Volume 20, Number 1 (1993)
Articles

Groundwater Contamination Due To Road De-icing Chemicals — Salt Balance Implications

Ken W. F. Howard
Groundwater Research Group, University of Toronto, Scarborough Campus, Scarborough, Ontario.
Janet Haynes
David L Charlesworth and Associates Inc., Toronto, Ontario.

Publié-e 1993-03-03

Comment citer

Howard, K. W. F., & Haynes, J. (1993). Groundwater Contamination Due To Road De-icing Chemicals — Salt Balance Implications. Geoscience Canada, 20(1). Consulté à l’adresse https://journals.lib.unb.ca/index.php/GC/article/view/3784

Résumé

Every year, roads and highways in Metropolitan Toronto receive more than 100,000 tonnes (t) of NaCl road de-icing chemicals. While much of this salt is flushed from the region every winter season by overland flow, a proportion will enter the sub-surface and eventually discharge to urban streams as baseflow. To determine annual retention rates of de-icing salts in an urban watershed, a chloride mass balance has been applied to the Highland Creek basin, a typical urban catchment in eastern Metropolitan Toronto. The catchment has an area of 104 km2 and groundwater recharge is estimated to be 162 mm per year. Chloride in put to the catchment was determined from municipal records. These show that the catchment receives approximately 10,000 t of chloride annually, predominantly in the form of NaCl de-icing chemicals which are applied to road, highways and parking lots during the winter months. Chloride output was estimated from stream flow and electrical conductivity measurements recorded at 15-minute intervals over a two-year period. The balance reveals that only 45% of the salt applied to the catchment is being removed annually and that the remainder is entering temporary storage in shallow sub-surface waters. If present rates of salt application are maintained, it is predicted that average steady-state chloride concentrations in ground waters discharging as springs in the basin will reach an unacceptable 426 ± 50 mg·L-1 possibly within a 20-year time frame. The value of 426 mg·L-1 represents a three-fold increase over present average baseflow concentrations, and is nearly twice the drinking water quality objective of 250 mg·L-1 maximum acceptable concentration.