After 12 years of asking various federal agencies to clean up a federal dump they contend is leaching radioactive waste into the local aquifer, the Hopi Tribe is tired of waiting for action.

The Hopi Tribe filed a notice of intent to sue Thursday, stating that a plume containing uranium and other contaminants leaching from an open dump near Tuba City was within 2,500 feet of contaminating water supplies for two Hopi villages. The pollution left in the unlined dump — a dump created by the Bureau of Indian Affairs — is an “imminent and substantial” threat to public health and the environment, and is a result of multiple federal agencies approving Cold War-era mining and milling operations that have polluted multiple landscapes in Arizona, the tribe asserted.

The Navajo Nation has already filed a notice that they intend to sue over the same issue.

The dump was located a few miles from Rare Metals Uranium Mill, a 1950s-era uranium mill that is a federal cleanup site with documented groundwater contamination.

Federal agencies have previously responded that they thought the uranium documented in the groundwater near Tuba City was possibly naturally occurring or blown in by wind, and have requested multiple studies.

The Navajo Aquifer in the area holds water at depths of 40 feet or less in some areas, and is deeply culturally significant to the Hopi Tribe.

Some of the 1,400 residents of the villages of Upper Moenkopi and Lower Moencopi requested federal agencies conduct a full cleanup of the landfill in a September meeting at the Upper Village of Moenkopi.

“I understand that we have a shallow water plume, and then we have a deep water plume,” said Hubert L. Lewis, governor of Upper Moenkopi. “Right now the shallow water plume shows contamination of uranium almost down to one of our main roads here in the village and we’re afraid, also, that it’s going to affect one of our three main drinking wells that we utilize for domestic services.”

In response to concerns, some federal agencies offered to build a fence around the dump, saying cleanup costs for the dump ranged in the tens of millions of dollars and exceeded their budgets.

Meanwhile, village administrators working on the case say there has been a lot of foot-dragging.

“It’s been a long time for us,” said Harris Polelonema, community service administrator for Lower Moencopi. “We’ve been working on this since 1998, ’99. There has just been too many studies conducted.”

Uranium contamination in the Southwest has also been the topic of U.S. House hearings, with some members of Congress pressuring federal agencies to take action.

“I understand there was a small town in Colorado that just recently had a similar issue,” Lewis said. “And they went right in there and did the cleanup and I said to myself, ‘Just because we’re Native Americans, we’re treated as second-class people.’ And because it’s on the reservation, they seem to feel like ‘Oh, there’s no hurry.’”

Among other items, the Hopi Tribe is asserting:

— Wastes of all kinds were randomly dumped on the ground and into large trenches excavated by the BIA at the Tuba City dump.

— Commercial and medical wastes generated by various federal agencies were dumped there.

— Wastes from the nearby uranium mill were dumped there.

— Groundwater sampling shows uranium, arsenic, chromium, nitrate, selenium, and radium at the dump exceed maximum levels safe for drinking water.

— A plume containing uranium and other inorganic contaminants is flowing toward two Hopi villages.

Named in the notice of intent to sue is the Unites States, the Department of Energy, the Nuclear Regulatory Commission, the Department of Interior, the Bureau of Indian Affairs, the Department of Health and Human Services, the Indian Health Service, the Department of Defense, the Environmental Protection Agency and El Paso Natural Gas Company.

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Landfill dispute: A brief history

The Bureau of Indian Affairs opened the unlined Tuba City dump a mile east of town in the 1950s and used it for more than four decades before covering it with sand and dirt in 1997.

In addition to other trash, the dump holds uranium waste that is 10 times more concentrated than what the U.S. Environmental Protection Agency considers safe for drinking water.

The Navajo and Hopi tribes have asked various federal agencies to remove the waste for about 12 years without any success.

The radioactive waste in the dump is very similar to waste left over at a uranium mill a few miles away, according to a chemical analysis.

Other federal agencies, including the EPA, have disputed this relationship, saying the radioactive waste could have been blown in by the wind or come from other sources.

Scientists working for the tribes say the rock formations near the dump are not naturally radioactive.

From 1956 to 1966, a uranium mill a few miles from the dump processed 796,489 tons of uranium ore from the Orphan Mine at the South Rim of the Grand Canyon and from a mine near Cameron.

The Department of Energy has identified the uranium mill site as a source of radioactive pollution, and is responsible for ongoing cleanup at the mill.

But the Department of Energy has sent letters to the tribes stating that there is no proof the landfill was contaminated with radioactive waste from the uranium mill.

Neighbors living near the dump have told the Navajo Nation Environmental Protection Agency that they saw trucks from the mill dumping waste into the Tuba City dump.

The Hopi Tribe says there were no restrictions on who used the dump or on what they unloaded, and that the dump was persistently on fire.

In 2008, federal officials told residents of Upper Moenkopi that clearing out the dump would be too expensive, but that they would consider fencing it.