Groundwater from the Fukushima No. 1 nuclear power plant will be released into the Pacific Ocean starting next week, the plant’s operator, Tokyo Electric Power Co. (TEPCO) has announced.

The discharge is planned to prevent the water from being further contaminated by radioactivity from the nuclear reactors damaged or destroyed by the March 2011 earthquake and tsunami.

TEPCO spokesperson Mayumi Yoshida told Bloomberg on May 16 that the initial discharge of 560 metric tonnes will happen after results of radioactivity tests are shared with local fishermen and government officials.

More than 1,000 storage tanks have been constructed at the site to hold radioactive water since the 2011 disaster, and almost a half-million tonnes of the contaminated fluid were being held there as of April 22.

Abouit 400 tonnes of water per day seeps into building basements and pits on the site. The new bypass will divert about 100 tonnes of that per day before it gets too contaminated by mixing with already radioactive water.

Local fishermen represented by the Fukushima Prefectural Federation of Fisheries Co-operative Associations agreed in April to try the diversion, subject to third-party independent verification of radioactivity tests.

In addition to tests by TEPCO, according to the Japan Times on May 15, the Japan Chemical Analysis Center and the Japan Atomic Energy Agency conducted tests.

TEPCO said strontium-90 was undetectable and cesium-137 and -134 were below safety thresholds. Asahi Shimbun reported on May 15 that tritium levels in the water tested at between 220 and 240 becquerels per litre (the safety standard is set at 1,500 becquerels).

A pump mishap announced by TEPCO on April 14 dumped 200 tonnes of contaminated water into building basements at the site. That water, used to cool reactors and containing tens of millions of becquerels per litre of cesium, was in no danger of leaking out from the buildings, according to TEPCO.

That accident occurred after a series of leaks and mishaps since August of 2013, including one that saw 300 tonnes of highly contaminated water breach a storage tank’s barrier and disappear into the ground.

Just days before that August incident, TEPCO admitted that 300 tonnes of extremely contaminated groundwater was leaking into the Pacific Ocean every day and might have been happening at that rate since March 2011.