Five months ago Tepco admitted strontium-90 levels in Fukushima Daiichi’s groundwater were much higher than what had been revealed publicly.
Reuters, Feb. 12, 2014: [Tepco] still lacks basic understanding of measuring and handling radiation, Nuclear Regulation Authority (NRA) Chairman Shunichi Tanaka said […] groundwater drawn from a monitoring well [No. 1-2] last July contained a record 5 million becquerels per litre of dangerous radioactive strontium-90 – more than five times the total beta radiation reading of 900,000 becquerels per litre recorded in the well, which is around 25 metres from the ocean. Tepco said there was a calibration mistake with one machine measuring strontium levels of well water at the plant, and it had also found an error with devices that decipher all-beta radiation. […] A Tepco spokesman said the utility will re-check all-beta radiation readings of groundwater in light of the record strontium levels.
After nearly half a year, Tepco has finished re-checking the all-beta radiation readings — and it appears the results are only being published in Japanese — Detailed analysis of Fukushima port, discharge canal, seawall — Corrected Version, RELEASED June 20, 2014 (English translation here):
Note the strontium-90 concentration in the July 5 sample is 74% of the total amount of beta radiation. Based on this ratio (25 : 34), the post-filtration strontium-90 concentration for the July 9 sample would be nearly 30,000,000 Bq/liter.