Environmental Protection Agency Administrator Scott Pruitt answers reporters' questions during a briefing at the White House June 2, 2017 in Washington, DC.
Wahsington CNN  — 

The Environmental Protection Agency’s inspector general “plans to expand the scope” of its investigation into Administrator Scott Pruitt’s travel to Oklahoma to include all of his travel through September 30.

In a memo obtained by CNN, the inspector general said the objectives are to determine the “frequency, cost, and extent” of Pruitt’s travel, whether travel policies were followed, and whether those policies are sufficient to prevent waste, fraud, and abuse.

The expansion of the probe comes at the request of several members of Congress, the inspector general’s office told CNN.

The EPA confirmed to CNN that Pruitt used a private plane and military jet to travel for government duties instead of flying commercial on four occasions over the summer. The tab for taxpayers was nearly $60,000.

In August, the EPA watchdog said it launched a preliminary investigation into Pruitt’s travel after a hotline complaint and congressional requests which “expressed concerns” about frequent travel to Oklahoma – his home state – “at taxpayer expense.”

In late July, the watchdog group Environmental Integrity Project said travel records from a Freedom of Information Act request show that Pruitt spent 48 of 92 days in March, April and May traveling – including 43 days on trips that included stops in his home state of Oklahoma.

The EPA did not immediately respond to a request for comment.