Drums like that most likely have only low-level waste in them - stuff like contaminated tools, rags, protective clothing, sludge from the water chemistry system. There isn’t enough activity there to be of much concern outside of a few meters away.
The high-level waste would be in the spent fuel pools. This is probably the most vulnerable part of the plant, and the source of any ‘sloshed’ water. The water from the fuel pool isn’t extremely radioactive, but is is contaminated with some isotopes such as they describe, cobalt, strontium, tritium, radon - all decay daughters or induced radiation products.
why would they keep 1.2 million gallons of this sitting around in liquid form? (22k x 55gals)