Roger Beckie

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Application of molybdenum (and zinc) stable isotopes to trace geochemical attenuation in mine waste (2018)

Mining activities generate tremendous quantities of waste rock and tailings that must be carefully managed to prevent contamination of water resources by metal-leaching. Proper environmental management of mine drainage requires a detailed understanding of the mechanisms that control the mobility of metals in mine waste. This thesis applied stable-isotope analyses of molybdenum (Mo) and zinc (Zn) to constrain the geochemical attenuation processes controlling transport of these metals in mine waste. The key outcomes of this work are: (1) the establishment of a robust protocol for determining high-precision Mo isotope ratios in mine-waste samples using double-spike multi-collector inductively coupled plasma mass-spectrometry; (2) the demonstration that mine drainage at field sites becomes enriched in heavy Mo isotopes because Mo attenuation preferentially removes light isotopes; the predominant Mo attenuation mechanisms considered being sorption onto (oxyhydr)oxides and precipitation of molybdate minerals; (3) the demonstration that mine drainage becomes depleted in heavy Zn isotopes under alkaline pH conditions because of preferential removal of heavy Zn isotopes during Zn adsorption and/or precipitation of secondary minerals; and (4) the determination of new Mo isotopic fractionation factors for the precipitation of powellite (CaMoO₄) and wulfenite (PbMoO₄)—important sinks of Mo in mine waste environments. Overall, this thesis demonstrates that metal stable isotope analyses are an informative new tool now available to trace the processes that control metal transport in the environment. Further improvements in the quantification of metal removal using stable isotopic analyses should become possible with ongoing research into the causes of metal stable isotope fractionation.

View record

Unsaturated hydrology, evaporation, and geochemistry of neutral and acid rock drainage in highly heterogeneous mine waste rock at the Antamina Mine, Peru (2014)

Physical and geochemical heterogeneities in mine waste rock complicate the prediction and assessment of waste rock effluent water quantity and quality. The objective of this research is to provide a holistic conceptual understanding of the hydrological and geochemical processes that control effluent water quantity and quality, and the complex interactions among processes at the field scale. To this end, a prodigious dataset from three experimental waste-rock piles at the Antamina Cu-Zn-Mo skarn-deposit mine was compiled and analyzed. Analyses included solid-phase mineralogy and physical characteristics; effluent and pore-water hydrology and geochemistry; and an aqueous tracer study.The instrumented piles (36 m x 36 m x 10 m) are each composed of a single rock type and are exposed to almost identical atmospheric conditions, isolating the effect of rock type on hydrological regimes. Physical waste rock heterogeneities result in highly variable hydrology that is strongly dependent on material particle size distributions and especially the presence of large boulders. The hydrological regimes include wide ranges of velocities for matrix flow (
View record

A field investigation characterizing the hyporheic zone of a tidally-influenced river (2010)

This research investigated groundwater surface water interaction (GWSi) of the Fraser River, in the Lower Mainland of British Columbia. At the Braid Street site, GPR, seismic reflection surveys, bulk resistivity profiling, and sediment sampling were used to map the sediments of the riverbed and the area of contaminated groundwater discharge. Groundwater profiling revealed that three water types occur within the upper 2 m of the riverbed sediments a result of mixing of river water, contaminated (fresh) groundwater, and saline groundwater. The distribution of groundwater solutes indicate that during a single tidal cycle, river water penetrates the riverbed to a depth of approximately 15 cm but the long term effects of tidal pumping of river water into the riverbed is observed to a depth of approximately 1 meter below river bed (m.b.r.b.) Temperature measurements coupled with independent hydraulic head measurements within the riverbed confirmed that GWSi under tidal forcing produced a 1 m-deep hyporheic zone (HZ). Time-averaged riverbed temperature profiles displayed a distinct compressed convex-upward pattern, clear evidence of net groundwater discharge. However, the instantaneous time series data indicate that riverbed temperatures, to a depth of 1 m were affected by tidal-forcing. Heat transport modeling revealed that instantaneous velocities within the shallow sediments of the riverbed are rather high during either a flooding or ebbing tide. Further, the magnitude of the tidally-induced pressure gradient was found to be significantly greater than the pressure gradient attributable to flow across large river bottom bedforms, indicating that bedform-driven exchange is limited to within a few centimeters beneath the riverbed. At the Kidd2 site, where saline encroachment occurs up river, hyporheic and hypoaigic (recharge by saline water) processes occur. During low winter river flows saline encroachment up river occurs and hypoaigic exchange dominates. During low tide the saline water is pushed out of the river and hyporheic exchange dominates. Hyporheic exchange dominates exchange during freshet leading to deep freshening of the aquifer on the order of 2+ m.

View record

Particle and streamline numerical methods for conservative and reactive transport simulations in porous media (2010)

Reactive transport modeling has become an important tool to study and understand the transport and fate of solutes in the subsurface. However, the accurate simulation of reactive transport represents a formidable challenge because of the characteristics of flow, transport and chemical reactions that govern the migration of solutes in geological formations.In particular, solute transport in natural porous media is advection-controlled and dispersion is higher in the direction of flow than in the transverse direction. Both characteristics create difficulties for traditional numerical schemes that result in numerical dispersion and/or spurious oscillations. While these errors can often be tolerated in conservative transport simulations, they can be amplified in presence of chemical reactions resulting in much larger errors or unstable solutions.In this thesis, new Lagrangian based methods to simulate conservative and reactive transport in porous media are investigated. First, the derivation of a new meshless approximation based on smoothed particle hydrodynamics (SPH) to simulate conservative multidimensional solute transport, including advection and anisotropic dispersion, is presented. Second, a hybrid scheme that combines some of the advantages of streamline-based simulations and meshless methods and that allows simulating longitudinal and transverse dispersion without requiring a background grid is also derived. The numerical properties of both methods are analyzed analytical and numerically. Furthermore, both formulations are compared with existing numerical techniques in a set of two- and three-dimensional benchmark problems.It is demonstrated that the proposed schemes provide accurate and efficient solutions of physical transport processes in heterogeneous porous media and overcome most of the issues in existing numerical formulations. The new methods have the potential to remove or minimize numerical dispersion and grid orientation effects and, in the case of the hybrid streamline method, also eliminate spurious oscillations even in presence of large longitudinal to transverse dispersivity ratios.Therefore, the results presented in this thesis confirm that the Lagrangian formulations of solute transport investigated here are viable and compelling alternatives to simulate reactive transport versus more standard numerical techniques.

View record

Monitoring contamination in surface water and groundwater in a catchment with an unconfined porous aquifer overlying fractured bedrock (2009)

The factors influencing the design of an integrated surface water and groundwater contaminant monitoring network are examined for a system where a permeable unconfined aquifer overlies fractured bedrock in a headwater stream catchment. The unconfined porous aquifer is modeled as a homogeneous and isotropic porous medium with deterministic properties. The fractured bedrock is modeled as a lower permeability rock mass, but with a stochastic fracture network composed of three orthogonal fracture sets. The surface domain consists of a V-shaped overland flow zone and a linear stream channel with constant width. A continuous contaminant source zone is situated close to the land surface. The analysis is based on a steady state representation of the groundwater and surface water flow system and transport of a non-reactive solute in both the surface and subsurface domains. The probability of plume detection is defined in terms of the likelihood of detecting contamination in a performance monitoring network prior to its detection at a downstream compliance boundary. The ratio of the permeability of the unconfined porous aquifer to the bulk permeability of the underlying fractured bedrock is a key factor influencing detection probabilities. A higher permeability unconfined aquifer reduces detection probabilities in the stream, and increases detection probabilities in the subsurface. Fracture network connectivity and aperture size have a significant influence on detection probabilities in the subsurface, especially in the bedrock. Dilution of contamination in the headwater stream by inflowing non-contaminated water has a strong influence on detection probabilities. Due to the effect of dilution, sampling both stream water and streambed groundwater will enhance detection probabilities in the stream. The contaminant detection threshold is a key factor in influencing the stream water and groundwater monitoring. A lower detection threshold will increase detection probabilities in the surface water and groundwater systems, especially in the stream water. The results in this study demonstrates the importance of integrating stream water and groundwater samples in the design of a performance monitoring network and documents the factors that determine contaminant detection probabilities in the surface stream, the unconfined aquifer, and the underlying fractured bedrock.

View record

Master's Student Supervision (2010 - 2018)
Biogeochemical characterization of the hyporheic zone below the Fraser River near Vancouver, British Columbia (2016)

The aim of this thesis is to characterize the biogeochemical conditions in the hyporheic zone of the Fraser River in order to help assess the fate of creosote-derived contaminants in groundwater. By investigating hyporheic biogeochemistry, a framework is established for further studies which could quantitatively assess the potential for monitored natural attenuation as a remedial option for groundwater contamination. At our site on the North Arm of the Fraser, groundwater flows horizontally towards the river at a velocity of 0.1 to 0.2 m/day. Transverse mixing between fresh groundwater and underlying saline groundwater is believed to be responsible for cation exchange reactions. From intertidal monitoring wells out to the hyporheic zone (HZ), Fe and Mn concentrations are found to increase despite dilution, and this is believed to be a result of either cation exchange, or oxidation of organic matter (OM), H₂S, or CH₄. As groundwater reaches the river, it turns upward and discharges into the HZ. In the river channel, fresh groundwater discharges to the HZ at distances between 70 and 85 m from the shoreline’s high-water mark (HWM), while the deeper, saline groundwater discharges at distances greater than 100 m. A custom-made cryogenic probe was designed to collect representative, high-quality sediment samples from the HZ. A vertical characterization of biogeochemistry is presented. Chloride is used as a conservative tracer to determine a dilution factor of 170 in the top 85 cm of sediment, but dilution is believed to persist beyond this depth. DNA sequencing results infer a large variety of geochemical processes. Since multiple known aerobic microorganisms are found to have highest proportional abundances in the top 30 cm of the HZ, this depth range is considered to represent the portion of the HZ which is continually exposed to significant amounts of oxygen from the river. Porewater geochemistry also supports this delineation, as Fe(II) is non-detectable above the depth of 30 cm. The estimation of residence time in the HZ, the delineation of the aerobic portion of the HZ, and the characterization of dilution rates provide valuable information on the biogeochemical and physical components of natural attenuation in the HZ.

View record

Iron and manganese reduction driven by organic matter and mixing of fresh and saline groundwater in the Fraser River delta aquifer, Vancouver, Canada (2015)

We present results of field investigations of the biogeochemistry of an aquifer a few km from the ocean adjacent to the Fraser River in Vancouver, Canada. At the site, a wedge of relatively dense saline ocean water enters the aquifer in the hyporheic zone at the river bottom, migrates away from the river along the base of the aquifer to a maximum distance of approximately 500m inland, where it overturns and mixes with fresh groundwater. The mixed saline - fresh water then flows back under a regional freshwater gradient and eventually discharges to the river at the top of the saline wedge. Pore waters show iron concentrations peak at over 300 mg/L (5.4 mM) and manganese at 7 mg/L (0.13 mM) at the upper mixing zone - the interface between terrestrial recharge and top of the overturned saline groundwater. The reducible concentrations on the sediment are approximately 784-2,576 mg/kg (14-46 mM/kg) iron and 110-330 mg/kg (2-6mM/kg) manganese. The dominant process is the reductive dissolution of iron and manganese oxide minerals via organic matter oxidation, although acid-volatile sulfide and methane measurements show that both sulfate reduction and methanogenesis are also occurring. Dissolved organic matter (DOM) concentrations ranged between 5 and 30 mg/L. Excitation – emission fluorescence spectroscopy is used to help identify the distinct sources of DOM, which include terrestrial from fresh recharge, detrital from sediments and from inflowing ocean water. One-dimensional kinetic reactive-transport modeling that includes primary mineral redox reactions and secondary mineral precipitation was used to: i) interpret the role of mixing of fresh and saline water, ii) to constrain reduction-rate parameters and metabolic activity levels from field data, including the oxidation rate of organic matter by iron and manganese oxides, probably accompanied with sulfate reduction and methanogenesis; iii) to understand how other secondary minerals further control aqueous ferrous iron and manganese concentrations through mineral precipitation/dissolution processes; v) to gain insight into the long-term evolution of the geochemistry at the site.

View record

A field cell and humidity cell study of metal attenuation in neutral rock drainage from the Antamina Mine, Peru (2012)

This work focuses on the attenuation of Mo and Zn in neutral pH drainage from waste rock at the Antamina mine in Peru. The study was designed to test the hypothesis that Mo or Zn containing leachate from one waste rock type can be attenuated when allowed to contact a different waste rock type. Mixed material stacked field cells and humidity cells connected in series, where leachate from a Mo or Zn - releasing waste rock type flowed through a second waste rock material type, were used to test this hypothesis. Both of these were new methods, which had not before been reported in the peer reviewed scientific literature related to the study of waste rock geochemistry. Results from both the humidity cells (laboratory conditions) and field cells (field conditions) showed the same general attenuation patterns. When drainage from Mo-releasing waste rock flowed through Pb-rich black marble waste rock, Mo was removed from solution. Mo attenuation was not observed when the order of the waste rock materials was reversed such that drainage from Pb-rich material flowed through Mo-releasing intrusive rock. As, also released from the same Mo-releasing intrusive rock, showed the same attenuation pattern as Mo. Geochemical modeling suggested that wulfenite precipitation was responsible for the observed attenuation of Mo. Zn was removed from leachate both by contact with Mo-releasing intrusive rock and by contact with calcite-rich grey hornfels material. Like Zn, Cd was removed from solution by contact with calcite-rich grey hornfels. Scanning Electron Microscopy (SEM) suggested that Zn may have been incorporated into the crystal structure of phyllosillicate clay minerals; however, further work is needed to confirm this mechanism. Insufficient data were available to develop a hypothesis as to the specific attenuation mechanisms responsible for removing Cd and As from solution.In addition to shedding light on the geochemical processes controlling Mo and Zn in neutral mine drainage, this research also demonstrated the effectiveness of stacked field cells and humidity cells connected in series for the study of metal attenuation by waste rock mixing.  

View record

Hydrogeochemical site characterization and groundwater flow modeling of the arsenic-contaminated Gotra aquifer, West Bengal, India (2011)

Groundwater geochemistry and flow have been studied in Gotra, West Bengal, India, where geogenic arsenic contaminates groundwater at levels above World Health Organization limits. The village is situated upon the natural levee of an abandoned channel, which terminates a fluvio-deltaic depositional sequence. The formerly prograding meander bend deposited point-bar sands during the Holocene that now comprise the 30m-thick shallow aquifer, while incising deeper Pleistocene sands and a shallow floodplain sequence. Hand-pumped tubewells are completed in point-bar sands, whereas irrigation wells are generally screened within Pleistocene materials. Hydraulic conductivity of the point-bar aquifer is approximately 5x10⁻⁴ m/s. A leaky-confining layer of levee/crevasse splay deposits overlies this aquifer beneath crop fields. Near the village, the shallow aquifer is confined by channel-fill silts that have an estimated conductivity of 1x10⁻⁷ m/s. The paleohorizon separating Holocene and Pleistocene sediments is marked locally by fine-grained material comprised of organic material and a hard clay. Groundwater elevations vary 7m over the course of a given year due to monsoonal climate and groundwater extraction. Convergent flow towards shallow pumping wells is a salient feature during irrigation season, and persistent localized downward gradients suggest that meteoric recharge and pumping are the predominant groundwater sources and sinks. A northeast trending geochemical gradient in the point-bar aquifer suggests that local flows transporting arsenic are directed away from the channel-fill silt. Concentration gradients of terminal electron acceptors and redox reaction products in the shallow aqueous profile also coincide with a flowpath originating from this unit. A numerical model of groundwater flow was developed based on a conceptual model derived from field observations to investigate controls of arsenic transport and to provide a context in which to interpret geochemical data. Short- (7-day) and long- (3-year) term transient simulations were implemented to simulate groundwater flowpaths, water balance, and average residence times. Modeling results support field observations that contamination is related to the channel-fill unit deposit, and suggest that the water balance has been significantly altered compared to pre-irrigation conditions. Results also suggest contaminant flushing will not occur over a human timescale.

View record

Microbiology and geochemistry of neutral pH waste rock from the Antamina mine, Peru (2010)

The microbial populations of waste rock piles and field cells producing neutral pH drainage at the Antamina mine were characterized to better understand processes which affect current and future drainage quality. Naturally weathered waste rock samples were collected and examined using a variety of high resolution imaging, geochemical, mineralogical, and microbiological techniques. Despite the relatively young age of the waste rock piles (1.5 years), populations dominated by neutrophilic sulfur oxidizers as large as 10⁸ bacteria per gram were found. An exponential relationship was found between the size of microbial communities and the contemporary sulfate loadings. These results indicate that the microbial populations rapidly grow to reach a mass which is proportional to the rate of substrate release, and then decrease as the host rocks reactivity diminishes. One sample from a field cell producing pH 6.2 drainage had a mixed population of neutrophiles and acidophiles capable of both S⁰ and Fe²⁺ oxidation. A mini-column study was conducted to determine the catalytic effect of microbiology in various rock types. No catalysis was identified in the sulfur concentrations of most mini-column series, with the exception of the one mini-column series constructed of material containing acidophilic S⁰ and Fe²⁺ oxidizing bacteria, which demonstrated strong microbial catalysis. It was also determined that concentrations of Mo as low as 10mg/l were toxic to these acidophilic bacteria, and dissolved Mo may inhibit the establishment of these geochemically important bacteria. A massive sulfide from this material was thoroughly examined using high resolution imaging techniques. Biofilms of bacteria were found upon and within a porous schwertmannite precipitate. The mixed population of neutrophilic and acidophilic bacteria and circumneutral drainage pH implies that the bacteria are living in acidic microenvironments surrounding sulfide minerals in which ferric iron leaching can take place. The large microbial populations and the close correlation between geochemistry and biology described in this study, emphasize the importance of biological processes in determining current and future drainage quality emanating from the mine waste.

View record

 
 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.