Arizona can save $30 million to $73 million a year by going to an "earned release" system for nonviolent offenders, a new study says.

The Grand Canyon Institute, a Phoenix-based organization that describes itself as "centrist," says in the report released this week that the state's requirement that nonviolent offenders serve at least 85 percent of their sentences costs taxpayers money.

At the same time, the report says, it keeps many drug-addicted offenders from getting the treatment they need, so they simply return to prison time after time.

“Our prisons can be a revolving door," says former Republican state Rep. Bill Konopnicki, a member of the Grand Canyon Institute's board. "Last year 19,055 people left the Arizona Department of Corrections and another 18,759 people replaced them. At least three in four have significant substance abuse issues, yet last year only 1,810 received treatment. It’s no wonder that repeat offenders make up seven out of every 10 inmates.”

Study author Dave Wells, a research fellow with the institute, is quoted in a press release as saying that the Arizona Legislature's Safe Communities Act of 2008 has allowed county probation departments to offer incentives for reduced sentences, and it has saved money.

"Under the law probationers earn 20 days off their sentence for every month they meet all their obligations, which can include drug testing," the institute's release said. "The number of individuals with probations revoked and sent to prison has dropped dramatically as a consequence. Reductions in Maricopa County alone now save the state $27 million annually over 2008."