So it might take years for the treated water to reach South Korea, but in water samples taken in the vicinity of the East coast of Japan a higher than expected dose of radiation would show up almost immediately after release. And of course the concentration will always be strongest off the coast of Fukushima, so if concentrations are higher than expected off the coast of Japan, they could immediately stop releasing the treated water, and the concentration by the time it reached Korean waters would be orders of magnitude lower (note the colors on the dispersion graphs represent exponential changes in concentration) than what was detected near Fukushima.

That’s what I mean when I say anyone who really wants to can conduct their own tests and sound the alarm. Hell, if the Chinese government wants to pay me I’ll go take a boat off the coast of Fukushima and collect some water samples for them myself.