Extremely high level of Strontium–90 was measured from groundwater of various places in Fukushima plant area, according to Tepco.
The sampling date was from this January to March. Sr-90 was measured from all of the 30 measurements.
Newer data hasn’t been published.
The most contaminated area was the seaside of Reactor 2.
The highest reading was 2,700,000,000 Bq/m3. Even the second highest reading was 1,900,000,000 Bq/m3.
Tepco doesn’t mention the most likely cause, however at least it is clear that the “large” area of Fukushima plant has Sr-90 contamination spreading.
See also.. Nuclear Expert “Fukushima plant is now like a swamp of radioactive material due to the contaminated water” [URL 2]