Are the two pontoons which are leaking adjacent to one another? Appendix C of API 650 requires that the design of the roof be such that it can withstand a leak in any two adjacent pontoons. However, this design condition is independent of water or live load. If the pontoons are adjacent, you have a tank with no redundancy. I would investigate repair options quickly.

As for repair, API 653 requires that leaks in pontoons be repaired by rewelding of the leaking joints and/or patch plates.

The leakage could be from corrosion - how old is it? You could put plastic balls or air bags in the pontoons to take up space and keep it from getting too much worse. It should be fixed quickly though as it could be an indication that other similar failures are imminent.

The tank was constructed on 1992 but it's under scheduled refurbishment. Last one was done on 2007 and the leakage is in two adjacent potoons yes.

I think we could guess all day but until you have a chance to look at the pontoons, it will be just guessing

"You could put plastic balls or air bags in the pontoons to take up space and keep it from getting too much worse. It should be fixed quickly though as it could be an indication that other similar failures are imminent."

Twoadjacent pontoons leaking -- ya think that it may be time to do something other than "watchful waiting"? Suck out the wet compartments and airbag them ASAP. Refloating roofs is no fun. And keep a very close watch on ALL the compartments. They were made by the same company, at the same time, using the same materials. Expect similar results.