2. Storage of liquid petroleum products, except those incidental to the following:
2. Storage of liquid petroleum products, except those incidental to the following: a. Normal household use, outdoor maintenance, or heating of a structure; b. Waste oil retention facilities required by statute, rule or regulation; c. Emergency generators required by statute, rule or regulation; d. Treatment works approved under 314 CMR 5.00 for treatment of ground or surface waters provided that storage listed in items a. through d. above, is in free-standing containers within buildings or above ground -111- with secondary containment adequate to contain a spill the size of the containers total storage capacity; however replacement of existing tanks or systems for the keeping, dispensing or storage of gasoline is allowed consistent with state and local requirements. Other liquid petroleum products may be stored subject to the provisions of Section 5.25.2 (12) hereof.