(1) Prefabricated [secondary containment] shall be composed of a rigid prefabricated basin having both a base and walls constructed of steel or synthetic materials which are resistant to corrosion, puncture or cracking. Materials used in the secondary containment shall be chemically compatible with the products being stored within the secondary containment. A written confirmation of compatibility from the basin manufacturer shall be kept on file at the permanent storage facility or at the nearest local office from which the permanent storage facility is administered.

(2) The prefabricated secondary containment shall be designed and installed to withstand all foreseeable loading conditions, including the tank load and a full hydrostatic head of any discharged liquid. Multiple basins connected to provide the capacity required in WAC 16-201-025 shall be connected in a manner which assures an adequate transfer of discharged liquid between basins.