Chinese officials say the water in the northeastern city of Harbin will be turned back on Sunday, five days after it was cut off due to massive chemical contamination of the Songhua River. A government team, including "disciplinary officials," has begun an investigation into the chemical factory explosion that caused the contamination.

The residents of Harbin have endured four days without running water, after an explosion at a government-owned petrochemical plant in Jilin Province dumped 100 tons of toxic chemicals into the Songhua River. The river provides most of the drinking water for the approximately four million people in Harbin, the capital city of adjoining Heilongjiang Province.

The official Xinhua News Agency says the water will be turned back on at 11:00 p.m. Sunday.

The levels of the two major contaminants in the river, benzene and nitrobenzene, have been falling steadily since Friday. But officials say the level of nitrobenzene near Harbin is still several times the safe limit.

A team sent by China's central government is investigating the circumstances surrounding the petrochemical plant explosion, which occurred November 13. Xinhua said the presence of disciplinary officials on the team indicated that "punishment of irresponsible acts are on the way".

Vice Environmental Minister Zhang Lijun said in a nationally televised press conference Thursday that officials at the plant would be held responsible.

Mr. Zhang said the major organization to be held responsible would be PetroChina in Jilin province, and the chemical complex in particular.

Xinhua reports more than a thousand soldiers and workers had been working "around the clock" to install new filters at Harbin's water purifying plant, in anticipation of turning the taps back on.

Residents have been told to inspect the water for unusual colors or odors before drinking it. And there are concerns that even though the river water is declared safe, chemicals may have seeped into the riverbanks.

When the 50-mile-long spill has passed Harbin, hundreds of thousands of Chinese downstream from the city are likely to be affected. The spill is expected to reach the Russian border in about a week, and Russian officials have expressed concern for the 1.5 million people living in the Siberian city of Khabarovsk, who also rely on the Songhua for their drinking water.

On Friday, several local Chinese newspapers published unusually critical reports about the spill, arguing that local officials took too long to report the situation to those living along the river.

Harbin officials did not turn off the water until the evening of November 22, nine days after the explosion. News organizations have questioned why local residents were originally told that the water was being turned off only for "routine maintenance."