Groundwater Model Validation of Water-Covered Tailings Facilities at a Closed Uranium Mine
Date
2025-04-23
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0009-4176-3593
Type
Thesis
Degree Level
Masters
Abstract
Closure strategies for metal mines must consider the long-term performance of waste materials
such as tailings. Mine tailings have associated physical and geochemical risks that must be
managed throughout the mine’s life cycle, including the closure period. Acid rock drainage (ARD)
is a common geochemical risk for metal mines that is often managed with the use of a water cover.
Historically, many mines have chosen to manage tailings as a slurry deposited behind containment
dams with a water cover, but this solution comes with physical risks in terms of dam stability. A
careful balancing of physical and geochemical risks must be made when selecting a preferred
decommissioning strategy.
This research considers a closed uranium mine site, the Denison mine, in Elliot Lake, Ontario.
The Denison mine operated with two tailings surface impoundments (TMA-1 and TMA-2)
surrounded by containment dams. The closure of TMA-1 and TMA-2 required a careful balancing
of physical and geochemical risks to select a preferred decommissioning strategy. As a uranium
mine, the management of long-lived radionuclides was also considered in closure planning. The
Denison mine was ultimately closed by stabilizing the perimeter dams and establishing a water
cover over the tailings. The Denison mine provides a useful case study of a water covered tailings
site, with nearly 30 years of post-closure data. The purpose of this study is to examine the
hydrogeological and geochemical performance of the Denison mine with respect to predictions
made in the closure planning stage.
The post-closure monitoring data from the Denison site was used to conduct a validation of
the predicted groundwater seepage rates, groundwater flowpaths, source terms, and performance
with respect to ARD. A numerical groundwater model was developed to determine groundwater
seepage rates and flowpaths, and a preliminary contaminant transport analysis was completed
using groundwater model outputs and an updated source term calculation. Mass flux calculations
are made from the TMAs to receiving water bodies based on seepage rates and flowpaths from a
numerical model. The results serve as a foundation to support future post-closure studies.
Recommendations to refine the modelling going forward were developed.
Description
Keywords
Groundwater modelling, water-covered tailings, mine closure, uranium
Citation
Degree
Master of Science (M.Sc.)
Department
Civil and Geological Engineering
Program
Civil Engineering