i-131 has a half life of about 8 days. It has been well over 10 half-lives therefore it is said to be gone by most standards. so how exactly are they worried about it now?
Because the detection of it has not ceased, doubly alarming is it coming from the childrens bodies of the surrounding communities.
The reactors fuel are in full china syndrome mode now burrowing into the groundwater level as we speak still reacting.*
Hence the reports of steam vents coming up from the ground overnight with enormously high readings like only found in Chernobyl.
*No one on the face of the planet knows for sure what the Corium is up to, (it is the most dangerous place on earth under those buildings!) but it is obvious that once it left the pressure vessel, there is only one direction the literal reacting lava (corium) will go. Down (and into the pacific and Northern Japan's water table)
3 Cores on the Floor is probably not even accurate for Fukushima anymore, all 3 corium formations only had 6 feet of concrete to go through to leave the reactor buildings foundations after exiting their drywells under the actual compromised PCV. (pressure containment vessel)
I hope that the corium did like Cherynobyl and spooged through many individual steam pipes and spread itself out into individual hot corium blobs, because it massing together in one big blob pooping out under the reactor building is not good. (keeps the reaction going/harder to cool with water from above also)
The big problem is that there are 3 reactors with individual corium blobs, any of them may have done different things. One thing is for sure, this is a all new challenge for humanity to overcome. Is it worth it?