On 2/22/2015, Tepco announced the radiation level suddenly jumped up in the plant area drain to let it flow to the sea.
According to Tepco, 2 radiation monitors detected the rapid increase of all β nuclide density (to include Strontium-90) around 10:00AM.
The indicated radiation level was 5,050,000 〜 5,630,000 Bq/m3.
It made Tepco check the potential leakage of the contaminated water tanks upstream and contaminated water transferring system, but they did not shut down the drain outlet for nearly 3 hours for some reason.
Extremely high level of all β nuclide was detected from seawater near the outlet, which was 3,000,000 Bq/m3. The contaminated water flowed to the sea.
The highest density detected by the monitor was 7,230,000 Bq/m3, which was 10 〜 100 times much as usual.
After all, Tepco found no leakage from contaminated water related facility upstream. There is a possibility that highly contaminated groundwater moved and flowed to the drain.
Currently they are collecting the water from drain by vacuum truck.
Source: Fukushima Diary