As of 1993, pure NaCl was generally used in its pure form on main urban roads, highways, and freeways in Metropolitan Toronto. It is by far the least expensive and most effective de-icing agent. On side streets and gravel roads it is used in a condensed, 5% NaCl form along with sand because it tends to damage these roads to a greater extent. Actually, CaCl2 , or calcium chloride, is more effective in below freezing temperatures of -12 to -340 C. The main problem is that it is much more expensive and also makes surfaces slippery when wet (Hanley, 1979).
Salt in ground water not only poses a problem for water consumption, but also industrial application. Several agencies have defined their guidelines of sodium and chloride intake. The Environmental Protection Agency and the Ontario Ministry of the Environment say that a safe concentration of chloride in drinking water is 250 mg/L. Most other agencies agree since people have a taste threshold between 200-300 mg/L. Sodium is a more debated guideline because of the ion's link to the development of hypertension as well as hypernatraemia. A guideline of 200 mg/L is generally accepted for aesthetic purposes only. Some cautious agencies, like European Economic Community, have set their guideline at only 20 mg/L. Regardless, lower concentrations leave less room for worry.
Studies from the late 70s were brought to attention in the mid 80s when Pilon and Howard (1987) measured concentratrions of chloride as high as 14,000 mg/L in pore waters from the unsaturated zone adjacent to highways in Metropolitan Toronto. (GSA TODAY, December, 1993, P301) Although these areas are not used for domestic consumption, it cannot be ignored that these contaminated ground waters flow into a much larger system. With increased pollution, the chloride will spread to urban streams and eventually wreak havoc upon the Great Lakes. This also creates a risk for new developments appearing throughout the Metropolitan Toronto region's watershed.