RENO, Nevada (AP) -- Fifteen years after U.S. regulators started assessing damage and health risks at an abandoned Nevada copper mine, the Environmental Protection Agency is moving to add the contaminated site to its Superfund National Priority List, according to documents obtained by The Associated Press.
Rural neighbors of the World War II-era mine that has leaked toxic chemicals for decades won a $19.5 million settlement in 2013 from companies they accused of covering up the contamination -- some of it radioactive -- near Yerington, 65 miles (105 kilometers) southeast of Reno.
The EPA sent a letter to Gov. Brian Sandoval this week announcing the agency's intention to place the mine on the list of the nation's most polluted sites to "mitigate exposures that are a substantial threat to the public health or welfare or the environment."
Nevada has opposed past EPA proposals to list the site, based on fears about the impact on property values, as well as any precedent of federal intervention in the mining-friendly state that is the world's sixth-biggest producer of gold.
But earlier this year, the Nevada Division of Environmental Protection estimated it would cost $30.4 million to address only what EPA considers the most immediate health and safety concerns, and the state has been unsuccessful in obtaining financial assistance from those responsible for the damage.
Under the Superfund listing scenario, the EPA would cover 90 percent of the costs.
"Without an identifiable private source of funding, the only mechanism to make federal funding available is to add the site," to the Superfund list, said Jared Blumenfeld, the EPA's regional administrator in San Francisco.
Aides to Sandoval had no immediate comment.
The class-action lawsuit filed in 2011 accused Atlantic Richfield Co. and its parent company, BP America Inc., of "intentionally and negligently" concealing the extent of uranium, arsenic and other pollutants leaking into their drinking water wells from the mine on land owned partly by the U.S. Bureau of Land Management.
Previous owners left behind 90 million gallons of acidic solution that continues to threaten the groundwater, Blumenfeld said.
Peggy Pauly, a Yerington minister's wife, helped organize efforts to demand additional cleanup and filed the lawsuit joined by about 700 neighbors.
"She's the real hero in all of this," said Steven German, a New York-based attorney who represented the residents.
Anaconda produced 1.7 billion pounds of copper from 1952 to 1978 at the mine in the Mason Valley, an irrigated agricultural oasis in the largely barren high desert. The EPA determined the uranium was a byproduct of the copper and that the radioactive waste was initially dumped into dirt-bottomed ponds that -- unlike modern lined ponds -- leaked into the groundwater.
EPA studies showed 79 percent of the wells tested north of mine had dangerous levels of uranium or arsenic or both. At the mine itself, wells tested as high as 100 times the standard.
The EPA says long-term exposure to high levels of uranium in drinking water may cause cancer and damage kidneys.