Almost $70,000 later and it's back to square one in the search for an underground source of diesel fuel that's contaminating the subsurface in a downtown area.

Brian Levia of the Department of the Environment said this morning everybody is somewhat mystified after a drill program conducted last week failed to provide any clues regarding the source of the leaking fuel.

Levia said diesel fuel home heating fuel is continuing to seep into the sump of the Optometrists Building at the corner of Lambert Street and Second Avenue.

Underground tanks that supplied the building were pressure-tested and eventually dug up to verify they were sound and not the source the fuel.

When crews removed the tanks in mid-April, they dug down a further metre. Suddenly there was gush of diesel fuel pouring into the hole by the bucket full, in the amount of 800 litres (174 gallons) in two hours before they had fill the hole back in to protect the integrity of the footings.

So far, with the fuel from the hole and the fuel that's been captured from the sump, officials have collected some 4,000 litres (880 gallons), or the equivalent of about 3 1/ 2 tank fulls of home heating fuel.

The leak was detected in early April from an area resident who reported a oil sheen on the Yukon River. The source was determined to be the Lambert Street storm drain, and subsequently the sump that collects excess groundwater flow around the Optometrists Building.

Levia said an examination of fuel records from neighbouring buildings has also turned up no leads in the investigation.

The drill that was brought in to do the work is a specialized piece of equipment with advanced sensors that detect fuel and other unnatural substances.

At a cost of $67,800, 12 holes were drilled around the building, but none of them turned up any fuel.

He said one of the drill holes was within two metres of where the tanks were buried.

'It's got everybody baffled; the consultant, the drilling company nobody expected to get nothing,' said Levia.

He said the plan now is to dig the hole again where the tanks were and trace the fuel back from there.

They have yet to set a date to start the next phase of the search, he said, though it remains a high priority.

The reclamation work on and around to the Whitehorse Esso property, which is kitty-corner to the Optometrists Building, was unrelated to the fuel leak detected in April.

Levia said none of the extensive excavation work carried out by Imperial Oil turned up any hint of where the fuel might be coming from.

Labs have confirmed the fuel is no more than a year old.