The Materials Transportation Bureau (MTB) and US Environmental Protection Agency (EPA) have agreed to regulate the transportation of hazardous substances only when they are shipped in larger than reportable quantities. This agreement simplifies the transportation regulations associated with hazardous substances and reduces the cost of complying with those regulations. However, it presents a potential risk of multiple small-package spills. A method is developed for assessing this spill risk by using data available from the Hazardous Material Incident Reporting System. Application of the data and methods revealed that the risk from multiple small-package spills was less than 0. 5 percent of the risk of other regulated spills. Thus, the decision by EPA and MTB to regulate the transport of hazardous substances only when shipped in larger than reportable quantities is supported.

Section 311 of the Clean Water Act (CWA, Public Law 95-217) establishes a program for regulating hazardous substances.[CWA amends the Federal Water Pollution Control Act of 1972 (Public Law 92-500).] Pursuant to this legislation, 297 substances were designated as hazardous by the US Environmental Protection Agency (EPA). These 297 substances were categorized into five groups based on their aquatic toxicity, and each group was assigned a reportable quantity (RQ). The groups and associated RQs are as follows: X, 1 lb; A, 10 lb; B, 100 lb; C, 1,000 lb; and D, 5,000 lb.