Is it secondary containment or primary (i.e. is it a tank or something?)? Here are a few thoughts:
Are you in a hurry to fix this? If not, it might be worth setting up a few crack gauges and waiting a while to see if this problem is stable or if stuff is getting worse or changing. This might not be necessary if the cause is obvious. A crack from construction issues, shrinkage or a reasonably stabilized settlement can be repaired with most things, but thermal movement, active settlement, or structural cracks might need consideration for movement. If you have cracks at your containment area corners because the walls are long and there's thermal forces pulling at a badly detailed joint, you're just going to have it open back up again six months after you fix it with a resin, but you might be able to fix it by sawcutting and using a flexible joint filler of some sort. You should have a good theory about the cause of cracks before you try to fix them. You aren't necessarily going to be right, but you should be comfortable justifying an opinion to people.
If you don't know where it's leaking you should probably figure that out. Are you sure there's leaks? Is it cracks? Maybe it's bad construction joints or the construction isn't what you think it is. Can you fill it up for a few days to pressure test it and see what's happening
If it's secondary containment, it might not be all that urgent if they're small cracks and it's a slow seepage problem where the far side of the wall just gets a bit wet or drips Owners should fix these things, but if it's not going to cause hazard to life or environment in case of a failure of the primary containment, the way you would approach the problem and communicate it to the client is different. The difference between "Oh my god you don't have secondary containment" and "You should probably implement an operational maintenance program." It also depends on what the material being contained is.
Is it a large scale problem? If they're non-structural cracks, is it going to be easier to just spray apply a liner on the inside or place a poly liner of some sort? It might be, if the problem is everywhere. Crack repair is fiddly.
I have also had pretty good experiences with Sika in this area. They can only help you solve the question you pose to them, though, so you need to know the problem you're trying to solve.