The Environmental Protection Agency estimates that three million gallons of mine waste had leaked into Colorado's Animas River from an accidental breach of a retaining dam last week, three times the amount disclosed earlier.
The contaminated sludge, released initially from the Gold King Mine near Silverton, Colorado, by agency workers last Wednesday and Thursday, had reached Farmington, New Mexico more than 100 miles downriver.
The agency yesterday said the discharge from the mine had not stopped. The waste, which contained arsenic, lead and mercury and other heavy metals, continued to flow at the rate of 500 gallons per minute, Reuters reported.
The report further added, that the EPA had been diverting the ongoing spill into two new settling ponds where the waste was being treated to lower its acidity before being discharged into a tributary.
While the spill was being analysed, the health risks to humans or animals remained unclear.
However, according to EPA toxicologist, Deborah McKean, due to the swift movement of the sludge after the spill, it would likely not have ''caused significant health effects'' to animals that consumed the water, the Associated Press reported.
The contaminated stretch of water is flowing down the Navajo Nation Reservation, which extends over 27,000 square miles in the Four Corners region of Colorado, New Mexico, Utah and Arizona.
Preliminary testing data the EPA released yesterday showed, arsenic levels in the Durango area of the Animas River were, at their peak, 300 times the normal level, and lead was 3,500 times the normal level.
According to officials, those levels had dropped significantly since the contaminated stretch had moved through the area.
Both metals posed a significant danger to humans at high levels of concentration.
"Yes, those numbers are high and they seem scary," said Deborah McKean, chief of the Region 8 Toxicology and Human Health and Risk Assessment. "But it's not just a matter of toxicity of the chemicals, it's a matter of exposure," Farmington Daily Times reported.
She added, those concentrations remained in one area for a short time.
Earlier yesterday the city of Durango, Colorado, and La Plata County, Colorado, declared a state of emergency. A state of emergency has been declared by The Navajo Nation Commission on Emergency Management in response to the spill.