A power cut at the Formosa Ha Tinh Steel plant in April led to toxic waste water flooding into the sea off the central coast, according to a government investigation seen by the Reuters news agency.
Full details of the official report, completed in July, have not been made public, fuelling allegations of a cover-up.
Thousands of local people in the worst affected provinces have defied warnings and intimidation by the authorities to demand compensation, and full government accountability, for one of the worst environmental disasters in Vietnam’s history.
Reuters reported that the investigation had uncovered fifty violations at the Taiwanese run steel mill in the run-up to the leak of contaminated water.
It said that Formosa had not kept to plans agreed in the original environmental assessments made for the project.
The report, signed off by the government and a panel of international experts, said that Formosa was using a “wet” cooling system that was more prone to toxic leaks than the more modern “dry” system.
The news agency reported that a power cut had disabled the waste processing equipment, leading to a discharge of toxic waste, including cyanide products, into the sea.
The leak led to the death of millions of fish, devastating the fishing and tourism industries in four central provinces.
Formosa has since paid $500 million in compensation, but local people supported by environmental activists, are demanding full transparency, from a government that has sought to conceal details of the leak and the clean up operation.
No government officials have been censured or subjected to any other penalties for their failure to regulate the plant effectively.
Local courts have rejected the submission of thousands of law suits by residents demanding adequate compensation for their lost livelihoods.
Formosa acknowledged that it was using the less modern cooling system, but said that it did not have to change to the safer system until 2019 under its agreement with the government, according to Reuters.
It said that it had already complied with 45 of the 53 violations identified in the official report and would finalise the other recommendations in the coming weeks.
Formosa is planning to bring the plant into full operation by next year, making it one of the region’s largest steel mills.
Campaigners say they have no confidence that all the faults have been rectified or in the government’s handling of the aftermath of the disaster. They are demanding that the plant be shut down to prevent a recurrence of the disaster.