Editor’s note: This story has been updated to include comment from the Department of Energy.

Unapproved low-level radioactive waste was shipped to Nevada over the past six years, according to a letter Gov. Steve Sisolak sent last week to U.S. Energy Secretary Rick Perry.

From 2013 to 2018, the Department of Energy (DOE) made several shipments of low-level radioactive waste from DOE’s Y-12 facility in Oak Ridge, Tenn., to the Nevada National Security Site (NNSS), according to the governor’s office. The last shipment arrived at NNSS in December 2018.

The shipments violated the Security Site’s Waste Acceptance Criteria that determine the kinds of low-level waste suitable for the site.

“These egregious acts — whether acts of negligence or indicative of something else — are unconscionable and have potentially put the health and safety of Nevadans and our environment at unacceptable risk,” reads the letter sent July 5 to Perry. It was signed by the governor as well as U.S. Sens. Catherine Cortez Masto and Jacky Rosen, both Democrats.

There is a disagreement in the total number of shipments made. In a statement, the governor’s office said they were told there were a total of 32 shipments made but the DOE disputes that number saying there were only 9.9 shipments with a total of 32 containers delivered.

While the DOE confirmed that the shipments were not in compliance with its waste acceptance criteria they said the shipments posed no risk to health and safety.

“The components that were shipped pose no risk to the safety and health of the general public or workers at the facility at NNSS. The Department’s National Nuclear Security Administration has launched an internal investigation to determine how this went undetected for a six-year period,” the department said in a statement.

Sisolak learned about the shipment from the DOE on July 3, and was informed that they may have included “mixed-low level radioactive waste,” which has never been approved for disposal at the NNSS. The DOE later said it has not yet determined whether the shipments included Mixed Low-Level Waste, which is regulated more stringently, as opposed to Low-Level Waste.

After a briefing on July 9, Sisolak said he “was beyond disappointed to learn of problems related to shipments of low-level radioactive waste from the DOE’s Y-12 facility to Nevada.”

“While we appreciate the courtesy of the in-person briefing, we will continue to do everything in the state’s power to hold them accountable, ensure there is a plan to fix this problem and prevent it from occurring again, and above all else, protect the health and safety of Nevadans,” Sisolak said in a statement.

The letter concluded with a request that the DOE “immediately provide all information currently known or discerned regarding the mischaracterized and illegal shipments and disposal of material from the Y-12 facility” including a timeline of when the DOE became aware of the issue.

The letter pointed out the revelation is “not anomalous” noting that the DOE disclosed earlier this year that it shipped a large amount of weapons-grade plutonium to Nevada without the state’s knowledge and called it “illustrative of DOE’s failure to respect Nevada’s sovereignty as an independent state and to adhere to the basic precepts of honesty and forthrightness, which form the basis of any relationship of trust.”

“Nevada’s trust and confidence in the Department has already been diminished by recent past events. Now, any remaining trust and confidence is at best tenuous because of the Department’s newly disclosed actions,” reads the letter.

A call for Perry’s resignation

Nevada’s congressional delegation responded swiftly and harshly upon learning of the shipments. Democratic Rep. Dina Titus called the DOE “an untrustworthy partner,” and added, “The level of incompetence at the Department of Energy is only matched by its dishonesty.”

Cortez Masto immediately called for oversight into DOE’s misclassification of the waste shipments.

“Yet again, the DOE has violated its mission, broken Nevadans’ trust and failed to follow its own compliance procedures,” Cortez Masto and Rosen said in a joint statement. “We intend to immediately determine whether the mixed waste shipped to Nevada poses a hazard to the health and safety of Nevadans and will take every action necessary to hold the DOE accountable.”

Democratic Rep. Steven Horsford called for the immediate resignation of DOE secretary Perry.

“Secretary Perry has repeatedly disrespected the people of Nevada and eroded the public trust in his ability to abide by established rules for waste disposal,” said Horsford in a statement.

“As Representative of District 4 of Nevada, which is home to the National Nuclear Security Site, I vow to investigate the past and current conduct of the DOE and hold them accountable for their dismissal of the law and blatant disregard for the safety of Nevadans. The people of Nevada adamantly oppose the storage of nuclear waste in Nevada. It is opposed by every member of the Nevada delegation, on both sides of the aisle, and has been opposed by the last five Governors of Nevada, Democrat and Republican.”

In light of the unapproved shipments, Perry has directed the department to initiate an assessment of waste shipment policies and procedures said they would “ reinforce safety training for all DOE personnel who have a role in the Department’s mission related to waste shipment certification,” according to a statement.

“The Department is committed to working closely with Nevada State Officials in an open and transparent manner to ensure concerns are appropriately and promptly addressed,” said Shaylyn Hynes, a DOE Spokeswoman, in a statement.