The source of heating oil that put the Auke Bay Wastewater Treatment Plant out of commission more than a week ago is still unknown.
A heating oil tank at a nearby apartment complex was originally suspected, but it did not prove to be the culprit. The Department of Environmental Conservation then theorized the oil bled from lines leading to or from the apartment complex on Glacier Highway near the Auke Bay Post Office.
But when the lines were pressurized Saturday, no leaks could be found, said Scot Tiernan of DEC's Division of Spill Prevention and Response.
``So we are still dealing with a mystery, and it's driving us nuts,'' Tiernan said.
A ventilator has been installed at the treatment plant to speed dissipation of oil, and new bacteria needed for the plant's waste processing system is en route from the Lower 48. The oil killed existing bacteria used to process waste.
More than 60 yards of contaminated soil were removed from the site, and the excavated area has now been filled back in, Tiernan said.
``They put in two large culverts up to the surface to collect oil, but there is nothing coming in,'' he said. ``(The source of oil) seems to be gone.''
All removed soil is being transported to United Soil Recycling in Juneau for treatment.
The Auke Bay treatment plant, which usually handles 70,000 to 100,000 gallons of wastewater a day, has been shut down due to its inability to treat sewage. It will not operate until the source of the oil has been found and levels of poisonous oil within the plant's sludge allow re-seeding with beneficial microbes.
In the meantime, the city continues to let wastewater that is not fully treated flow into Auke Bay.
The city is removing inactive sludge from the plant and burning it in its sludge incinerator.