Tokyo (CNN) -- Contaminated water was pumped Sunday from basements of two buildings at the stricken Fukushima Daiichi nuclear power plant, a Japanese official said, but authorities still don't know how to deal with liquid in one locale that had radiation levels 10,000 times above normal.
The process for removing pooled water in the turbine building of reactor No. 2, which earlier tested as having between 200 to 300 millisieverts of radiation, was to begin late Sunday morning, said Hidehiko Nishiyama, an official with Japan's nuclear and industrial safety agency. By comparison, an individual in a developed country is naturally exposed to 3 millisieverts per year, though Japan's health ministry has set a 250 millisievert per year cumulative limit before workers must leave the plant.
Two days earlier, authorities had begun the process of draining water that had collected in the No. 1 unit's turbine building -- a process that continued Sunday, according to Nishiyama.
Still there is no definitive plan on what to do with collected water in the turbine building for reactor No. 3, which had the worst radiation levels of all three sites.
"We are still in the process of studying that -- as to which way we should go (to drain the water)," said Nishiyama.
The potential for contamination from this unit, which has had a building severely damaged by a hydrogen explosion and that an official said last week might have leaked radiation from its reactor core, is of special concern because it is the only one of the facility's six reactors to use a combination of uranium and plutonium fuel, called MOX. Experts say this mix is considered more dangerous than the pure uranium fuel used in other reactors.
Morevoer, possible seepage of water-borne contamination -- potentially from the turbine buildings' basements -- gained increased urgency Saturday, when Japan's nuclear safety agency reported the amount of radioactive iodine in seawater 330 meters (361 yards) from the plant was 1,250 times above normal.
Three men laying cable in the No. 3 unit turbine building's basement have been hospitalized after stepping in water, which later tested as having radiation 10,000 times the normal level, on Thursday.
An official with Tokyo Electric Power Company, which runs the plant, apologized Saturday, saying the exposure might have been avoided with better communication.
Hideyuki Koyama, the company's associate director, said pooled water had been discovered in the basement of the No. 1 reactor six days earlier. But a sample was not taken for analysis until the 24th, after the three workers were exposed to between 173 to 181 millisieverts of radiation.
Such incidents threatened to undermine the public's trust in Tokyo Electric, Japanese Chief Cabinet Secretary Yukio Edano told reporters.
He added the Japanese government "would like to give stronger instructions" to the company that it fully disclose as much information as possible about conditions at the plant.
"Every piece of information must be provided accurately and swiftly" to Japan's nuclear and industrial safety agency, Edano said. "Without this communication, it's very difficult for the government to (establish) proper safety measures."
As important, the chief secretary said, was the need for Tokyo Electric to be upfront with the Japanese -- millions of whom get power from the company and millions more of whom have been affected by radioactive emissions stemming from the crisis.
"We need to be sure that (Tokyo Electric) isn't going to act in a way that will create distrust," Edano said.
Koyama told reporters that radiation alarms went off while the three men were working, but they continued with their mission for 40 to 50 minutes after assuming it was a false alarm.
This continued debate about the working conditions for the roughly 500 individuals -- among them utility workers, Japanese soldiers and firefighters from several cities -- comes as work continued Sunday to cool nuclear fuel at the plant and prevent the further emission of radioactive material into the air and sea.
Fresh water was being injected Sunday into the Nos. 1, 2 and 3 reactor cores, a switch from the previous policy of pumping in seawater. Those units have largely been authorities chief focus, since they were the only ones operating (and, thus, with nuclear fuel rods in the reactor cores) when the March 11 earthquake and subsequent tsunami hit.
Nishiyama said that fresh water should be injected into the No. 2 unit's spent fuel pool on Monday and No. 1 unit's spent fuel pool on Tuesday. Some nuclear fuel rods, which may have been fully or partially exposed, remain in these pools -- meaning that, if they aren't sufficiently cooled, have the potential to heat up and emit radiation into the atmosphere.
Fresh water should also be pumped, starting Monday, into the No. 4 unit's nuclear fuel pool. This suffered possible damage and has been subject to frequent external spraying of seawater, given concerns that its water levels were low and fuel rods there may be fully or partially exposed.
In addition, power and lighting were restored late Saturday afternoon to the No. 2 unit's control room, according to an online update from the nuclear safety agency. One image showed at least four individuals, wearing gear to guard against radiation exposure, working in the newly lit-up room with its banks of computers and walls of gauges and other panels.
This development is a step forward in authorities' efforts to restart a "permanent" supply of electricity to power the cooling systems, in order to control the temperatures of nuclear fuel and prevent further radioactive emissions, for that reactor and several other in the nuclear facility.
This has already occurred in the Nos. 5 and 6 units, which are considered stable has fuel rods in its spent fuel pools but not in its reactor core.
On Sunday, Nishiyama said that authorities are still deciding whether to use a temporary or "permanent" electricity supply to power the cooling systems at the Nos. 1, 2, 3 and 4 units.
CNN's Jennifer Rizzo contributed to this report