Development of a procedure to use relative spill dilution capacity to manage water pollution risk from the transportation of oil and hazardous materials

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, no consideration of widely varying risk levels, 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 the 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 procedure 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 waterway areas