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IF Annular Pontoon Floating Roof Rather than using cheaper pans or flimsy construction, Chevron uses all welded steel with bulkheaded and compartmented pontoon sections. This ensures that buoyancy is maintained even if several compartments are flooded with product by corrosion holes, cracks or other problems that can occur with floating roof designs. As long as the floating roof is buoyant, the fire danger is drastically reduced. This is why Chevron chooses to use only the best floating roof designs. It should be noted that floating roofs are adopted only for volatile, flammable liquids such as aviation gasoline or motor gasoline, but not for diesel or jet fuels, since these have low emissions at ambient temperatures. Floating Suction While most companies withdraw product directly from the bottom of the tank, the cleanest product is at the surface. Contaminants such as rust, dirt and water settle to the lower levels, so we withdraw only clean product from the top of the tank. The swivel allows the inlet to pivot to the surface, and pontoons keep the floating suction as close to the surface as practical at all times. Swivel joint An external floating indicator verifies that the floating suction is operating properly, and it also provides a rough / estimate of existing product level within the tank. Double Bottom With few exceptions, whenever we remove a tank for inspection, repair or for any other reason, where the interior of the tank is accessible we install a "double bottom." While most of the industry does not do this because of the high initial cost, and no other company has a uniform policy of upgrading their distribution tank population to double bottoms, Chevron does. We believe that it pays out both environmentally and economically in the long run. The double bottom is the best and most time -tested leak detection, leak monitoring and leak prevention technology that exists today. We have also found that it extends the life of the tank bottom because corrosion is reduced. Chevron has found the life cycle costs for retrofitting existing tanks with double bottoms to be competitive with conventional repair methods. Tank wall Concrete leak detection grooves Coating Leak /I detection Primary barrier— sump new steel bottom — — � — — — — — Concrete barrier and spacer (*see note below) Old / Leak High density L Five barriers bottom detection polyethylene protect the barrier port (80 mil) barrier groundwater Note. While many companies use sand as a spacer for a double bottom tank, Chevron uses polypropylene reinforced concrete. Although this is more costly, the concrete creates a sidewalk -like surface upon which to construct the new bottom, providing better welding control, less leaks, and a more accurate tank bottom slope for complete water removal. Concrete is also alkaline, so it provides additional protection against underside corrosion and extends the life of a new tank bottom beyond that of a sand spacer. Tank shell Sealed bulkheads prevent liquid from moving around the Shoe annular pontoon sections— seal this ensures floatation even if any compartment is leaking or flooded Floating suction ensures the cleanest and brightest stock is always delivered to customer New Tank Construction Our new tank construction uses four barriers of protection, and provides the same purpose as retrofitting an existing bottom. Tank wall Four barriers protect the groundwater Internal Concrete tank leak coating detection grooves Concrete slab High density% polyethylene Sand layer barrier Concrete ringwall foundation