The interrelationship of material toxicity, stream properties and quantity of spilled material in assessing the risk of hazardous material spills

The current status of regulatory efforts for the bulk carriage of oil and hazardous materials is reviewed. The hazard posed to water resources is examined using the method of risk analysis. A weakness of the present regulatory efforts, namely that aquatic system properties and spill quantity are not considered, is identified. With risk defined as the product of spill probability and severity, a procedure is suggested to better quantify one element of water pollution risk - severity of spill impact. The procedure identifies two major parameters which affect spill impact, concentration of material in the water and the concentration at which the material causes acute toxic effects. Methods are developed to quantify spill concentration in the water, a function of spill size and available dilution water, on a relative scale for use with existing relative toxicity ratings. The combined toxicity and dilution capacity ratings provide a significantly improved measure of water pollution impact, and thus risk. The waterway relative dilution capacity quantification procedures is based on median discharge and considers the effects of longitudinal dispersion and the dynamics of fish mortality. The procedure is applied to the majority of the major inland and intracoastal waterways. Results are expressed as relative dilution capacity ratings for major waterways areas.