https://en.wikipedia.org/wiki/Burn_pit
A burn pit is an area of a United States military base in which waste is disposed of by burning.
According to the United States Army field manual, there are four other ways outside of burn pits to dispose of solid waste: incinerators, burial, landfills, and tactical burial.
The waste burned using burn pits included chemicals, paints, medical waste, human waste, metal and aluminum products, electronic waste, munitions (including unexploded ordnance), petroleum products, lubricants, plastics, rubber, wood, and food waste. A typical burn pit uses jet fuel (usually JP-8) as the accelerant.
https://grist.org/health/military-burn-pit-health-effects-veterans-overseas-domestic/
How the U.S. military’s toxic burn pits are poisoning Americans — overseas and at home
The burn pit sprawled across nearly 10 acres of Joint Base Balad, a U.S. air base 50 miles north of Baghdad. Plumes of noxious black smoke rose from the pile, which contained a long list of detritus from the base’s daily operations: Styrofoam containers from the dining hall, batteries, metals, plastics, paints, petroleum products, medical waste, amputated limbs, sewage, discarded food, ammunition, and more — all of it doused in jet fuel and kept smoldering 24 hours a day, seven days a week.
The Department of Defense currently operates 38 toxic burn sites in the U.S., mostly in low-income, rural communities. At these sites, the military collects excess, obsolete, or unserviceable munitions, including bullets, missiles, mines, and the bulk explosive and flammable materials used to manufacture them, and destroys them by adding diesel and lighting them on fire, or by blowing them up. Last fiscal year, the Department of Defense destroyed 32.7 million pounds of explosive hazardous waste on U.S. soil using these methods, known as open burning and open detonation.