The source of an underground oil leak continues to baffle staff at the territorial Department of Environment, says its manager of monitoring and inspections.

Brian Levia said his office will continue to explore any information that arises concerning the leak. However, the department does not have plans for more capital expenditures to search for the source.

The government has spent $180,000 over the last year trying to pinpoint where the furnace oil is coming from, he confirmed.

Tens of thousands of dollars were spent, for example, to rent a specialized drill from Vancouver to come and punch several small bore holes around the Optometrists Building on Second Avenue in an attempt to determine the direction the diesel fuel was coming from.

Results, however, were inconclusive.

While there are no similar plans for capital expenditures, the department is by no means closing the file, Levia said.

There have been approximately 4,000 litres collected at the Optometrists Building since the leak was detected in April 2005.

But it has diminished to just a trickle in recent months, amounting to less than a litre since Christmas, Levia explained.

The leak was reported last spring by an area resident who noticed an oil sheen polluting the Yukon River.

The source was traced back through the storm sewer on Lambert Street, and then to the Optometrists Building.

Excavation of the building's underground fuel tanks eliminated those tanks as the source. During the excavation, crews encountered a sudden gush of about 800 litres of furnace oil into the hole.

The investigation to date has included checking fuel records for businesses and homes in the area to search for abnormalities in consumption.

A mechanism was installed to capture the fuel leaking into the sump of the Optometrists Building, to prevent any further escape into the storm sewer and the Yukon River.

Levia said the reduced flow of the underground fuel suggests it is not coming from an ongoing source, but is likely linked to a one-time event.

Laboratory tests showed the fuel was less than a year old.

'We consider it to be the same product,' Levia said of the diesel fuel that continues to seep into the sump.

'We will be doing another round of analysis to confirm that, but right now we are considering it to be the same product.'