Drums containing regulated substances (listed in 40 CFR §68.130) are stored in several separate locations at a stationary source and there is no possibility that an accidental release in any of the individual storage areas would impact any of the other storage areas. Must the overall amount of the regulated substance present at the stationary source be considered when determining whether the threshold quantity for that substance is exceeded?

No. Applicability of the risk management program regulations at 40 CFR Part 68 is contingent upon the existence of more than a threshold quantity of a regulated substance in a process at a stationary source (40 CFR Section 68.10(a)). Although the definition of "process" does include storage, the total amount of a regulated substance in storage at a stationary source does not necessarily constitute a single process. Separate, individual vessels must be considered as a single process for the purpose of threshold determination if both could be released during a single release event, including an event that is external to both vessels (40 CFR Section 68.3).

The owner or operator of a stationary source must use his or her best judgment, backed up by a sound technical and scientific basis, to make a determination as to whether two or more vessels may be involved in the same accident, or whether a release from one vessel may reasonably be anticipated to lead to a release from another vessel. The owner or operator should be able to document the decision that the individual vessels do or do not constitute a single process.