Now that it's the beginning of December, it's about the time to start worrying about ice cubes. Really big ice cubes. Like, 21,000 gallons.
I complained here and here and here about frac tanks, which we use when we need to containerize large volumes of water. That large volume of water will turn into a big problem in the winter when it starts to freeze. We do try to expedite things and button up the fieldwork for the winter, but if we're not in time to get rid of the water, it will turn into a giant ice cube and then we're stuck renting the tank until spring.
I have occasionally witnessed various attempts to un-freeze frac tanks. If you catch them before they're totally frozen (say, a couple of inches thick), you can break up the ice into giant chunks with a pickaxe or other deadly object, and toss the chunks into drums to be thawed. But once they're mostly frozen, you're looking at a huge thermal mass that you need to warm up. I have witnessed giant propane heaters aimed at the walls, elaborate warm-water recirculation plans, and other hairbrained schemes. But really, the rental fee on a frac tank for 3-4 months is not as much as it would take a crew of professionals and various bits of equipment to spend days on end trying to melt a ice cube of that size.
I will admit that I have not worked in an arctic or subarctic environment, where the threat of freezing frac tanks is present for much of the year. I assume, however, that the plan would still be the same: deal with the tanks as quickly as possible, and get them emptied and off-site before they freeze.