40 CFR 165.83: Definition of new and existing structures.

(a) What is a new containment structure? A new containment structure is one whose installation began after November 16, 2006. Installation is considered to have begun if:

(1) You, as the owner or operator, have obtained all Federal, State, and local approvals or permits necessary to begin physical construction of the containment structure; AND

(2) You have either begun a continuous on-site physical construction or installation program OR you have entered into contractual obligations. The contract must be such that it cannot be canceled or modified without substantial loss, and must be for the physical construction or installation of the containment structure within a specific and reasonable time frame.

(b) What is an existing containment structure? An existing containment structure is defined as one whose installation began on or before November 16, 2006.