The development of risk-based spill management criteria related to the beneficial use impairments in the St. Clair River

Spills to the St. Clair River have caused the water treatment plant (WTP) intakes to shut down numerous times. A set of risk-based spill management criteria is developed to evaluate existing and future spill prevention and control measures in the policy planning stage. It estimates the explicit risk of a WTP shutdown due to the violation of the drinking water quality guidelines in a two-year period. The risk is determined by the joint probability of occurrence of the smallest spill chemical event mass and the highest number of WTP shutdown occurrences. Based on the spill data from 1988-1997 and 1998-2007, the risk of WTP shutdown in a two-year period due to benzene spills is 86% and 50%, respectively; and vinyl chloride spills is 17% and 9%, respectively. The study concludes that the risk of WTP shutdown due to spills has been decreasing in the St. Clair River over the past 20 years.