SALEM – A Swampscott construction worker who was about to go on trial for trafficking drugs in Swampscott and Salem in 2007 opted to plea bargain his case and received five years in state prison.Mark McGrath, 28, of 258 Essex St., Swampscott, changed his plea to guilty Tuesday in Salem Superior Court rather than face a jury trial. He pleaded guilty to two counts of trafficking over 14 grams of OxyCodone and was sentenced to serve five years in state prison on each count by Judge Howard J. Whitehead.Although he was sentenced to a total of 10 mandatory years, he will only serve five of them because they will be served simultaneously instead of one after the other.OxyCodone is a derivative of Opium, which is used to treat severe chronic pain.Assistant District Attorney Robert B. Brennan said the two charges occurred in two different places, Swampscott and Salem.Shortly before 7 p.m. on Oct. 12, 2007, Swampscott police officer Michael Frayler stopped McGrath in a pick-up truck on Danvers Road, near Essex Street, for an expired registration sticker. When the officer approached the vehicle, he apparently smelled an odor of marijuana.He also observed a plastic bag between the driver’s seat and the console which contained 63 80-milligram tablets of OxyCodone, containing a total of 17 grams.McGrath then voluntarily told police he had additional pills and cash at his mother’s house in Salem and consented to the search, police said.Police went to 5 Bedford St. in Salem where they discovered 135 additional OxyCodone pills, containing 36 grams of Opium, along with $44,400 believed to be proceeds from sales in a safe in the house.McGrath confessed at the police station and admitted to police he is a “user” and that he buys the pills for $37 each and sells them on the street for $50 each, Brennan said.Initially McGrath had been charged with trafficking over 28 grams of OxyCodone on the second count, but as part of the plea concession the commonwealth agreed to reduce the charge to trafficking over 14 grams of OxyCodone. His confession to the charge spared him a minimum mandatory punishment of seven years in state prison.McGrath, who was represented by Attorney Bradford Elliot Keene, was indicted by an Essex County grand jury in May 2008 and has been free on bail since his arraignment.State Troopers William Pinkes and Jay Staudee also participated in the investigation.