Tepco says the groundwater being dumped into the sea flowed from nearby hills and met radiation safety levels.
The controversial move followed an agreement with local fishermen.
The so-called Bypass System aims to prevent groundwater seeping into the basement of the stricken plant, and becoming contaminated.
Presenter: Sen Lam
Speakers: Ken Buesseler, senior scientist at the Woods Hole Oceanographic Institution, Massachusetts, United States
BUESSELER: The Pacific Ocean's already been impacted by contaminated groundwaters and so I would need to see what is in that groundwater, what are their levels. They're really talking about diverting groundwater from areas that are not contaminated, so they don't collect as much water in those buildings. And so, theoretically that makes some sense. But until we see numbers it's hard really to evaluate what the levels of radioactivity are, not the volume, but how much and which isotopes are going in the ocean.
LAM: And as I understand it the groundwater flows from nearby hills. Those hills would not have been contaminated by the Fukushima disaster, would they?
BUESSELER: Correct, so you'd want to know hydrologically, where they're drawing the water from, is it truly upstream from all the multiple sources of contamination on site?
And then, when they re-release it, if you divert that water flow, what does that do to the stability of the site itself, the soils or things happening such as saltwater intrusion. Would you get a flow back of the ocean water, now that you're not letting all of the fresh water out? Those are pretty key questions to know before you can say whether it's a good idea or not.
LAM: TEPCO of course says there were stringent radiation checks before the groundwater was released. How accurate are these checks?
BUESSELER: Well, people have lost confidence in TEPCO whether they're accurate or not. And so I think that's going to be one problem with the public acceptance of this, without some sort of independent review and analysis, the public maybe sceptical of what they're hearing from TEPCO at this point.
LAM: So you think it would be helpful if the data were independently verified?
BUESSELER: Most definitely. I think they really have a challenge rebuilding the public trust in general, whether it's this particular operation, schemes like the ice dam we've heard about, the purification. There're over one-thousand tanks on site, several of which have leaked already, and what are they going to do with that water, that's going to take rebuilding the confidence of the public to say that when it is released they've actually brought it to safer levels and that that's acceptable.
LAM: And we've also had reports of a treatment plant breaking down. How much does this further compound the problem and the challenges faced by TEPCO?
BUESSELER: They've got an enormous challenge in getting online something they can process hundreds of tonnes per day of this radioactive water to remove isotopes like Strontium-90, that's called the ALPS system. And they've taken over what's close to three years, but they've been working on that for a couple of years and not brought that to the point where it's functional.
So every day if you think about it, there have been, every two days, put up a new tank and store water in there until they can actually clean it up. One of their first priorities has to be clean-up of what they've already collected, but they've been unsuccessful so far at doing that.
LAM: And three years after the Fukushima disaster, might the radiation levels have diminished somewhat?
BUESSELER: Well certainly in the ocean, they were say for one of the more abundant isotopes, caesium 137 and 134, much, much higher than three years ago right after the accident.
On the other hand, there's still leaking, they're still at levels that are causing concern in terms of things like fisheries they're still closed in that local area, and that is largely due, most likely to continued leaks from the site.
So we have a situation that I say it's hardly under control, when they can't control the groundwater and they can't clean up the radioative waters they've already collected.
LAM: The Pacific Ocean is a vast area - Would it be big enough to absorb some of that radiation and contaminated water, if indeed any's been released there?
BUESSELER: Yes certainly the concentrations decrease hundreds of thousands of times even short distances offshore.
Now we're trying to detect the arrival of some of the radio-nuclearites from three years ago on the west coast of North America and don't see yet that radioactivity.
But it will be many, many times smaller, thousands or a hundred thousand times smaller than there in Japan.
So that is a positive but there's also concern locally in Japan about things like fisheries and longer term accumulation on the sea floor, where it wouldn't be moving away from Japan at that point, it would be staying near the coastline.