(a) Individual tanks or groups of tanks, where deemed necessary by the Commissioner on account of proximity to waterways, character of topography, or nearness to structures of high value, or to places of habitation or assembly, shall be diked or the yard shall be provided with a curb or other suitable means taken to prevent the spread of liquid onto other property or waterways. Where a dike enclosure is required under this section, it shall have a net capacity not less than that of the largest tank, plus 10 percent of the aggregate capacity of all other tanks served by the enclosure.
Dike construction
(b) Except where protection is provided by natural topography, dikes or retaining walls required under the foregoing section shall be of earth, concrete or solid masonry designed to be liquid tight and to withstand a full hydraulic head, and so constructed as to provide the required protection. Earthen dikes 3 feet or more in height shall have a flat section at the top not less than 2 feet wide. The slope shall be consistent with the angle of repose of the material of which the dikes are constructed.
Drainage
(c) Where provision is made for draining rain water from diked areas, such drains shall normally be kept closed and shall be so designed that when in use, they will not permit flammable liquids to enter natural watercourses, public sewers, or public drains, if their presence would constitute a hazard.