Wrapping up a two-year investigation of for-profit colleges, Senator Tom Harkin will issue a final report on Monday — a voluminous, hard-hitting indictment of almost every aspect of the industry, filled with troubling statistics and anecdotes drawn from internal documents of the 30 companies investigated.

According to the report, which was posted online in advance, taxpayers spent $32 billion in the most recent year on companies that operate for-profit colleges, but the majority of students they enroll leave without a degree, half of those within four months.

“In this report, you will find overwhelming documentation of exorbitant tuition, aggressive recruiting practices, abysmal student outcomes, taxpayer dollars spent on marketing and pocketed as profit, and regulatory evasion and manipulation,” Mr. Harkin, an Iowa Democrat who is chairman of the Senate Health, Education, Labor and Pensions Committee, said in a statement on Sunday. “These practices are not the exception — they are the norm. They are systemic throughout the industry, with very few individual exceptions.”

In a statement on Sunday, the Association of Private Sector Colleges and Universities, the leading trade group of for-profit colleges, called the report “the result of a flawed process that has unfairly targeted private-sector schools and their students.”