If a liner is required to meet the standards set forth in WAC 16-201-028, then it must be constructed as follows:

(1) Synthetic liners:

(a) Synthetic liners shall be chemically compatible with the materials being stored within the permanent storage facility and have a minimum thickness of thirty mils +/-1 mil. A written confirmation of compatibility and a written estimate of the life of the liner from the manufacturer shall be kept on file at the permanent storage facility or the nearest local office from which the permanent storage facility is administered.

(b) Synthetic liners shall be installed under the supervision of a qualified representative of the manufacturer, a contractor certified by the manufacturer, or a certified engineer. All field constructed seams shall be tested, and repaired if necessary, in accordance with the manufacturer's recommendations.

(2) Permanent storage facilities with storage containers of one hundred thousand gallons or greater may use clay soil liners: Provided, That:

(a) The surface soil shall be sealed, including the berm of an earthen dike, with a sealing agent such as sodium bentonite, attapulgite or a similar clay material[;]

(b) The liner shall be constructed in accordance with reliable civil engineering practices, to achieve a coefficient of permeability not to exceed 1x10-6 cm/sec and shall be maintained at 1x10-5 cm/sec with a thickness of not less than six inches[.][;]

(c) The floor and internal walls of the containment area shall have a protective barrier to prevent desiccation, evaporation, freeze, thaw, or other physical damage.