Primary storage of bulk liquid pesticides at a permanent storage facility shall be located within secondary containment designed to prevent the release of discharged pesticides. Secondary containment shall consist of:

(1) A wall and liner with a sloped floor as provided in WAC 16-229-030 and 16-229-040; or

(2) A prefabricated facility as provided in WAC 16-229-050.

(3) Secondary containment in operation prior to March 1, 1994, which does not have sloped floors shall be exempt from this section: Provided, That upon alteration to the secondary containment or increase of storage volume, the secondary containment shall be brought into full compliance with this section.