(CNN) Newly released documents show how the Environmental Protection Agency justified several expensive charter flights for Administrator Scott Pruitt -- including a $14,000 bill for a business trip around his home state.

The documents include multiple memorandums from EPA attorneys to Pruitt's office justifying the charter flights in June, July and August of 2017.

In late August, the EPA inspector general announced it would investigate Pruitt's travel practices, including his frequent trips to Oklahoma, where he has a home and, until last February, served as state attorney general.

The $14,435 flights took him from his hometown of Tulsa to Guymon, Oklahoma, a small farming community about 330 miles away. After a meeting with landowners, the plane shuttled him to Oklahoma City, the state capital, where he met with a newspaper editorial board and state officials. (Days later, The Oklahoman published an editorial, "Citizens should welcome EPA changes," defending his controversial moves at the agency.)

The travel documents, uncovered by the watchdog group Environmental Integrity Project and shared with CNN, show the air travel had been approved the day before by the EPA's acting general counsel, on the grounds that it was for official business and "Guymon is not accessible through commercial means."

Except by car.

Guymon is about a five-hour drive west from Tulsa, and the trip to Oklahoma City is about a four-and-a-half-hour drive southeast.

According to the documents, "the time constraints on the Administrator's schedule did not allow the Administrator to travel by ground transportation."

Pruitt did decide to make other legs of this Oklahoma visit by car.

He was driven between Tulsa and Oklahoma City -- a one-hour, 45-minute trip each way -- four times over three days, his travel itinerary shows.

The documents suggest he made the roughly 100-mile drive so that he could stay at his home instead of a hotel.

"There is no lodging costs to EPA at all for this trip," a travel itinerary notes.

Reached for comment, EPA spokeswoman Liz Bowman said: "With respect to visiting Guymon, it was an important stop on our WOTUS [Waters of the United States] tour where we were able to hear comments from people who have been directly affected by the rule, whose voices have been disregarded in the rulemaking process. By visiting with government officials and citizens, we treated Oklahoma exactly like we did North Dakota, Minnesota, Indiana and every other state we visited during the tour."

Waters of the United States is a controversial Obama-era EPA regulation that the agency under Pruitt is rescinding and rewriting. Critics say it was overly broad in classifying waterways that are subject to federal rules, while supporters see it as a necessary protection, for example, preventing fertilizer runoff from tainting streams and drinking water.

It was Pruitt's frequent visits to his home state that drew complaints to the inspector general. Since beginning the probe in August, the IG has twice expanded its scope, which now encompasses all of Pruitt's 2017 taxpayer-funded travel.

The Environmental Integrity Project, which has been critical of Pruitt, last summer analyzed his schedules and found he spent about half of his days in or traveling to Oklahoma during his first three months as administrator.

Scrutiny of Pruitt's habit of flying first class has also been mounting. The Environmental Integrity Project extrapolated from the price of his tickets that many of his trips were in the first-class cabin.

"I checked flights to Tulsa tonight from DC flying out tomorrow and returning Monday (at a reasonable hour) and round-trip economy flights were available for $615 on very short notice," Environmental Integrity Project director Eric Schaeffer said. "The government gets a preferred rate, so I wouldn't expect them to pay more than I could find on Kayak."

At least one of Pruitt's flights was for a June meeting in Tulsa with a glass and metal company called Ardagh, based in Sapulpa, Oklahoma. The itinerary for this trip indicates that the company was having an "issue" in Indiana it wanted to discuss with the administrator.

Documents show that in the previous year, January 8, 2016, the Obama EPA issued a detailed request for information from Ardagh to determine if emissions from its facility in Winchester, Indiana, put it in violation of the Clean Air Act. It is unclear what the "issue" was that the company wanted to discuss with Pruitt.

The company did not immediately respond to CNN's request Friday for comment.

The meeting raises concerns for Schaeffer because EPA data compiled by the Environmental Integrity Project showed the penalties levied against corporate polluters have dropped since Pruitt took office.

Information about ticket prices for Pruitt's security staff was not made available as part of the Environmental Integrity Project's records request, Schaeffer said.

The records also shed light on a charter flight Pruitt took in August, a trip for which the agency acknowledged commercial options were available.

Pruitt flew from Denver to Durango, Colorado, for an event at the Gold King Mine, where a 2015 EPA cleanup project led to a massive wastewater spill that turned a nearby river orange.

The commercial flight he and his team were scheduled to take was delayed, and Pruitt's team began looking for other options so he would not miss the event. The governor's office offered Pruitt a seat on its plane, but Pruitt turned that down because he needed more than one seat.

The documents obtained by the Environmental Integrity Project show there was another commercial flight that Pruitt could have taken. The EPA's top attorney, acting general counsel Kevin Minoli, wrote that the airline "may have gone as far as to reserve the seat in case we determined it would meet the travel needs and requirements."

However, the flight lacked an additional seat for Pruitt's special agent. The EPA eventually decided to charter a flight, at a cost of more than $5,000, the documents show.