A man convicted of three felony drunken-driving offenses in as many years was sentenced Thursday to 10 years at Montana State Prison.

Richard Michael Ziereis, 52, was sentenced by District Judge Susan Watters after pleading guilty in August to his sixth DUI. Ziereis was charged in March after a sheriff's deputy found the Helena man passed out in an idling pickup truck at the Lockwood School.

At the time of his arrest, Ziereis was on probation for two other felony DUI convictions. He had completed a state intensive alcohol treatment program eight months before his arrest.

Deputy County Attorney Victoria Callender said Thursday that Ziereis "threatens the safety of every member of this community and will continue to do so unless incarcerated." Ziereis has misdemeanor DUI convictions in 2001, 2003, and 2006. He was convicted of felony DUI in 2007 and again in 2008.

Callender asked the judge to sentence Ziereis as a persistent felony offender to 20 years at the state prison, with 10 years suspended, for the new DUI conviction. She also asked the judge to impose a 30-day jail sentence for a misdemeanor count of being a habitual traffic offender.

Ziereis' attorney, Mathew Stevenson, asked the judge to impose of state Department of Corrections sentence rather than a prison sentence. He said his client would do better in a community-based treatment program.

Ziereis told the judge that the last eight months in the county jail had been a "real eye-opener," and that he was recommitted to staying sober. He explained that before his last arrest he was drinking at a friend's house, was asked to leave and "drove around the corner" before going to sleep in the truck.

"I disagree that I'm a hazard to society," he said.

Ziereis' wife, Atalya, testified at the hearing and told the judge that her husband had suffered from severe depression the last three years. She described him as a hard worker and a "wonderful, kind human."

Watters said the three felony DUI convictions in the past three years convinced her that Ziereis cannot control his drinking. She told Ziereis he should not have been drinking alcohol at all in March.

Watters imposed a sentence of 15 years at the state prison, with five years suspended, for the felony DUI and a concurrent 30-day jail term for the misdemeanor.