigation of seepage near the interface between an embankment dam and concrete structure: monitoring and modelling of seasonal temperature trends
    (University of New Brunswick, 2018) Yun, Tana; Butler, Karl; MacQuarrie, Kerry T.B.
    The temperature monitoring method, which makes use of the fact that increased seepage flow may locally alter the natural temperature distributions within embankment dams and their foundations, is regarded as a useful approach for seepage monitoring and evaluation. In this study, spatial and temporal variations of temperature have been monitored and modelled at the interface between the compacted clay till core of an embankment dam and an adjoining concrete diversion sluiceway structure at the Mactaquac Generating Station, located on the Saint John River near Fredericton, NB. The measurements were acquired using a fibre optic distributed temperature sensing (DTS) system installed in a 50 m long borehole drilled into the concrete structure within 0.5 m of the interface. Two significant temperature anomalies were observed. A three-dimensional finite element model was developed to simulate the temperature distributions within the dam resulting from the seasonal variations of air and headpond water temperatures. Anomalous seepage zones near the interface were simulated in the concrete and along the dam/concrete interface (in the embankment) independently, and in both locations simultaneously. The results demonstrate that passive DTS monitoring is a feasible approach to identify potential seepage zones near an embankment dam/concrete structure interface. Anomalous temperature zones, and associated gradients, can be clearly identified and numerical modelling can indicate, in some cases, whether such anomalies are related to seepage in the concrete or in the embankment; however, other details such as the water flow path geometries and seepage rates are not as well constrained.
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    Investigation of seismoelectric effects in soft sediments
    (University of New Brunswick, 2003) Kellock, Jason Andrew; Butler, Karl; Karel, Butler
    Field trials of the seismoelectric geophysical method were conducted at two sites along the Saint John River in Fredericton, New Brunswick, Canada. These tests were performed in order to evaluate the suitability of this particular geophysical method for imaging subsurface interfaces in soft sediments in an urban environment. To this end, this method was used to investigate the presence and thickness of the clay aquitard that overlies the Fredericton Aquifer. Seismic refraction and seismic reflection data was collected at the same site for comparison purposes and for use in further studies of the Fredericton Aquifer. The test surveys were conducted at two separate locations over three days during the fall of 2002. Measurements made along the Saint John River west of Wilmot Park (behind the Fredericton Sheraton) were used to verify the operation of the equipment and produce sample results for processing. The survey conducted at Morell Park was the primary focus of the study. Seismoelectric shot records were collected utilizing blank shotgun shell and sledgehammer seismic sources. Extensive processing was required to remove background noise and enhance the signal to noise ratio. In particular, powerline frequency harmonics dominated the raw data and required removal by a specific processing algorithm. The measured electrical signals in the ground in the raw shot records were approximately 0.06 V/m. After processing, the magnitude of the seismoelectric signals were calculated to be approximately 0.002 V/m. The results of the seismoelectric survey were compared with the results of the seismic reflection and refraction survey as well as the available borehole data in order to correlate the results. Bulk and interfacial seismic effects were identified in the processed records.
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    Physical Characterization of two fractured sedimentary rock aquifers in New Brunswick, Canada with emphasis on the development of self-potential methods
    (University of New Brunswick, 2017) John DesRoches, Aaron; Butler, Karl
    Heterogeneity and anisotropy associated with fractured rock aquifers can make predicting fluid flow pathways difficult using traditional hydraulic testing methods alone. Surface-based self-potentials (SP) measured during pumping and hydraulic testing have been shown in this thesis to provide valuable information used to infer water table drawdown, preferential flow paths and hydraulic properties. To provide a basis for investigating the SP approach in fractured rock, conceptual models were first developed for two separate aquifers. Fracture patterns, combined with pump test and geophysical logging data allowed for flow directions to be assessed within a confined fluvial sandstone-shale aquifer underlying the Springdale wellfield in the Carboniferous Moncton Subbasin. In the Ordovician to Silurian Matapédia Basin, fracture characteristics were measured within the folded turbidite sequences underlying the Black Brook Watershed, and combined with hydraulic conductivity estimates derived from packer testing to provide a better understanding of heterogeneity responsible for anisotropic groundwater flow conditions. Both fractured aquifers were subsequently investigated through SP monitoring and numerical modelling. Transient SP signals recorded during pumping in the Springdale wellfield, combined with measurements of the electrokinetic voltage coupling coefficient, allowed spatial and temporal variations in drawdown to be inferred below electrodes positioned around the pumping well. SP-derived drawdown was fitted to the Theis model to obtain transmissivity and storativity estimates at electrode locations. Numerical modelling showed surface SP measurements to be an excellent proxy for hydraulic head at the top of an underlying confined aquifer even in the presence of hydraulic and electrical heterogeneities. SP signals recorded in the Black Brook watershed during a constant head injection test at a depth of 44 m were used to infer azimuthal anisotropy in fluid flow in directions consistent with dominant fracture set orientations. Numerical modelling showed that fracture transmissivity, length, and frequency all contribute to the magnitude and shape of SP anomalies recorded on surface resulting from flow from the highly transmissive fractures into the surrounding rock matrix. Results from the SP monitoring approach, combined with the conceptual aquifer models, demonstrated an inexpensive and non-invasive means of assessing water table drawdown pattern, preferential flow directions, and hydraulic properties estimates without the need for additional wells.
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    Reservoir siltation and quaternary stratigraphy beneath the Mactaquac headpond as revealed by acoustic and ground penetrating radar sub-bottom imaging
    (University of New Brunswick, 2017) Grace, Mitch; Butler, Karl
    The Mactaquac Hydroelectric Generating Station, located on the Saint John River in New Brunswick, Canada, is approaching the end of its life due to deterioration of the concrete structures. As part of an aquatic ecosystem study, designed to support a decision on the future of the dam, physical and chemical characteristics of sediments beneath the headpond, extending 80 km upriver, are being examined. The focus of this sub-study lies in (i) mapping the thickness of sediments that have accumulated since inundation in 1968, and (ii) imaging the deeper glacial and post-glacial stratigraphy. Acoustic sub-bottom profiling surveys were completed during 2014 and 2015. An initial 3.5 kHz chirp sonar survey proved ineffective, lacking in both resolution and depth of the penetration. A follow-up survey employing a boomer-based "Seistec" sediment profiler provided better results, resolving sediment layers as thin as 12 cm beneath up to 40 m of water, and yielding coherent reflections from the deeper Quaternary sediments. Post-inundation sediments in the lowermost 25 km of the headpond, between the dam and Bear Island, are interpreted to average 20 cm in thickness, corresponding to an average reservoir sediment accumulation rate of 4.3 mm/year. The thickest deposits (up to 60 cm, corresponding to a sedimentation rate of 13 mm/year) are found in deep water areas overlying the pre-inundation riverbed west of Snowshoe Island, and south and east of Bear Island. A coring program confirmed the presence of silty sediment and showed good correlation with the Seistec thickness estimates. In the ~15 km stretch upriver of Bear Island to Nackawic, the presence of gas in the uppermost sediments severely limits sub-bottom penetration and our ability to interpret sediment thicknesses. Profiles acquired in the uppermost ~40 km reach of the headpond, extending from a few km upriver of Nackawic to Woodstock, show a strong, positive water bottom reflection and little to no sub-bottom penetration, indicating the soft post-inundation sediment in this region is either absent, or thinner than the 12 cm resolution of the Seistec profiler. Deeper reflections observed within 5 km of the dam reveal a buried channel cut into glacial till, extending up to 20 m below the water bottom. Channel fill includes a finely laminated unit interpreted to be glaciolacustrine clay-silt and a possible esker – similar to stratigraphy found 20 - 30 km downriver at Fredericton. A small scale survey was conducted near Nackawic to evaluate the suitability of waterborne ground penetrating radar (GPR) profiling as an alternative to acoustic profiling in areas of gas-charged sediment. The GPR was able to image thin sediments in the area, showing sediment thicknesses of less than a meter. However due to rapid attenuation of the GPR signal in the water column, this survey method was only viable in the relatively shallow areas near the shoreline, less than 15 meters water depth.
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    Salt water intrusion within a Carboniferous sandstone aquifer at Richibucto, New Brunswick as revealed by hydrogeophysical and petrophysical investigations
    (University of New Brunswick, 2014) Mott, Eric; Butler, Karl
    Hydrogeophysical surveys have been carried out in the vicinity of Richibucto, New Brunswick, as part of a project to assess the risk that salt water intrusion along the Northumberland Strait could increase over time as a consequence of climate change and rising sea level. The surveys involved electrical resistivity imaging (ERI) measurements along several lines extending inland from the coast in conjunction with geophysical logging of two new and several pre-existing boreholes. The investigation indicates that the elevated salinities that have intermittently affected Richibucto’s municipal wellfield are likely a consequence of salt water upconing beneath pumping wells. Evidence of a salt water wedge extending approximately 200 m inland was also observed beneath one ERI line acquired in a particularly low lying area adjacent to Richibucto Harbour. The results illustrate that ERI surveying can be an effective tool in identifying the extent and modes of salt water intrusion in Carboniferous sandstone aquifers that supply water to many coastal communities along the Northumberland Strait coast. Data interpretation is, however, complicated by the presence of relatively thin, discontinuous layers of electrically conductive shale. With core recovered from boreholes, a relationship was established in the laboratory between the bulk conductivity of rock samples and their pore fluid conductivity. With this relationship, along with a relationship of chloride concentration to water conductivity acquired from water sampling, it was possible to estimate in-situ pore water salinity from borehole resistivity measurements.
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    Suppression of water bottom multiples in shallow seismic data by predictive deconvolution
    (University of New Brunswick, 2003) Wei, Chow Song; Butler, Karl
    Predictive deconvolution is a digital signal processing technique widely used to compress the seismic wavelet and remove multiples in seismic reflection data. In this paper, predictive deconvolution is used to suppress water bottom multiples in shallow seismic data collected with the IKB Seistec TM single channel seismic system. These data were acquired in the St John River at Fredericton during the summers of 2001 and 2002. The convolutional model is a method of explaining the origin of reflection seismograms, which are recordings of seismic pulses reflected back to surface from subsurface boundaries between different layers of sediment or rock. Deconvolution is a method of attempting to reverse convolution process and estimate the subsurface reflectivity based on an analysis of the recorded seismogram. In other words, convolutional model is estimate the seismic wave response with the earth reflectivity, but deconvolution is the reverse, finding the reflectivity. Initial tests of predictive deconvolution have proven that partially successful in removing multiples from the marine seismic data set. However, the results have not been as good as we had hoped. We examine field data, synthetic data and the underlying assumptions of the predictive deconvolution process to identity a number of possible reasons for our sub-standard result including (i) the large noise pulse at time zero in our seismic data, and (ii) the fact that our source wavelet does not appear to be minimum phase.
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    Tests of seismic methods for imaging stratigraphy of the Fredericton aquifer
    (University of New Brunswick, 2000) Gilman, Tony L.; Butler, Karl; Karel, Butler
    Seismic test methods for imaging stratigraphy of the Fredericton aquifer were conducted in Wilmot park, Fredericton, New Brunswick. The primary project objective was to investigate the possibility of using seismic refraction techniques to determine the location of clay "windows", in the clay aquitard, of the Fredericton aquifer. The secondary project objectives included recording seismic reflections from bedrock at a depth of approximately 60 m, and measuring shear wave velocities in the clay layer. The engineering properties of clay, such as shear modulus and Poisson's ratio, can be obtained from the velocities. Three seismic methods were investigated, at three locations in Wilmot park, Fredericton, New Brunswick. These methods were p-wave seismic refraction, p-wave seismic reflection, and shear wave refraction tests. These tests were carried out over a three day period in November of 1999. The seismic p-wave refraction data have been interpreted by the generalized reciprocal method (GRM) to yield two depth vs. distance plots. The seismic p-wave reflection data have been interpreted, assuming a single layer constant velocity unit. This yielded a single velocity and depth estimate to bedrock. Data quality obtained for the shear wave refraction was adversely affected by the collection equipment. From this data shear wave velocities were obtained with the hope of estimating engineering properties of the clay, however; due to the poor data quality, this was not possible. Interpretation of the seismic refraction data yielded depths to near surface refractors along these profiles. The depth to clay was estimated at 4.5-5.0 m, which agrees with radar data (Paasche, 2000), and borehole logs in the area. In an area where no clay was believed to be seen the depth to saturated sediments was estimated at 12.0-14.0 m also in correspondence with radar and borehole information. The seismic p-wave reflection initially yielded depths to bedrock of approximately 80m. The actual depth to bedrock as measured in borehole logs is approximately 60m. A possible explanation for this fallacy is the presence of unsaturated sands and gravels of low seismic velocity in the top 5.0 m of the stratigraphy. To correct for this problem, the travel times through the 5 m sand and gravel layer were subtracted from the total travel times, yielding an approximate depth to bedrock of 66m. The shear wave refraction tests yielded shear wave velocities of approximately 154 m/s and 259 m/s respectively, however it is not certain as to weather these velocity are for the clay or the overlying sands.
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    The determination of the suitability of ground penetrating radar to map "windows" in the protective clay/silt aquitard of the Fredericton aquifer
    (University of New Brunswick, 2000) Paasche, John A.; Butler, Karl; Karel, Butler
    Ground Penetrating Radar (GPR) is a non-invasive geophysical technique that can be used to determine the subsurface features at a site. This method utilizes changes in material properties (i.e. conductivity, dielectric constant) to provide a detailed image of the underlying geology stratigraphy. The City of Fredericton's main source of potable water is a glaciofluvial sand and gravel aquifer that is overlain by a lacustrine clay/silt unit of variable thickness and a fluvial sand and gravel deposit. The sites chosen for this investigation are located near the Fredericton well field in the Wilmot Park and Smythe Street area of the City's Downtown. Through previous borehole data (Violette, 1990) available for these locations, the confining clay/silt layer is known to exhibit breaks or 'windows' that can be potential sources of recharge or contamination for the aquifer. It would therefore be useful to locate these 'windows' to prevent possible migration of hazardous material into the water supply and to aid in determining the extent of recharge to the aquifer at these locations. The method of GPR profiling with 50 and 100 MHz antennas proved to be an effective means of determining the presence (or lack) of clay/silt due to the high attenuation caused by this highly conductive lacustrine sediment. The clay/silt layer was interpreted as a strong reflector that appears to have a gently slope to the South. This was evidenced by the fact that the reflector varied from - 8 0 to -105 ns in the N-S profiles (9, 11, 12 and 13). The location of the clay window near Smythe Street and in the Southeast corner of Wilmot Park have been positioned using the interpreted radar data.