Sen. Elizabeth Warren, D-Mass., and Rep. Alexandria Ocasio-Cortez, D-N.Y., are urging the U.S. Senate to include a House-approved amendment to authorize $10 million for the use of closed detonation chambers in efforts to clean up military ordnance in Vieques, a smaller island located about seven miles off the southeast coast of Puerto Rico that for over 60 years served as a bombing range and site for military-training exercises.

Vieques is the most hazardous waste site in Puerto Rico, according to the U.S. Environmental Protection Agency.

Since 2003, the U.S. Navy has been using open-air detonation chambers to try to clean up ordnance that contain toxins such as Agent Orange and mercury. The military ordnance was left behind across 9,000 acres of the property by the naval warfare service branch of the United States Armed Forces after decades of military weapons tests.

The Navy's Naval Facilities Engineering Command Atlantic, which is in charge of the Vieques Environmental Restoration program, considers open detonations to be "much safer process" for site workers because they don't have to carry unexploded ordnances to a different site. They also argue "it is the quickest and most efficient way to complete the cleanup" process.

But a report from the Congressional Research Service states that a series of “environmental concerns” exist around open-air detonation practices.

The report found that closed detonation methods such as “burn trays and blast boxes” are more effective at containing pollutants and toxic emissions during military cleanup efforts.

"Residents and activists repeatedly condemned the open-air burning and detonation, and have expressed fears about the toxicity, human health effects, and environmental impacts of these practices," lawmakers said in a letter addressed to the Chairmen and Ranking Members of the Senate and House Armed Services Committees and obtained by NBC News. "We share the concern of residents that the hazardous waste and remaining munitions pose a risk of further contamination of the island and continues to threaten public health."

The letter was signed by 17 lawmakers, including and presidential candidates Sens. Warren, Amy Klobuchar, D-Minn., Kamala Harris, D-Calif., Cory Booker, D-N. J., Bernie Sanders, I-Vt., Kirsten Gillibrand, D-N.Y., and Rep. Tulsi Gabbard, D-Hawaii, as well as Puerto Rican members of Congress such as Reps. Ocasio-Cortez, Darren Soto, D-Fla., Nydia Velázquez, D-N.Y., and José Serrano, D-N.Y.

The remarks come as Congress gets ready to enter conference negotiations on the National Defense Authorization Act for 2020, a bill to authorize appropriations and policies for Department of Defense programs and activities.

"After decades of bombing exercises by our military resulted in severe harm to Vieques, we owe it to our fellow U.S. citizens on the island to clean up after ourselves in a safe, responsible way," the lawmakers wrote. "As you finalize the NDAA, we therefore urge you to include the House provision that provides funding for safe Vieques cleanup."

The language in the House amendment, presented by Ocasio-Cortez, encourages the U.S. government to purchase, deploy and operate closed detonation chambers to substantially reduce “the practice of open air burning and open air detonation to the lowest practicable level.”

In a letter sent in April, 42 organizations called out the U.S. Environmental Protection Agency and various members of Congress for not promoting the use of safer, less harmful decontamination methods in Vieques when less polluting alternatives exist.

“To date, the Navy reports that it has open air burned or detonated more than 100,000 high explosive UXO ordnance, including bombs, projectiles, rockets, grenades and submunitions as part of its environmental remediation program,” the letter reads. “By definition, open burning and detonation result in the uncontrolled release of toxic pollutants to the environment. These toxic emissions endanger public health.”

Myrna Pagan of Vidas Viequenses Valen, a local community group, said in a statement, "The people of Vieques have denounced for decades the toxic damage this practice has produced on our community, causing a health crisis. We have no hospital in Vieques to provide health care services to the victims. The open burnings and open detonations are an attack on our human rights to health and development,” she stated.

If the Senate approves the amendments, then the U.S. government will provide the $10 million needed to pay for alternative cleanup methods.

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