Occurrence, Origin, and Fate of Redox-Sensitive Constituents in Groundwater in Alberta
Creators: name: Plata Enriquez, Isabel Cristina
Publisher: name: Science
Year: 2024
Subjects: subject: Groundwater
subject: Contaminants
subject: Nitrate
subject: Arsenic
subject: Manganese
subject: Selenium
subject: Geochemistry
subject: FOS: Earth and related environmental sciences

description: The intensification of droughts in Alberta presents growing challenges, particularly regarding the availability of high-quality freshwater for various uses across the province. With surface water sources frequently affected by drought conditions, the reliance on groundwater becomes increasingly crucial to fulfilling essential needs such as drinking and domestic usage. However, an increasing reliance on groundwater underscores the importance of understanding and managing groundwater quality, particularly in light of potential contamination risks from agricultural activities, urban development, and natural geogenic influences. This thesis focused on the occurrence, distribution, potential sources, and fate of contaminants of health relevance, including nitrate (NO3), at a regional scale, while selenium (Se), manganese (Mn), arsenic (As), and iron (Fe) were evaluated at the provincial scale in groundwater in Alberta, Canada. A comprehensive groundwater quality dataset composed of chemical analyses of over 131,000 groundwater samples collected from wells completed in bedrock and surficial sediments from landowner and monitoring wells at depths commonly shallower than 250 m across Alberta provided the base for this study. For each redox-sensitive parameter, a subset of data was selected based on the availability of water quality data because some of the parameters, such as Mn, As, and Se, are not routinely analyzed. The analysis of the available data, including samples below detection limits, indicated that 10%, 22%, and 16% of the groundwater samples exceeded the Canadian drinking water guidelines for NO3, Mn, and As, respectively. In contrast, 1% of the samples exceeded the Canadian drinking water guideline for Se. Elevated concentrations of NO3, Mn, and Fe in groundwater were associated with Ca(Mg)-HCO3 and mix cation-HCO3 hydrochemical facies. In contrast, lower concentrations were noted in more geochemically evolved Na-HCO3 and Na-Cl water types, particularly in groundwater from surficial sediments. Arsenic displayed a more complex distribution, with elevated concentrations observed across various water types in groundwater from surficial sediments and bedrock associated with coal. In contrast, elevated dissolved selenium concentrations were primarily associated with the more chemically evolved Na-HCO3 and Na-Cl water types and groundwater from marine bedrock. Primary sources of dissolved Mn, As, Fe, and Se are geogenic, while elevated NO3 concentrations result from agricultural activities, particularly the application of synthetic fertilizers and manure, in part due to the management of livestock through CFOs in southern Alberta. This study identifies areas more susceptible to groundwater containing elevated concentrations of these potential contaminants that may not be suitable or require pre-treatments before groundwater can be used for drinking.