Surface Preparation for Aboveground Storage Tanks
Aboveground storage tank installations should have specifically designed foundations to ensure adequate support of a full tank and that spillage from filling, transfer and dispensing operations will not create a hazard.
The Alberta Fire Code states that storage tanks shall rest on the ground or on foundations, supports or piling made of concrete, masonry or steel. A professional doing the installation design would have to determine whether or not a foundation will be adequate.The design of the foundation would consider the weight of the tank, the specific gravity of the stored liquid, the surface area in touch with the foundation and the load-bearing capacity of the soil and drainage around the tank.
The primary criterion for tank foundation design is the load-bearing capacity of the soil. This can range from 1,000 lb/ft2 in soft clay, to over 4,000 lb/ft2 in course, compacted gravel. A fully loaded, 50,000L horizontal, double-walled tank can weigh over 100,000 lbs. Depending on the surface area of the footings or support for the tank there can be a great deal of weight on each part of the assembly in contact with the earth. Placing tanks on native soil may not provide sufficient support.
Related to site preparation is the consideration of drainage systems. Transfer of product during tank filling and spillage that occurs when dispensing petroleum requires that grading and sloping is included with a site design. The Alberta Fire Code states that spills shall be prevented from flowing outside the spill area and from reaching waterways, sewer systems and portable water sources by constructing non-combustible barriers capable of containing the spill or grading the site or sloping the floor to divert the spill to a drainage system. Be aware that some municipalities in Alberta require oil/water separators with any construction involging tanks and dispensers. As part of the facility design the engineer must consider loss of product from around the tank (if not in a conventional dike containment) and from remote loading points and around any dispensers connected to the tanks. Like for foundations, native soil would not normally be sufficient to prevent petroleum from getting through the soil to the water table.
The PTMAA requires that submitted applications include evidence that an engineer has given consideration to these Fire Code requirements.