(a) Except as otherwise provided in subdivision (b), “existing hazardous waste facility” means a Class I disposal site, as defined in Section 2510 of Title 23 of the California Administrative Code on the effective date of this article, and which, in addition, is either:

1. (1) A facility operating as of May 1, 1981, pursuant to a valid hazardous waste facility permit issued by the department pursuant to Section 25200.
2. (2) A facility operating as of May 1, 1981, pursuant to a grant of interim status by the department pursuant to Section 25200.5.