The Defense Department is being asked to explain why solid waste was burned openly at an Afghanistan airbase when two fully operational incinerators were available.

A report released Tuesday by the Special Inspector General for Afghanistan Reconstruction is part of an ongoing investigation into why U.S. taxpayer-funded incinerators are going unused at many bases. It comes as the family of a 46-year-old Texas man who died earlier this month blames his death on his exposure to the toxic air emitted from burning the military bases’ waste in the open. David Thomas was a veteran of the Afghanistan and Iraq wars who died of lung cancer that spread to his brain.

The investigators looked into an airbase in western Afghanistan where, after receiving two incinerators in August 2012, personnel continued to burn its garbage in open pits.

The Shindand Airbase is home to 4,000 U.S. and Afghan military and civilian personnel. But while the incinerators paid for by the U.S government were operational by January 2013, the U.S-generated waste was burned openly until June 2013 and the Afghan military used the pits instead of the incinerators until October 2013. (Now the Afghan waste is hauled from the airbase.)

The incinerators were part of a $4.4 million solid waste management contract for Shindand.

This report is the fourth of its kind on the situation at various bases. In February 2014, the investigators visited Shindand and found that the incinerators meant for Afghan-use had still never been used. The watchdog recommends U.S. Central Command to look into some unanswered questions: Why did the U.S. military continue to use the burn pits after its incinerators were fully operational and why was Congress was never notified that they weren’t being used, which is required by law?

The investigators also want the U.S. to look into why the Afghans weren’t using the incinerators “we provided.” But Central Command has said it’s not its role to make the Afghan National Security Forces (ANSF) use them, though it would continue to encourage it. For the Afghans, the cost of running the incinerators is a deterrent even if there are serious health risks.

Currently there are lawsuits pending related to the open burn pits used in Iraq and Afghanistan and the resulting exposure to toxic fumes.