The river, Aburasawa River, flows into Kitakami River, the largest river in Tohoku and used for water supply.
From RSOE EDIS Event Report (2/27/2013):
The equivalent of 125,000 lethal doses of cyanide leaked from a factory in Japan after a snowplough accident, a plant operator said Wednesday. At least five tonnes of liquid waste containing sodium cyanide spewed out of a tank after it was hit by a snowplough at a plating factory run by Kurosaka Plating Co. in Hanamaki, northern Japan, on Tuesday, a company official said. One litre of the toxic liquid waste, used to remove nickel plating from surfaces, is enough to kill 25 people, the official said. The leak occurred when workers were trying to remove piles of snow from the site, which has seen severe winter weather over the last week, and damaged a valve on the tank in which the chemical was stored.
"Fortunately, snow absorbed most of the liquid and we have been able to collect the contaminated snow," the official said. "The leak has not reached a nearby river and we have not received any reports of impact on people."
As Iwate Nippo reports it (2/27/2013), the company who operates this factory and the Iwate prefectural government sat on the accident for more than one day before they admitted to the incident. To summarize Iwate Nippo's article,
The accident happened at 7AM on February 25 when a snow plowing machine slammed into the valve of the storage tank.
The company, Kurosaka Plating Co. headquartered in Tokyo, did alert the city of Hanamaki where the factory is located.
The city conducted the water sampling tests of the reservoir in the industrial park where the factory is located, and the nearby Aburasawa River.
The city finally decided to say something about the accident on February 26.
No leak into Aburasawa River.
However, later Yomiuri Shinbun article (2/27/2013) says there was a leak into the river:
5.9 milligrams per liter of sodium cyanide was detected in the reservoir of the industrial park [in the February 27 testing], 1.4 milligram/liter where the reservoir drains to Aburasawa River where on February 26 evening 0.7 milligram/liter had been detected. At two locations downstream on Aburasawa River, 0.1 milligram/liter was detected. It was ND at other locations. The city has piled up sandbags to prevent the leak from the reservoir into the river, and has stopped the water intake at Kitakami River into which Aburasawa River flows.
The maximum amount of cyanide allowed in waste water is 0.1 milligram per liter.
Whether it is a nuclear accident or a chemical accident, Japan seems to respond the same anyway - not telling anyone anytime soon so as not to cause panic among the general public, when in fact it is the government officials and the companies involved who panic.
(And their favorite tools are sandbags and duct tapes. Well, they work.)
So, while the city disclosed the leak at the factory one day late on February 26 the leak continued into Aburasawa River then into Kitakami River for another day.
(H/T reader Helios)