After $200,000 in expenses, the territorial Department of Environment is shelving its 18-month search for the source of a mysterious underground fuel leak.

Brian Levia, manager of monitoring and inspections, explained Wednesday the decision to remove the treatment equipment from the Optomitrists Building came six months after the last trace of heating fuel was detected in the building's sump.

The monthly cost of maintaining the equipment was approximately $2,500. The equipment was removed at the end of October.

'The treatment system part of it is closed but the investigation remains open,' Levia said. 'We will still follow up on anything we hear but we have not heard from anybody for about six months.'

The investigation began when an oil sheen was reported floating on the Yukon River in April 2005.

Federal and Yukon government investigators traced the source of the sheen back to the Lambert Street storm drain, and subsequently the sump inside the Optomitrists Building.

Upon excavation of the underground fuel tank that supplied the building, it was determined the tank was not the source.

During the excavation, however, approximately 800 litres of heating fuel gushed into the hole.

Over the course of the treatment program, about 4,000 litres were collected from the initial gush and the ongoing treatment system installed in the building's sump.

Despite a search of fuel records from buildings in the area, a $70,000-drill program using a special mobile rig from B.C. and an inspection of fuel tanks in the downtown area, government officials were unable to locate the source.

Laboratory analysis showed the fuel was the same type as that sold by North 60 and Summit Fuels at the time, and not that of Great Northern Oil nor Petro-Canada.

The analysis also indicated the fuel was no more than a year old.