(Corrects date of New Mexico emergency declaration to Monday from Tuesday, paragraphs 1, 15, fixes spelling of Sinjin Eberle's first name, paragraph 7)
By Steve Gorman
Aug 11 (Reuters) - New Mexico officials have joined Colorado in declaring an emergency due to toxic wastewater spewing from an abandoned gold mine, a spill that prompted authorities to close two rivers to drinking water and irrigation intakes for at least another week.
The San Juan River and its northern tributary, the Animas River, have been fouled by the release of more than 3 million gallons (11.3 million liters) of acid mine drainage inadvertently triggered by a team of Environmental Protection Agency workers last Wednesday.
The discharge has continued to flow at the rate of about 500 gallons (1,900 liters) a minute from the site of the century-old Gold King Mine, near the town of Silverton in southwestern Colorado, into a stream below called Cement Creek.
From there, the wastewater has washed into the Animas River and into the San Juan River in northwestern New Mexico.
The bright orange contamination plume, containing heavy metals such as arsenic, mercury and lead, has dissipated through dilution as it spreads downstream, with its leading edge no longer visible from aerial surveys, the EPA said
"From initial sampling, as the plume has advanced, we are seeing elevated levels (of contaminants), but as it moves on we are seeing a downward trajectory toward pre-event conditions," EPA chief Gina McCarthy said at a clean-energy event in Washington.
The Animas River in Durango, Colorado, about 50 miles (80 km) south of the spill, had turned bright, lime green by Sunday, and was a darker shade of blue-green by Tuesday, a sign that pollutants were gradually clearing, at least near the surface, said Sinjin Eberle, a spokesman for the conservation group American Rivers.
But experts said a long-term concern was the deposit of heavy metals from the spill that had settled into river sediments, where they can be churned up and unleash a new wave of pollution when storms hit or rivers run at flood stage.
An unspecified number of residents who live downstream from the mine and draw their drinking supplies from private wells have reported water discoloration, but there has been no immediate evidence of harm to humans, livestock or wildlife, according to EPA officials.
Still, residents have been advised to avoid drinking or bathing in water drawn from wells in the vicinity, and the government is working to supply water as needed to homes, ranches and farms.
Two Colorado municipalities, including the city of Durango, and the New Mexico towns of Aztec and Farmington have shut off their river intakes, the EPA said.
EPA officials said the Animas and San Juan rivers would remain closed until at least next Monday to such uses as the supply of drinking and irrigation water, and fishing and recreation as experts try to gauge safety risks posed by the spill.
Wastewater still escaping from the mine site was being diverted into hastily built settling ponds where the effluent is treated before it empties into Cement Creek, sharply reducing its acidity and metal levels, the EPA said.
New Mexico Governor Susana Martinez declared a state of emergency on Monday, freeing up an additional $750,000 for disaster response, and said she was directing her administration to "be prepared to take legal action against the EPA."
Colorado Governor John Hickenlooper declared his own "state of disaster" emergency on Monday, and vowed to take actions to "make sure this doesn't happen again."
Colorado has more than 4,000 abandoned mines, about 1,100 of them around Silverton, according to American Rivers, which calls those sites "ticking time bombs."
The Navajo Nation has also been affected. Its sprawling reservation is traversed by the San Juan River, which flows through southeastern Utah into Lake Powell.
It was uncertain how far significant contamination from the spill would travel, but EPA officials said on Tuesday the leading edge of the original burst of contamination had moved well beyond Farmington. (Reporting by Steve Gorman in Los Angeles; Editing by Peter Cooney)