WASHINGTON — Scott Pruitt, the chief of the Environmental Protection Agency, used one of his top aides last year essentially as a personal assistant, having her help him search for an apartment as well as to try to procure a used mattress from the Trump International Hotel, congressional transcripts show.

The aide, Millan Hupp, who serves as Mr. Pruitt’s scheduling director, also helped Mr. Pruitt obtain tickets to last year’s Rose Bowl football game. The details came from a partial transcript of an interview Ms. Hupp gave last month to congressional investigators, who are looking into Mr. Pruitt’s first-class travel, spending on security and other management decisions at the E.P.A.

The partial transcript was released Monday when Democrats on the House Oversight Committee wrote a letter to Representative Trey Gowdy, the Republican chairman, asking him to subpoena documents from the E.P.A. regarding Ms. Hupp’s real estate work.

At the time Ms. Hupp was apartment-hunting for Mr. Pruitt, the administrator was living in, but being urged to leave, a Capitol Hill condo he was renting from the wife of a lobbyist who had business before the E.P.A. Mr. Pruitt paid $50 a night when he was not traveling to live in the unit.