Due to poorly educated workers at my nuclear power plant, I was told that a meltdown was imminent at my power plant. Considering how densely packed my city is, I didn't fancy having a meltdown and removed the nuclear power plant in favour of an oil power plant.

However, it seems that some contamination of the area has still occurred. Sims living and working nearby are now getting sick from the contamination. How long does it take for the radiation contamination to completely dissipate?

Here's a screenshot showing the contamination:
![enter image description here](https://i.stack.imgur.com/6sGh1.jpg)