Difference between an SPCC Tier I and Tier II qualified facility

In the SPCC regulations in 40 CFR Part 112, what is the difference between a Tier I and Tier II qualified facility? How did EPA establish the multi-tiered approach for qualified facilities?

A Tier II qualified facility is one that has an aggregate aboveground oil storage capacity of 10,000 U.S. gallons or less and meets the oil discharge history criteria in §112.3(g)(2). To qualify as a Tier I qualified facility, in addition to meeting the eligibility criteria for a Tier II qualified facility, a facility must have no individual aboveground oil storage containers with a capacity greater than 5,000 U.S. gallons (§112.3(g)(1)). The owner or operator of either a Tier I or Tier II qualified facility may self-certify the facility's SPCC Plan, as provided in §112.6. The owner or operator of a Tier I qualified facility also has the option to complete and implement a streamlined, self-certified SPCC Plan template available in Part 112, Appendix G. The template does not include certain requirements that are inapplicable or unnecessary, and Tier I qualified facilities are subject to streamlined requirements for failure analysis, bulk storage secondary containment, and overfill prevention (§112.6(a)(3)).

EPA established and modified the multi-tiered approach through three separate rulemakings. On December 26, 2006, EPA finalized an amendment to the SPCC Rule to allow the owner or operator of a qualified facility to self-certify his SPCC Plan (71 FR 77266). EPA did not adopt a multi-tiered approach at that time, but did indicate that it intended to explore the approach. On December 5, 2008 (73 FR 72436), EPA designated a subset of qualified facilities as Tier I qualified facilities and established the additional criterion for an individual oil storage container. On November 13, 2009, EPA published technical corrections to the Tier I qualified facility provisions and the Part 112, Appendix G template (74 FR 58784).