Around 500,000 cubic meters of soil contaminated with the deadly chemical dioxin at the airport in Dong Nai Province, an hour’s drive from downtown Ho Chi Minh City, will be processed with expert assistance.

A 2016 U.S.-Vietnam joint environmental assessment found the volume of dioxin contamination at Bien Hoa, a former U.S. airbase, makes it the largest hot spot in Vietnam.

The objective is to first eliminate the risk of further dioxin migration off base, working with Dong Nai authorities to clean such areas, then treat and contain contaminated soil, the U.S. Consulate General in HCMC confirmed in a statement.

The U.S. government has committed $300 million to restoring the airbase and surrounding areas, which will take 10 years to complete and is divided into two phases. The project is expected to cleanse 150,000 cubic meters of soil by 2025 during its first phase.

The initiative kicked off several months after nine U.S. senators touched down at the military airport to officially launch the cleanup.

Senator Patrick Leahy said the Bien Hoa cleanup project follows the successful collaboration between USAID and Vietnam’s defense ministry to tackle contamination at Da Nang Airport, removed from the official list of dioxin contaminated spots in Vietnam in 2017.

Bien Hoa, now serving only military training purposes, was the largest U.S. military base in Vietnam during the war and at one time, was judged the busiest airport in the world.

Officials from Office 33, the national agency tasked with handling the consequences of toxic chemicals used by the U.S. during the Vietnam War, said at a meeting in 2012 that some spots at the airport showed the highest levels of dioxin contamination in the world, at 1.18 million parts per trillion (ppt). Dioxin concentration at the air base ranges from 1,000ppt upwards, with 100ppt considered high.

Vietnam still has 28 dioxin hotspots, including airports formerly used by the U.S. military during the Vietnam War.

The government hopes to complete the task of decontaminating the country’s soil by 2030.

Between 1961 and 1971, the U.S. army sprayed some 80 million liters of Agent Orange over 78,000 square kilometers (30,000 square miles) of southern Vietnam.

Dioxin, a highly toxic chemical contained in the defoliant, stays in the soil and at the bottom of lakes and rivers for generations. It can enter the food chain through meat, fish and other animals, and has been found at alarmingly high levels in human breast milk.

Between 2.1 to 4.8 million Vietnamese were directly exposed to Agent Orange and other chemicals before the war ended in April 1975. These chemicals have been linked to cancers, birth defects and other chronic diseases.