(A) Required. Tanks or groups of tanks shall be protected from the effects of flammable liquid spills originating at or encroaching upon the tank setting.
(B) Methods. Diversion walls or drains safely directing the flow to catchment basins, impounding basins formed by dikes around tanks or groups of tanks, or combinations thereof shall be used.
(C) Capacity. The net capacity of a catchment basin, diked impounding basin, or any combination thereof shall be equal to the capacity of the largest tank, plus six inches of freeboard. In computing the required capacity of a catchment basin, diked impounding basin or combination thereof:
(1) The volume of the largest tank up to the height of the dike shall be considered as part of the available capacity of a diked impounding basin.
(2) No part of the volume of tanks other than the largest tank shall be considered as part of the available capacity.
(3) The capacity of a separate catchment basin may be used to reduce the required capacity of a diked impounding basin provided drainage sufficient to prevent overflow of the dike and effective control of flow are provided.
(4) The capacity of a single separate catchment basin may be applied to reduce the required capacity of each of the diked impounding basins draining to it.
(D) Dike construction, drainage and division. Where dependence is placed in whole or in part on diking for compliance with this subchapter, dikes shall be constructed, drained, and divided as follows:
(1) Construction. Dikes shall be of earth, concrete or solid masonry designed to be liquid-tight to withstand a full hydraulic head, and shall be maintained at full design capacity. Where piping passes through dikes, provision shall be made for movement without damage to the dikes and to minimize leaks under emergency conditions. Earthen dikes shall be built and maintained at a minimum height of two feet. The distance between the inside toe of any dike and the shell of any tank not over 30 feet in diameter shall be not less than five feet, and for tanks over 30 feet in diameter shall be not less than 10 feet.
(2) Spill dikes. Where tanks within a common diked impounding basin may cause mutual exposure from spills, spill dikes shall be provided between tanks of 10,000 barrels or greater individual capacity. Groups of tanks of less than 10,000 barrels individual capacity and not in excess of 15,000 barrels aggregate capacity may be enclosed within a single spill dike. The height of such spill dikes shall not exceed 50% of the height of the main or perimeter dikes.
(3) Drainage. Drainage shall be provided at a consistent slope of not less than one percent away from tanks and fittings toward a sump, drain box or other safe means of disposal located within the diked impounding area and at the greatest possible distance from the shell of the tank. Traps with not less than six inches of liquid seal shall be provided between the sumps, drain boxes or drain openings within the diked area and the sewers or drains intended for disposal of spills. A valve, operable from outside the dike, shall be provided in the dike drain system and shall normally be kept closed.
(4) Disposal. Approved provision shall be made for disposing of water and oil retained by diked impounding basins or catchment basins.
(E) Deviations. In particular installations, deviations from the provisions of this section may be granted by the Building and Safety Inspector, after consideration of special features such as:
(1) Topographical conditions, nature of occupancy and proximity to buildings on the same or adjacent property;
(2) Capacity and construction of proposed tanks and character of liquids to be stored and nature and quantity of private and public fire protection provided.
('81 Code, § 5.40.170) Penalty, see Ch. 13