USA TODAY NETWORK Dennis Wagner and Craig Harris, The Arizona Republic

WINDOW ROCK, Ariz. — A Navajo Nation housing agency that has struggled for years to provide dwellings for tribal members, and was the subject of a recent Arizona Republic investigation, is under scrutiny again by the federal Department of Housing and Urban Development.

HUD officials, including a deputy administrator and federal grants specialists, visited the reservation for a week in March after sending a letter to Navajo Housing Authority officials seeking information on construction projects that had failed or were severely flawed.

The Republic in a December 2016 series found the NHA, which has received more than $1.66 billion in federal funds since 1998, built fewer than 300 new residences in the past five years. Just as alarming, however, were revelations of more than $100 million in waste in projects that were built. Among the glaring failures: 36 igloo-shaped townhouses in Tolani Lake, built for $7 million over a decade ago, were never occupied and are decaying.

As the new federal inquiry was being launched, The Republic obtained records of other questionable expenditures from the NHA. Among them:

The housing authority reported that it paid $54.9 million during fiscal 2016 to modernize 50 dwellings — an average of nearly $1.1 million per unit as calculated by The Republic.

The agency awarded a contract of more than $76 million to supply and install manufactured houses. If all 170 are completed, the price works out to nearly $450,000 each. That includes no real-estate expense, because the dwellings are being placed on tribal trust lands.

The NHA since 2012 has paid $3.9 million to Swaback Partners, a Scottsdale consulting company, to survey the reservation and develop new housing strategies and plans. The authority has identified no residential units that resulted from those plans.

“HUD’s staff will seek to fulfill its responsibilities to the public by ensuring our funding is being used in compliance with our required policies and in a timely and appropriate manner,” HUD spokesman Hang Liu said of the recent federal investigation on the reservation. “We will then use the information we gather to determine if any corrective actions may be necessary in the future.”

HUD officials indicated they intended to examine at least 10 failed or questionable housing projects, including the demolition of 90 unfinished homes in South Shiprock, N.M., and the construction of a women’s shelter in Kayenta that sat unopened for years.

The HUD team presented its findings to NHA officials on March 17. Liu declined The Republic‘s request to attend that meeting. HUD eventually will produce a final monitoring report on its findings that may include corrective action by the NHA.

Accounting for the spending