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Climate Change Impacts on Water

The Resiliency of Groundwater Systems to Extreme Weather Events (MSc, Nott, in progress). At the forefront of novel research on the effects of climate change on the hydrologic cycle, are the severe, but rarely occurring, extreme weather events. Anthropogenically-driven climate change has unequivocally lead to global increases in the intensity and frequency of extreme weather events – notably, future warming will intensify the extremes in very wet or very dry weather events. This research explores the resiliency of groundwater systems to extreme weather events, by comparing the hydrogeological responses in: (1) a low-land rainfall-dominated catchment, and (2) a mountain-to-valley snowfall-dominated catchment in southwestern British Columbia (BC).  

Nitrate Variability in Groundwater due to Extreme Precipitation Events (MSc, Greenblat, in progress). Nitrate remains the most ubiquitous groundwater contaminant globally. Nitrate loading to aquifers is influenced by the timing and amount of infiltration. However, our understanding of how heavy rain events may affect nitrate loading and subsequent contamination of aquifers is limited. Synoptic sampling of nitrate is being carried out in an agricultural area in southwestern British Columbia following heavy rain events. Stable isotopes of water are being used to distinguish atmospheric river (AR) rain events from non-AR rain events, and potentially distinguish the proportion of recharge from AR storms. 

Reconstructing Groundwater Levels from Tree Ring Widths in the North American Cordillera (PhD, Hunter, 2021) Water resources around the world are periodically impacted by droughts, which can reduce water available for human use and put stress on the environment. The effects of long-term changes in climate on groundwater resources are difficult to determine, as most observed groundwater level records are short (< 60 years). However, observational records can be extended using proxy records such as tree ring widths. This research uses two methods to study past groundwater changes (1850-2002) in the North American Cordillera: a nested principal component regression technique to reconstruct past groundwater levels from tree ring widths, and a nonparametric approach which reconstructs daily temperature and precipitation based on annual tree ring widths, to be used as input into a hydrological model for simulating groundwater levels. The past spatial and temporal occurrence of droughts in this region is examined, as are the associations between past groundwater levels and climate teleconnections. The groundwater level reconstructions demonstrate that the relationships between groundwater levels and snowpack, and tree ring widths and snowpack, are important for creating groundwater level reconstructions in mountain regions. In addition, separating groundwater observation wells by dominant aquifer-stream system strengthens the reconstructions. Analysis of past groundwater drought (between 1850 and 2004) shows that drought events were not synchronous across the North American Cordillera, with variations in timing occurring between the north and south cordillera, as well as between different aquifer-stream systems. Teleconnections patterns that affect observed groundwater levels in this region were also found to influence past groundwater levels. Hydrologic modeling results show that the nonparametric approach was useful for creating simulations of past groundwater levels, and that in the past time periods analyzed (1920-1950 and 1950-1980), peak recharge occurred earlier in the year than in the observed climate; this earlier peak in recharge is likely due to warmer spring temperatures and earlier snowmelt during the paleo-periods. These results show that the relationship between groundwater levels and tree rings can be used to successfully reconstruct and simulate past groundwater levels in mountain regions, providing a long-term perspective into groundwater variability throughout the past. 

Snow Drought and Streamflow Drought in Western North America in the Context of a Warming Climate (PhD, Dierauer, 2018) In western North America, snowpack supplies much of the water used for irrigation and for municipal and industrial uses, and snowmelt recharges groundwater and provides ecosystem-sustaining baseflow during low flow periods. Continued climate warming is expected to have large impacts on snowmelt hydrology, with subsequent impacts on low flows and snow and streamflow drought regimes. This research combined two separate methodologies, a data-driven (downward) approach and a process-based (upward) approach, to improve our understanding of snow drought and streamflow drought in the context of a warming climate. The data-driven approach combined observed hydroclimatic time series with multiple statistical methods, including bivariate and partial correlation and temporal and spatial analogs. The process-based approach combined climate change projections and hydrological modelling. The two approaches yielded consistent results that, together, illustrate that snow drought, low flows, and streamflow drought are sensitive to winter climate conditions, particularly precipitation and thawing degrees. In the context of climate warming, increased winter season thawing degrees leads to increased warm (temperature-driven) snow drought, shorter and less severe winter low flows, longer and more severe summer low flows, and increased summer streamflow drought risk. Further, both approaches showed that the response of snowmelt hydrology to climate warming is non-linear, and regions with winter temperatures near 0°C exhibit substantially larger impacts from +2°C of warming compared to regions with winter temperatures far below 0°C. Temperature-driven shifts in snow drought, low flows, and streamflow drought regimes will have widespread implications for surface water supply security. Increased frequency of warm snow droughts will likely lead to an increased frequency of mid-winter melt events, which will create challenges for water management. As summer low flow periods become more severe and snow-drought related summer streamflow droughts become more frequent, the potential for more severe summer water shortages increases. The most severe shortages will likely occur due to the co-occurrence of warm and dry conditions.

Risk to Water Quality and Quantity

A Morphological Approach to Evaluating Risk to Freshwater Resources in Coastal Deltas (PhD, Anderson, 2023). Coastal deltas house more than 335 million people worldwide in some of the largest population centers in the world, including growing megacities such as Shanghai, Dhaka, and Bangkok. These populations often rely heavily upon groundwater resources to meet domestic, agricultural, and industrial water demands—making the sustainability of fresh groundwater resources critical to ensuring the longevity of coastal communities. This research uses morphodynamic modeling to simulate the formation of coastal deltas and explore how delta morphology impacts hydrogeologic characteristics within deltas. Data from deltas around the world are used to create 207 unique models that span the full range and combination of fluvial and marine influences. Simulated landforms depict the characteristics expected in fluvial, wave, and tidal influenced deltas; these landforms are used to generate spatially varying permeability profiles for each simulated delta. A distance-based sensitivity analysis shows that deltaic permeability, hydraulic gradient, and groundwater flow rates are sensitive to changes in delta morphology and geomorphic characteristics. Two-dimensional density-dependent groundwater flow and solute transport modeling is used to simulate the horizontal fresh-saline water distribution within the shallow subsurface in representative fluvial, wave, and tidal deltas. The volume of saline water in the shallow subsurface within deltas is estimated to vary between 36% and 89% of the total groundwater volume, depending on the morphodynamic influences and the amount of recharge the delta receives. Results show that deltas located in dry climates are most susceptible to salinity and that wave or fluvial delta are especially susceptible. The generic groundwater models of the three delta types are used to understand the vulnerability of 55 real deltas to groundwater salinization through lateral saltwater intrusion. The result of this research provides an initial estimate of the amount of freshwater within deltas, identifies where salinity is most likely to occur within a delta, and suggests which delta types are most vulnerable to groundwater degradation.

The Risk of Tsunamis to Coastal Groundwater Resources in Northern Cascadia (MSc, Bartlett, in progress). Tsunami inundation poses a threat to human society—not only through damage to infrastructure along coastlines, but also through the salinization of groundwater-bearing geologic formations known as aquifers. This study focuses on the most recent and well-preserved far-field tsunami in Northern Cascadia – the 1964 Alaska tsunami, which was known to have impacted both locations. Using sedimentological and groundwater modeling techniques, a framework for assessing the risk of groundwater contamination resulting from tsunami inundation will be developed.

Groundwater Drought: Developing Quantitative Indicators and Mapping Drought Susceptible Aquifer - Stream Systems in British Columbia (MSc, Gullacher, 2022). Aquifers in mountainous regions can be susceptible to periods of drought, but the aquifer response to drought is complex due to groundwater – surface water interactions. In this study, early season and drought season core indicators of groundwater drought are derived from groundwater level, streamflow and climate data. The indicators are informed by the response mechanism of the aquifer-stream system, with two end-members: recharge-driven or streamflow-driven. Generalized additive models are used to determine which combinations of predictor variables for specific regions in British Columbia are associated with summer groundwater levels. Additionally, the Standardized Groundwater Level Index is used to identify wells that had pronounced responses to drought. Drought susceptibility mapping of aquifers in the Okanagan Basin was completed using aquifer hydraulic diffusivity and well density. The classification identified five aquifers that are highly susceptible to drought. The combination of indicators and the aquifer drought susceptibility map can be used for drought-related decision-making in British Columbia.

Evaluating the Feasibility of using Artificial Neural Networks to Predict Hydrogeologic Units in Complex Glacial Deposits (MSc, Hammond, 2022). The feasibility of using Multilayer Perceptron (MLP) to predict hydrogeologic units (HGUs) in complex glacial deposits is evaluated. The study area includes the Fraser-Whatcom Basin. Material descriptions from boreholes logs are standardized into HGUs using natural language processing techniques to reduce subjectively and improve automation. Three data selection alternatives are considered to evaluate the training and prediction capabilities of MLP. Block-model representations of the subsurface are created and the best geologic realization is verified against predictions using the K-nearest neighbours algorithm and geologic cross-sections from independent studies. Validation results show MLP predictions are typically more generalized but produce similar subsurface trends and can recreate confining units contributing to local artesian conditions. MLP appears to be a promising algorithm to solve multi-class classification for geologic modelling purposes. The workflow developed has the added benefit of being stochastic with the potential to generate multiple geologic realizations to account for uncertainty in geologic structure.

Mapping the Likelihood of Flowing Artesian Conditions in the Okanagan Basin and Lower Fraser Valley, British Columbia (MSc, Johnson, 2021) Drilling into an aquifer that exists under flowing artesian conditions can have significant environmental and socio-economic consequences. Unfortunately, the risk of drilling a flowing well in different regions of British Columbia is largely unknown. This study used Multi-Criteria Analysis and the Analytical Hierarchy Process to map the likelihood of flowing well occurrence in three hydrogeologic contexts based on aquifer type and location; 1) Okanagan Bedrock, 2) Okanagan Unconsolidated and 3) Fraser Valley Unconsolidated. A novel approach was used to determine the weights of each factor by using the Wilcoxon Rank Sum Test. Each map was determined to reasonably display and predict the extent of flowing artesian conditions by using the Wilcoxon Rank Sum Test to a significance level of 15%. Through site specific evaluations, Well Drilling Advisories are recommended to be developed by the Province for Naramata, Armstrong, and Aquifer 33 in Langley to alert drillers of flowing artesian conditions.

Shale Gas Development Impacts on Water Resources. For the past several years we have been conducting hydrogeological and hydrogeochemical studies in Northeast British Columbia to assess various impacts of shale gas development on water resources (see student projects below). Shale Gas Development in NE BC was used as a case study area for evaluating risk and resilience in the context of the Water-Energy-Food Nexus. This part of the research was funded in part by the Research Institute for Humanity and Nature (Kyoto, Japan) as part of a larger circum-Pacific project on nexus issues, and the. The research has been carried out in partnership with the BC Ministry of Forests, Lands and Natural Resources, BC Ministry of Environment, Geoscience BC, the BC Oil and Gas Commission, the School for Public Policy at ¶¡ÏãÔ°AV (among others).

Characterizing the Baseline Hydrogeochemistry of a Shallow Groundwater System in the Peace Region, Northeast British Columbia (MSc, Martinolich, 2022) In most areas that support resource development, the natural/baseline groundwater quality is poorly understood, limiting our ability to assess groundwater quality impacts. This research utilizes an integrated multivariate statistical – numerical hydrogeochemical modeling approach to characterize the baseline hydrochemistry of a shallow groundwater system in the Peace Region, northeast British Columbia, where oil and gas development has raised concerns for groundwater quality. K-means clustering was used to define water types and construct hydrochemical maps, hydrogeochemical modeling was used to simulate the hydrogeochemical evolution of the groundwater, and radiocarbon/tritium dating provided groundwater residence times. In unconsolidated aquifers, carbonate mineral dissolution driven by CO₂/CH₄ flux produces Ca-HCO₃ and Ca-Mg-HCO₃ groundwater that often exhibits elevated sulphate and sodium due to mixing. Outside of paleovalleys, the groundwater is typically <60 years old. In the bedrock, cation exchange, and carbonate, gypsum, and silicate mineral dissolution driven by CO₂/CH₄ flux produce mixed-HCO₃-SO_­4 and Na-HCO₃ groundwater. The groundwater is typically >8,000 years old.

Geochemical Compositions of Subsurface Materials and the Potential Impacts on Groundwater Quality from Fugitive Methane within the Peace Region, British Columbia (MSc, Allen, A., 2021) Methane accumulation in groundwater from gas migration induced by hydrocarbon extraction can lead to degradation of water quality. This research focuses on the potential impact elevated concentrations of methane can have on shallow groundwater systems based on the geochemical properties of the sediments and rocks that are present. Bulk chemical characterization of major oxides, trace elements, and rare earth elements indicate that lithologically similar geologic materials in the Peace Region of British Columbia share some geochemical similarities at a regional scale. Investigation of hydrogeochemical characteristics through sequential extraction experiments suggests there is little difference between materials regarding their potential for mobilization of trace elements into groundwater. PHREEQCi numerical models of methane interacting with these materials indicate there is a greater impact in reducing compared to oxidizing conditions, and the presence of carbonate and iron oxyhydroxide minerals mediate the influence large fluxes of methane have on the hydrochemistry.

Characterizing the Contamination Risk in the Surface/Shallow Subsurface Zone due to Wastewater Spills and Leaks from Shale Gas Activities (MSc, Rosales-Ramirez, 2020). The study area is the Peace River Region in northeastern British Columbia where shale gas activities are rapidly expanding. Numerical models (TOUGH2) are being developed to define the extent of the contamination footprint, as well as to determine the rate of transport and fate of the wastewater in case of accidental release.  The results will be integrated into the shallow groundwater intrinsic vulnerability map (above) to evaluate and quantify the risk from these events in an effort to define areas with low-high risk response to wastewater spills or leakages. The resulting maps can be used in decision making to reduce the risk of potential water contamination, as well to raise awareness and promote better monitoring practices.

Investigating the Role of Buried Valley Aquifer Systems in the Regional Hydrogeology of the Peace River Region of Northeast British Columbia (MSc, Morgan, 2018). Geological and numerical flow models were developed to explore the hydraulic role of buried valley aquifers in regional groundwater flow and assess the potential groundwater resource. The study area was the central Peace Region in Northeast British Columbia. The reservoir software Petrel was used to construct the geological model of a buried valley network by integrating interpretations from an airborne electromagnetic survey (SkyTEM) and borehole gamma-ray and lithology logs. This detailed geological model and a simplified geological model were used to develop two numerical flow models in MODFLOW. The modelling results suggest that permeable deposits exist within the buried valleys, but are not regionally connected throughout the whole network, and thus do not play a significant role in the regional groundwater flow regime. However, extensive permeable deposits within the buried valleys appear to exist at smaller scales, and may offer a viable water source in the area.

Numerical Modeling of Deep-Aquifer Wastewater Disposal in Northeast British Columbia (MSc, Simons, 2018). Dense, saline wastewater generated during oil and gas activities (hydraulic fracturing and production) is commonly disposed of in deep formations, but the migration of this wastewater after entering the subsurface is poorly understood. This study uses numerical models to simulate wastewater disposal in the Paddy-Cadotte of Northeast British Columbia using both single-well axisymmetric box models and a regional model of the formation in which multiple disposal and water source wells operate. A sensitivity analysis performed on the box models reveals that dispersivity and permeability exert the strongest control on overall wastewater distribution. Models show that wastewater migrates further than predicted using a simple volumetric calculation, and extends further along the base of the formation than the top due to variations in fluid density. Interference between disposal and source wells is observed to influence wastewater migration, while formation dip and regional groundwater flow have no discernible impact.

Springs in Northeast British Columbia (Bystron, MSc, 2018) Springs in the Peace River Regional District are important fresh water sources for domestic and industrial use, however, little is known about their hydrogeology. This study investigated the controls on spring occurrence and delineated the spring source areas (SSA). Samples from 36 springs were collected and analyzed for chemical and isotopic composition. The chemistry suggested 20 Quaternary and 16 Bedrock aquifer sourced springs. A GIS-based multi-criteria decision analysis integrated spring-related factors (slope, curvature, hydrogeological features, topographic wetness index, surficial geology, and drift thickness) to produce maps showing the likelihood for occurrence of Quaternary or Bedrock-sourced springs. There was a ~70% success rate for correctly identifying sources of the sampled springs. A GIS-based tool was applied to determine topographic SSA’s for 33 springs with varying degrees of success. Although both the maps and SSAs contain uncertainty, there is sufficient information to support decision-making in water resource protection and management.

Investigating Regional Groundwater Flow Influences on Slope Stability in Unlithified Materials (MSc, Dandurand, 2018). Elevated pore pressures play an integral part in slope failure; however, the nature of the regional groundwater flow regime is often not incorporated in slope stability analysis. This research aims to improve our understanding of how the dynamic nature of the groundwater flow regime exerts control on the regional occurrence of landslides in unlithified materials. An integrated hydrogeological – geotechnical methodology is used to investigate the hydrogeological controls on slope stability in Northeast British Columbia. A two-part approach utilized both a series of steady-state groundwater models developed using SVFLUX to investigate the role of geologic contact geometry and hydrogeological characteristics, and a transient groundwater model developed using MIKE SHE to investigate the role of climate. The analysis of these groundwater results highlights implications of regional and local scale hydrogeological processes on pore water pressures. Several challenges were encountered in regard to investigating processes at fine scale resolution within in a large scale groundwater flow model, and an inability to export unsaturated zone results from MIKE SHE limited the slope stability modeling in SV SLOPE.

Shallow Groundwater Intrinsic Vulnerability Mapping for North East British Columbia (Post-Doctoral Fellow, Holding, 2015) ¶¡ÏãÔ°AV (¶¡ÏãÔ°AV), with financial support from the BC Ministry of Forests, Lands and Natural Resource Operations (FLNRO) and the Pacific Institute for Climate Solutions (PICS), developed a Shallow Groundwater Intrinsic Vulnerability Map of Northeast British Columbia (BC).  The assessment was conducted in response to mounting concerns surrounding water management and protection in Northeast BC in relation to shale gas development. The intent of the mapping is to characterise the intrinsic vulnerability of near surface geological materials to contamination originating at land surface. The resulting map is intended to support agencies in the development of policies and regulations that protect groundwater quality.

Aquifer-Stream Hydraulic Connectivity

Groundwater - Surface Water Exchange Dynamics in Low- Gradient and Tidally Influenced Streams in the Lower Fraser Valley (PhD, Mitton, in progress) The study aims to build an understanding of groundwater-surface water exchanges in tidally influenced and low-gradient stream systems, and how hydrogeological and hydrological processes interact to drive hydrological variability. A main goal is to link aquifer and stream dynamics mechanistically to environmental response metrics (e.g., hydraulic-habitat, geochemical, and biological variables) to support management decisions related to the evaluation of potential impacts of hydrological alteration (e.g., groundwater pumping) and the determination of environmental flow needs (EFNs) in groundwater dependent, low- gradient, and tidally influenced streams.

Investigating the Moderating Effects of Groundwater Discharge and Mountain Headwaters on the Thermal Regime of a Stream During Summer Low Flow Conditions (MSc, Antesz, in progress). Stream temperature is influenced by many processes, including atmospheric conditions and water contributions from various sources. This study investigates the moderating effects of groundwater discharge and mountain headwaters on the thermal regime of a stream during summer low flow conditions. The spatial and temporal variability of stream temperature are being measured using a combination of in-situ stream temperature measurements and thermal remote sensing data, with the stable isotopes of water used to understand source areas.

An Ecological Assessment of Aquifer-Stream Connectivity in a Groundwater Dependent Stream (MSc, Mitton, 2021) The ecological roles of groundwater are rarely properly addressed in water management due to a lack of understanding of the mechanisms influencing river ecosystems and inadequate methods to assess potential impacts of activities like groundwater pumping. Here, a hydroecological field study was undertaken in Bertrand Creek, South Coast region of British Columbia, to characterize aquifer-stream exchanges, their drivers, how they influence aquatic habitat and macroinvertebrates, and to develop a method to assess potential groundwater pumping impacts. Data collected from May to October from 2018 to 2020 showed declining groundwater levels in response to hotter and drier conditions, but groundwater discharge was sufficient for streamflow to persist downstream. In 2020, groundwater cooled the stream and maintained habitat conditions that allowed macroinvertebrates to survive the summer. Habitat models built with these data were integrated with an analytical streamflow depletion model to produce a tool for assessing the ecological impacts of groundwater pumping.

Quantifying Aquifer-Stream Exchanges Along Bertrand Creek, British Columbia and Washington State, Using a Numerical Groundwater Flow Model (BSc USRA project, Nott, 2020) The purpose of this study was to quantify aquifer-stream exchanges along Bertrand Creek, in order to identify reaches where streamflow drought may occur. A steady-state three-dimensional numerical groundwater flow model of the watershed was developed. See Research Highlights for a link to the report.

Aquifer-Stream Connectivity at Otter Park, Langley, BC (BSc Honours, Johnson, 2018) Streams that are hydraulically connected to an aquifer can be adversely impacted by groundwater abstraction, which may result in streamflow depletion.  Characterisation of the potential for streamflow depletion is thus an important aspect of water management. The purpose of this study is to characterise the aquifer and streambed sediment properties at Otter Park in Langley, British Columbia, in order to evaluate streamflow depletion due to pumping. The aquifer and streambed sediment properties were characterised through a series of methods, including grain size analysis, slug and bail tests, and a 30 hour pumping test. Streambed sediments have a hydraulic conductivity approximately one order of magnitude lower than the aquifer sediments. Hydraulic connectivity between the aquifer and the stream was assessed using stream discharge, vertical hydraulic gradients in nested instream piezometers, and streambed temperature. Several lines of evidence indicate that streamflow depletion occurred; however, the variation in the streamflow data limits the conclusions that can made without a longer pumping test. 

Investigating the Thermo-Hydraulic Regime of Union Creek, Langley BC (BSc Honours, Whistler, 2018) Groundwater abstraction near a stream can impact the surface water by changing the direction and magnitude of the groundwater flux and the thermal regime of the stream. In this study, a thermo-hydraulic survey was conducted at Steele Park, Langley B.C, to assess the thermal and hydraulic regime of Union Creek through the summer season and under non-pumping and pumping conditions. Groundwater flux measurements across the streambed and cross-correlation analyses between streambed temperature and air temperature, show Union Creek to be primarily a losing stream. The temperature signals recorded at the streambed at upstream locations lagged behind  those downstream due to a more immediate response to radiative heating in shallower waters downstream. From non-pumping to pumping, streambed temperatures and stream stage did not change, and unfortunately, the vertical flux results were uncertain. Thermal infrared images did not show groundwater discharge into the stream, but suggest seepage of warm water from the bank storage during summer. Analysis and interpretation show the significance of properly characterizing hydraulic properties to investigate the hydraulic connectivity with confidence.

Investigation of Aquifer-Stream Connectivity at Steele Park, Langley BC (BSc Honours, Hall, 2017) Abstraction of groundwater from a pumping well located beside a stream can result in sourcing of the pumped water directly from the stream and consequent depletion of stream discharge. The ability to accurately estimate stream depletion due to pumping is necessary for water rights management. A 48-hour pumping test was conducted at Steele Park, Langley BC to assess aquifer-stream connectivity and the effects of pumping on streamflow and groundwater seepage. The site was also modeled using a suite of available analytical solutions for streamflow depletion. Analysis of the field data highlighted the importance of accurately characterizing the hydraulic properties of the streambed sediments and properly designing and implementing the field test. Techniques for measuring field parameters crucial for direct comparison between field data and the analytical streamflow depletion models are discussed.

Hydrogeochemistry

Bonding environment and distribution of arsenic and selenium in pyrite and controls on element mobilization. (PhD, J. Ross-Lindeman, in progress) is investigating the reaction mechanisms of arsenic and selenium oxidation and mobilization during arsenic- and selenium-rich pyrite oxidation, a process that can potentially introduce contaminants to surface water and groundwater. This research combines chemical and mineralogical characterization of arsenic and selenium in pyrites, including trace element concentration, speciation, and distribution, with experiments on pyrites to understand the effects of arsenic or selenium substitution on oxidation reaction mechanisms.

Investigating the Geochemistry of Selenium in the Residual from Biologically Treated Mine-Impacted Waters (MSc, L. Devolder, 2018) The goal of this study is to determine which selenium species are present in the residual and under what conditions it may become mobile in aqueous phase. Detailed selenium speciation of the residual is being determined using sequential extraction procedures in the laboratory and X-ray Absorption Near Edge Structure analysis at two separate synchrotron facilities.  A series of aqueous geochemical batch experiments that simulate different redox and pH conditions are being used to determine under what conditions the selenium may mobilize and if certain species are more vulnerable than others. This study aims to help quantify the risk posed by the residual and eventually develop safe disposal methods. 

Sources and Distribution of Arsenic in Groundwater on the Gulf Islands of British Columbia (BSc Honours, A. Allen, 2018). Arsenic mobilization to groundwater results in significant impacts on groundwater quality which can lead to adverse health effects. Understanding in what form the arsenic occurs is critical to determining the potential for arsenic contamination. Mineralogical and bulk chemical analyses, a cation exchange capacity experiment, and a chemical sequential extraction procedure for arsenic speciation were performed to determine the abundance and occurrence of arsenic in rocks from several formations of the Nanaimo Group in the Gulf Islands of British Columbia. Through these methods it was found that arsenic is strongly associated with iron oxides, oxyhydroxides, and sulfides. Results indicate finer grained formations have higher arsenic content, and a minor correlation exists between formations which contain elevated arsenic in groundwater and higher abundances of more easily mobilized arsenic.