No one knows from where, or how, but ever since the higher levels of radioactive cesium started to get detected from the groundwater samples in the observation holes along the seawall at the plant 3 days ago (July 8), particularly in the hole No.1-2, TEPCO's explanation up to that point became, obviously, invalid.
TEPCO had said that the high levels of tritium and all-beta in the groundwater samples were from the extremely highly contaminated water that leaked from a crack near the Reactor 2 water intake in early April of 2011, and that the soil had absorbed radioactive cesium and that was why the water samples were showing very low levels of radioactive cesium.
That explanation went out the door when 9,000 Bq/liter of cesium-134 and 18,000 Bq/liter of cesium-137 were detected from the hole No.1-2.
The Nuclear Regulatory Authority finally ran out of patience, and took up the subject in their regular press conference on July 10. Chairman Tanaka said it was now possible that the plant had been leaking contaminated water into the ocean for the past two years and 4 months. The same day, TEPCO's PR tried its best not to commit to anything by avoiding explanation. (Here's an article by NY Times' Hiroko Tabuchi, an admirable effort to make sense of extremely confusing press conferences by both NRA and TEPCO.)
But now, TEPCO has come up with the new explanation: It is the dirt particles in the water that are highly radioactive with cesium, not the water itself.
To prove it, TEPCO filtered the water using 0.45μm filter, and measured the radioactivity. Lo and behold! The numbers for cesium went down, to 1/100 of the numbers before filtration! Sigh of relief at TEPCO, no doubt.
That still doesn't explain the high levels of tritium and all-beta.
TEPCO's handout for the press (English) (7/10/2013):
(Click to enlarge)
The plan is still on, by the way, to release groundwater that is being pumped into tanks upstream to the ocean. TEPCO/government is still trying to obtain consent from the fishery association of Fukushima Prefecture. Some of local fishermen are saying, according to Tokyo Shinbun, that it doesn't matter anyway, as no one will buy fish caught off the coast of Fukushima anyway.
Once Abe and his minister in charge of countering baseless rumors (aka radioactive materials) have their way after the Upper House election, the fishermen will get to sell their catch, I'm sure.