Assessing the risk of sodium chloride contamination to a potable water source in Waterloo

The City of Waterloo wishes to conduct a feasibility study to determine the risk-level of sodium chloride infiltration to a potable groundwater source within the Laurel Creek subwatershed. The infiltration risk is related to stormwater management facilities (SWMFs) and low impact developments (LIDs). SWMFs and LIDs are used to infiltrate a large portion of stormwater flows and to help reduce peak flows as well as capture suspended solids and contaminants. Despite these positive impacts, SWMFs and LIDs also have the potential to increase the risk of groundwater contamination in well head protection areas from a number of substances, including sodium chloride from road salt. Waterloo plans to evaluate sodium chloride infiltration by assessing scenarios using an integrated surface (CANWET) and groundwater (MODFLOW) modelling approach when retrofitting SWMF and LID features. This approach will be validated through a field-monitoring program. In doing so, the city hopes to demonstrate the potential removal of 80% of total sodium chloride infiltrating groundwater. This project aligns with the regional Grand River Source Protection Plan and the City of Waterloo Stormwater Master Plan. It will help the city preserve a potable water source for the community. Innovative aspect(s): • This project is the first in Canada to combine CANWET surface and MODFLOW groundwater modelling to evaluate stormwater facility retrofitting for the risk of groundwater contamination • This model will also allow for the evaluation of cumulative effects in the watershed decision-making process, rather than assessing proposed changes in isolation Replicability: This project will be completed in partnership with the University of Guelph, who developed the model. The replicability of the findings will be increased through this knowledge-sharing partnership. Many municipalities in Ontario, and across Canada, rely on groundwater for potable water. Testing this model in Waterloo and verifying it through field monitoring will be useful for the many communities that need to preserve potable water sources from sodium chloride contamination. (Project description from original funding application)