Window Rock, Ariz. • Officials from the Navajo Nation and the federal government are taking a closer look at more than a dozen former uranium mines on the reservation.

The tribe and the U.S. Environmental Protection Agency reached an agreement years ago to assess sites where they haven't found a mining company that would be responsible for the work. They say the work is needed before the sites can be cleaned up.

They recently named 17 sites on the reservation that will be assessed and that pose the most significant hazards. They're in the northeast corner of Arizona.

The EPA has set aside about $17 million for the assessments and a study to determine if groundwater or surface water has been affected by the mines. The work will include sampling soil and scanning for radiation on the ground surface.

Other sites that have been evaluated have had piles of uranium waste, contaminated soil and water, and physical hazards.

The work is part of a larger settlement reached between the tribe and the federal government in 2015 to assess 46 sites. The work has been broken into three parts.

The reservation covers more than 27,000 square miles in Utah, New Mexico and Arizona. About 4 million tons of uranium were extracted from the Navajo Nation between the 1940s and the 1980s. The U.S. government was the sole purchaser.

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More than 520 abandoned uranium mines dot the reservation. The last mine shut down in 1986.