2-4-5T and a bunch of other nasties (Dioxins). That's bad industrial waste, not radioactive but still, you really don't want it near your village or water supply.
Those vats were stored there at the end of the Vietnam war and conveniently forgotten (by Philips Duphar). It was only about 10,000 barrels of junk, a very small fraction of your initial 32x32x32 meter cube, less than 10%.
It took decades to clean it all up, and some parts of it will never be cleaned up because we can't dig deep enough. Because in the meantime the Dioxin had made it into the groundwater plume, the damage of which will not be known for another couple of decades.
If that had been radioactive waste they wouldn't have been able to do much about it for another couple of hundred years.
I don't follow your push to minimize this problem, it is a huge issue and just thinking of a 'a single city made of high-level radio active waste' makes my skin crawl. Such a place should not exist, and the Philips-Duphar story should give you at least one datapoint on why burying stuff and letting future generations deal with it so we can have our perks today is not - in my opinion - a viable strategy.
Energy is a great thing but we are not lacking for energy at all, it's raining energy continuously, we are awash in it. But just like with a rain of soup, if you bring a fork you're not going to do much.