204. Any underground portion of piping connected to an underground tank installed after 11 July 1991 on a Class A site referred to in the fourth paragraph of section 168 must have a double wall that meets the requirements of the first paragraph of that section. The piping must also be connected at its lowest point to a leak-proof collector well having an automatic leak detection system with a visual and audible alarm that meets the requirements of the second paragraph of that section.