A citation for the story might be nice. But since there isn’t one, I can only talk about radioactive liquid releases in general.
Releases of radioactive liquids into the environment are generally controlled by oversight organizations. These set limits on amount and type of radioactive liquids that can be released. I say generally because I’m pretty sure China and probably N Korea do whatever the hell they want.
When a nuclear power plant releases potentially contaminated liquids into the environment, there is a huge process. Releases go on all the time from nuclear power plants. There are a number of reasons for them. But in general the process is all the same.
1) liquids that are desired to be released are first processed to help remove as much contamination as is reasonably possible (radioactive contamination).
2) The liquid is sampled and analyzed for radioactive components. Typically this involves looking for gamma, alpha and beta radiation as well as tritium. There are some methods for doing these and things like alpha, beta, and tritium may be done as a monthly composite. They can do this by showing historical evidence that if gamma activity is somewhere in the range of X, the alpha/beta/tritium are in the range of Y
3) The activity results are then processed into a formula to determine the potential impact on the environment based on the impact of dose to the public. This calculation takes into many factors such as what isotopes are present, how they may impact a person, method of impact to the person, etc. All these are assuming the worse case impact based on the isotopic mix of the sample. Example: Co-60 is considered an impact on the GI tract of an adult as the worst case whereas I-131 is considered a Thyroid impact on a child. If a sample contains both, the calculations determine impact of each isotope and then figures out which is the limiting factor based on potential damage to a human.
4) All the results are tracked for impact over time. There are limits for the release, for monthly, quarterly and annual impacts as well. All these limits are compared with the results of the proposed release being added in and if a release would end up exceeding a given limit it is not allowed to be released.
It should also be noted that not all radioactive isotopes are created the same. Some impact us more than others based on how they are absorbed into the body and what organ is being impacted the worst.
Additionally, it should always be remembered that news outlets LOVE nuclear power plants. They can write all sorts of stories that draw in readers/users. At one nuclear plant I worked at, the local paper ran an article on the front page that was entitled “ACCIDENT AT THE NUCLEAR PLANT”. The story was about a fender bender in the parking lot. And no, I’m not making that up.