Groundwater contaminated by leachate from historic landfills, closed and typically without liners or leachate-collection systems, can potentially discharge to surrounding surface waters and impair their ecological communities. However, few studies have focused on emerging contaminants (e.g., per- and poly-fluoroalkyl substances (PFAS)), inputs to non-flowing water bodies, and exposure across the various ecological zones. The objective of this study was to better understand the ecological risk posed by a historic landfill plume discharging to a nearby pond, and how the pond’s ecosystem may be affected by potential spatio-temporal variability in contaminant concentrations and contaminant discharge. The site contained an artificial pond 40m west of a historic sanitation landfill and was monitored for ~1 year. Seasonal samples of shallow groundwater analyzed for standard chemistry plus artificial sweeteners and PFAS revealed a large and seasonally stable plume footprint in the pond and relatively constant exposure to the endobenthic zone (within sediments), with some constituents at potentially toxic concentrations. Elevated electrical conductivity measured just above (~1 cm) the sediment bed indicated exposure to the epibenthic zone, with greater exposure associated with higher groundwater fluxes at night, after rain and melt events, and in winter. It is speculated that terrestrial evapotranspiration and pond evaporation play a role in these temporal patterns. Estimated contaminant mass fluxes into the pond using contaminant and temperature-based flux data showed spatial variability within the plume footprint and seasonal patterns. Concentrations in the pond water showed exposure to pelagic organisms was consistent for chloride and saccharin (and likely PFAS), but varied seasonally for nitrate and ammonium, with all at lower concentrations compared to the endobenthic and epibenthic zones. This study revealed significant and variable ecological exposure from a landfill leachate plume discharging to a pond and provides guidance to landfill operators on improved monitoring protocols for such sites. / Thesis / Master of Science (MSc) / Groundwater contaminated by historic landfills, closed and typically without liners or leachate-collection systems, can potentially discharge to surrounding surface waters, threatening their ecological communities. The objective of this study was to better understand the ecological risk posed by a historic landfill plume discharging to a nearby pond, and how this might vary spatially and temporally. The study site contained an artificial pond 40m west of a historic sanitation landfill and was monitored for contaminant concentrations and contaminant discharge for ~1 year. Elevated concentrations of leachate contaminants were relatively steady within the sediments (endobenthic zone) and similar across the contaminant discharge area but varied substantially in space and time (higher at night, after events, in the winter) at the pond bed (epibenthic zone), while the patterns differed by contaminant in the surface water above (pelagic zone). These findings can provide insights into improved monitoring and protection of ecosystems at landfill sites.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/26320 |
| Date | January 2021 |
| Creators | Hua, Tammy |
| Contributors | Smith, James, Roy, James, Earth and Environmental Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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