State regulators are requiring the U.S. Department of Energy to increase monitoring of waste at the Nevada National Security Site and establish new preventative protocols to address violations after the agency shipped unapproved low-level radioactive waste to the site for years.

The monitoring and new policies were detailed in a settlement agreement released on Thursday by the Nevada Division of Environmental Protection. The settlement, signed last month, comes after the Energy Department, over many years, shipped more than 30 packages of unapproved low-level radioactive waste from a facility in Oak Ridge, Tennessee to the Nevada security site.

In announcing the settlement Thursday, the state agency said that the unapproved waste is being safely stored at the site and does not pose a risk to public health or employees at the security site. The state said the waste will remain at the site. 

The settlement agreement includes a lengthy list of requirements that the Energy Department must follow, including a procedure to prevent unapproved waste shipments from reaching the site, additional groundwater monitoring protocols and a modified waste management permit. 

The Nevada National Security Site, once a facility for above-ground nuclear testing that led to significant pollution, sits in Nye County. Today the federal government uses it to maintain the nuclear stockpile, dispose of waste, train first responders and for high-hazard experiments.

The shipments, which occurred from 2013 to 2018, came to light in July 2019 after Gov. Steve Sisolak released a letter seeking more information about the waste shipments from then-Energy Secretary Rick Perry. Sens. Catherine Cortez Masto and Jacky Rosen also signed the letter.

“Although [the Department of Energy’s] unapproved waste disposal was an unfortunate misstep, we are thankful that this experience has helped lead the way to significant improvements that will further protect public health and the natural environment for generations to come,” Greg Lovato, who leads the Nevada Division of Environmental Protection, said in a statement.

After conducting an investigation, state environmental regulators found that the shipments of low-level radioactive waste failed to comply with the waste permit rules for the site and issued a violation to the federal agency. According to a press release, state officials then entered into a 10-month mediation with the Energy Department, a process that resulted in the settlement.

In a statement, a spokesperson for the Energy Department called the settlement "a mutually beneficial resolution."

"The final agreement builds upon the Department’s continued commitment to enhancing the rigor of its waste management activities for the protection of the DOE workforce, the public, and the environment," the statement said.

The low-level radioactive waste shipments are separate from the Energy Department’s secret transfer of weapons-grade plutonium to the Nevada security site. That material, still at the site, is set to be removed by 2026 as part of a deal that was negotiated by Cortez Masto.

Update: This story was updated on July 8, 2021 at 1:42 p.m. to include a statement from the Department of Energy.