(a) In this section, “secondary containment” means a method by which a secondary wall or barrier is installed around an underground storage tank system in a manner designed to prevent a release of a regulated substance from migrating beyond the secondary wall or barrier before the release can be detected. A secondary containment system may include an impervious liner or vault surrounding a primary tank or piping system or a double-wall tank or piping system.
(b) An underground storage tank system, at a minimum, shall incorporate a method for secondary containment if the system is located in:
(1) the outcrop of a major aquifer composed of limestone and associated carbonate rocks of Cretaceous age or older; and
(2) a county that:
(A) has a population of at least 1.2 million and relies on groundwater for at least 75 percent of the county’s water supply; or
(B) has a population of at least 75,000 and is adjacent to a county described by Paragraph (A).

(c) § 26.3475(e) applies to an underground storage tank system that is subject to this section as if a violation of this section were a violation of § 26.3475.
(d) Notwithstanding § 26.359(b), a political subdivision under this section may adopt standards for the containment of underground storage tank systems.