WASHINGTON -- The Department of Defense spent almost $43 million to build a compressed natural gas station in Afghanistan that would have cost up to $500,000 anywhere else and which may no longer even be operational, a congressional watchdog said on Monday.

"Even considering security costs associated with construction and operation in Afghanistan, this level of expenditure appears gratuitous and extreme," wrote John F. Sopko, the special inspector general for Afghanistan reconstruction, in SIGAR's just-released report on the Pentagon-funded station.

Sopko cited figures from the International Energy Association and the Pakistani government to say it should have cost between $200,000 and $500,000 to build a compressed natural gas station, even in an underdeveloped and relatively dangerous country.

The Pentagon's Task Force for Business and Stability Operations, which had an $822 million budget for projects in Afghanistan between 2010 and 2014, contracted an Afghan company to build the station in 2011 to demonstrate the potential of CNG stations to investors. That contract was for $3 million, the SIGAR report noted -- but the cost to build and supervise the station ended up soaring to $42.7 million by 2014, with $30 million going to overhead costs, according to the task force's own assessment.

The station opened in May 2012, and the task force planned to license it to a private firm willing to build a second CNG station, according to task force documents SIGAR cited. An Afghan firm did take over the station in May 2014, but its license expired in November 2014, and neither the watchdog nor the Defense Department could confirm that it is still operating, the inspector general said.

The report blasts the Pentagon for claiming that it can no longer answer questions about the task force that financed the station's construction.

The Office of the Secretary of Defense could not respond to SIGAR's queries or assess task force documents because the entity was shut down in March, wrote Brian McKeon, the Pentagon's principal deputy undersecretary of defense for policy, in letters attached to the report. Pentagon officials would have been happy to help locate former task force officials and sort through documents about its activities, but SIGAR investigators did not take up that offer, McKeon wrote, and that was the most the Defense Department could do.

Lt. Col. Joe Sowers, a Pentagon spokesman, told HuffPost in an email on Monday that the department had established a reading room to help SIGAR and highlighted the offer to contact the former officials.

Sopko and his allies on the Hill are not satisfied with that reasoning.

"One of the most troubling aspects of this project is that 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 in an Oct. 22 letter to Defense Secretary Ash Carter regarding his report.

Sen. Claire McCaskill (D-Mo.), a senior member of the Senate Armed Services Committee and the ranking member of its investigations subcommittee, sent her own letter to Carter on Nov. 2.

"I am particularly troubled by [the watchdog's] account of its difficulty in obtaining information regarding the CNG facility," McCaskill wrote. She asked Carter to tell her staff who at the Pentagon is now responsible for the shuttered task force's projects, which together cost U.S. taxpayers more than $800 million.

Theres few things in this job that literally make my jaw drop. But of all the examples of wasteful projects in Iraq and Afghanistan that the Pentagon began prior to our wartime contracting reforms, this genuinely shocked me," McCaskill said in a statement to The Huffington Post. "Its hard to imagine a more outrageous waste of money than building an alternative fuel station in a war-torn country that costs more than 8,000 percent more than it should, and is too dangerous for a watchdog to verify whether it is even operational.

The controversy surrounding the task force -- once praised as essential for future stability -- may become one of the most prominent battles in the fight to expose U.S. government waste in Afghanistan. While Pentagon officials have cooperated on other audits, they seem especially reluctant to allow access to information about the task force, SIGAR said. "Experience indicates that [the Defense Department's] repeated promises of access to [task force] files are more pretense than promise," the report stated.

The Pentagon disputes that view. "We welcome continued review of [the task force] by SIGAR," Sowers said.

As American forces come home and the Taliban insurgency against the U.S.-backed government in Afghanistan gains strength, the U.S. has found it increasingly difficult to monitor the success of its reconstruction efforts there. Sopko previously warned that President Barack Obama 's planned troop drawdown would diminish that ability further. But Obama decided in mid-October to abandon his plan to slash the U.S. troop presence in Afghanistan by the end of his presidency, and 5,500 American soldiers will remain in the country in 2017, after the president leaves office.

UPDATE: Feb. 3 -- The $43 million figure SIGAR initially quoted has now become controversial. Vestige Consulting, a firm that assessed the Pentagon-backed task force in 2014, told the Senate Armed Services Committee in late January that it believed SIGAR had exaggerated the number. It said too much of the task force's other overhead costs were assigned to the filling station, artificially pumping up its cost, according to The Washington Post's Fact Checker . The total cost of the station was under $10 million, Vestige argued.

SIGAR told the Post this week that it believes the $43 million figure remains "the best available number" and that the watchdog would issue an updated report if it received evidence suggesting otherwise.

The Post said it would not, at present, rate the accuracy of the SIGAR claim, which is now being cited by a number of top presidential candidates. "Theres enough blame to go around -- Pentagon officials who gave figures to a consultant without enough due diligence, SIGAR officials eager for a flashy headline, and an overly credulous news media -- that we will leave this unrated. But politicians are on notice that the story of the $43 million gas station should be treated with deep skepticism," Fact Checker columnist Glenn Kessler wrote.

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