(a) Secondary containment for tanks must include one or more of the following:

(1) A liner (external to the tank).

(2) A double-walled tank.

(3) An equivalent device; you must maintain documentation of equivalency at the facility.

(b) External liner systems must be:

(1) Designed or operated to contain 100 percent of the capacity of the largest tank within its boundary.

(2) Designed or operated to prevent run-on or infiltration of precipitation into the secondary containment system unless the collection system has sufficient excess capacity to contain run-on or infiltration. The additional capacity must be sufficient to contain precipitation from a 25-year, 24-hour rainfall event.

(3) Free of cracks or gaps.

(4) Designed and installed to surround the tank completely and to cover all surrounding earth likely to come into contact with the waste if the waste is released from the tank(s) (that is, capable of preventing lateral as well as vertical migration of the waste).

(c) Double-walled tanks must be:

(1) Designed as an integral structure (that is, an inner tank completely enveloped within an outer shell) so that any release from the inner tank is contained by the outer shell.

(2) Protected, if constructed of metal, from both corrosion of the primary tank interior and of the external surface of the outer shell.

(3) Provided with a built-in continuous leak detection system capable of detecting a release within 24 hours.