According to Sopko, the Department of Defense worked to build the compressed natural-gas filling station from 2011 to 2015. He says the task force that was working to build the gas station, the Task Force for Business and Stability Operations (TFBSO), was created in 2009 to resuscitate Afghanistan's economy. That task force is now obsolete.

"The Department of Defense claims that it is unable to provide an explanation for the high cost of the project or to answer any other questions concerning its planning, implementation, or outcome," Sopko wrote.

The report notes that compressed natural gas is 50 percent cheaper and burns cleaner than regular Afghanistan gasoline.

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