Should tank capacity be considered when determining thresholds?

When determining whether a threshold amount of a regulated substance is present in a process (e.g., a tank), must the owner or operator of a stationary source consider the total capacity of the process, or the actual amount of regulated substance contained in the process?

The threshold determination is based on the maximum actual amount of the regulated substance contained in a process at any one time (40 CFR §68.115; see also 58 FR 5102, 5114 (January 19, 1993)).