BOSTON -- Five people were arrested last night and 15 kilograms of cocaine seized as part of a six-month investigation by State Police assigned to Attorney General Tom Reilly's Office with assistance from Boston Police Department and the Drug Enforcement Administration (DEA).State Police assigned to the Attorney General's Office with assistance from Boston Police and the DEA executed a search warrant last night at a residence at 18 Monson Street in Mattapan. Five people, four men and one woman, were arrested and 15 kilograms of cocaine were seized. The arrests and seizure follow a six-month investigation utilizing both electronic and physical surveillance that focused on a major cocaine trafficking operation in and around Boston. The people arrested last night were allegedly running a wholesale and retail distribution operation in which they allegedly sold both large quantities of cocaine and also broke it down into smaller amounts. Over the last few days State Police developed information about a large shipment being moved by car from Georgia coming north. Today State Police investigators tracked that shipment to a location in Mattapan. It was moved from there to the location at 18 Monson Street late yesterday afternoon where five individuals were placed under arrest. A search of the residence yielded 13 individual kilogram bricks of cocaine concealed in a compartment underneath a floor in the second floor of house. Another kilogram was found in a bedroom, and the 15th kilogram, which was being "cooked" into crack cocaine, was found in the cellar. The cocaine seized today has an estimated street value of more than $1 million. State Police also seized a handgun at the first location in Mattapan. The five people are scheduled to be arraigned this morning in Dorchester District Court on trafficking and conspiracy charges, and all face mandatory 15-year sentences. The investigation is ongoing.