PORTLAND, Ore. -- A former mailman with the U.S. Postal Service will serve 18 months in prison for dealing marijuana along his mail route, a judge ruled on Tuesday.

Richard Berkan, 48, pleaded guilty earlier this year to distributing pot while on his mail route in the Cedar Mill area of Washington County, local station KPTV reported.

As part of Berkan's sentence, almost $3,000 worth of drug proceeds will be forfeited.

The investigation began in 2006 when the U.S. Postal Service received a citizen complaint that a mailman was offering marijuana for sale.

Investigators said they had a significant break in the case when Lake Oswego police arrested a 19-year-old who had been buying marijuana from Berkan. The teen said he had been purchasing pot from Berkan since he was in high school.

Authorities later searched Berkan's home and found 47 marijuana plants and 9 pounds of marijuana.

After working for the U.S. Postal Service for almost 15 years, Berkan resigned in April as part of his agreement with the prosecution.

"Postal carriers are trusted by the public to be honest and upstanding in carrying out their duties," said Karin Immergut, United States Attorney for the District of Oregon. "In this case, not only did the defendant violate that public trust by dealing drugs on his mail route, but he also sold drugs to a person under 21 years of age."