Tokyo Electric Power Co. began dumping groundwater from the Fukushima No. 1 nuclear plant into the Pacific on Wednesday, in a bid to manage the huge amounts of radioactive water that have built up at the complex.

The utility, which says the water discharged is within legal radiation safety limits, has been fighting a daily battle against contaminated water since Fukushima No. 1 was decimated by the earthquake and tsunami of March 2011.

Tepco said 560 tons of groundwater captured and stored before it entered reactor building basements was to be released Wednesday, using a bypass system that funnels it toward the ocean after checking for radiation levels.

Using the bypass, Tepco hopes to divert an average of 100 tons of untainted groundwater a day into the ocean.

The controversial release, which was agreed to by local fishermen after extended talks, came after the latest breakdown earlier in the week of a water treatment system for the highly contaminated water held in makeshift tanks. It also came amid revelations this week in the Asahi Shimbun that the majority of workers at the plant fled during the height of the meltdowns after the quake and tsunami knocked out cooling and backup power.

The next discharge into the Pacific is expected to involve about 790 tons of groundwater stored since last year, although a Tepco official stopped short Tuesday of saying when that may take place.

Tepco plans to step up the rate at which it pumps groundwater from the wells and feeds into tanks. If Wednesday’s procedure becomes a routine cycle, the official said there could be a discharge of waterroughly every week.

The safety limits for the water released, which Tepco says are tighter than World Health Organization guidelines for drinking water, state that released groundwater should contain less than 1 becquerel per liter of cesium-134 and cesium-137, 5 becquerels of beta ray-emitting radioactive material such as strontium-90, and 1,500 becquerels of tritium.

The water discharged on Wednesday was pumped last month from wells uphill of the reactors and stored in tanks, in a cycle that aims to reduce the amount seeping into heavily contaminated ground and into the building basements. Tepco pumped a total of 560 tons of groundwater from wells above the plant between April 9 and 14 and tested it ahead of the release.

At the Fukushima No. 1 complex, groundwater flows down from nearby hills and 400 tons enters the basements of the wrecked reactor buildings on a daily basis, according to Tepco’s estimates, mixing with highly radioactive water used to cool reactors.

Workers then pump out the contaminated water, treat it and store it in more than 1,000 makeshift tanks that cover the facility grounds. The tanks that hold the most contaminated liquids are nearly full and workers are rushing to build more capacity.

But Tepco also wants to prevent a major increase in the total amount of water it needs to store. A Tepco official said if the so-called groundwater bypass is found to work, it is projected to reduce the water reaching the reactor buildings by up to 80 tons per day.

Meanwhile, the facility being used to treat the water, the Advanced Liquid Processing System (ALPS), which is designed to remove the most dangerous nuclides, was completely shut down again this week. The system has not been fully operational since it was installed nearly two years ago.

The manager of the plant has admitted the repeated leaks and equipment malfunctions are “embarrassing.”

According to the Asahi Shimbun report Tuesday, which cited unreleased transcripts of interviews with the crippled plant’s manager at the time, Masao Yoshida, about 90 percent of Tepco workers defied orders and left the Fukushima No. 1 plant on March 15, 2011, after an explosion rocked the site. Yoshida, widely viewed as a national hero for taking decisive action in the critical days and weeks of the disaster that prevented a more serious crisis, died of cancer last year.

Fukushima fishermen had opposed plans to release groundwater for more than two years, fearing it would cause even more damage to the reputation of produce from the region.

In March, local fisheries unions approved the plan, calling it a “painful decision,” but necessary to stem the tide of radioactive water piling up at Fukushima. Many of them have been out of work after a voluntary ban on fishing in the area.