Time, wind and sunlight do most of the work at Whitehorse's new sewage lagoon, the Livingstone Trail Environmental Control Facility.

"The only thing we add to the system is a biological enzyme," says Utilities Supervisor Jim McLeod. "It eats the sludge and keeps the water temperature up high enough to keep the system alive through the winter."

The City is generally pleased with the operation of the facility, opened in 1996 to replace a system Whitehorse had long outgrown. Tests show the system is meeting or exceeding all the requirements of its water licence, McLeod says.

For example, the water licence says fecal coliform levels in effluent from the system may not exceed 2000 counts per 100 millilitres. Fecal coliform are an indication of contamination.

McLeod says tests of the new system have found fecal coliform counts ranging from less than 3 per 100 millilitres to a high of 240. The old system would discharge over 100,000 counts per 100 millilitres.

The trick is to give natural processes time to do their work. The Livingstone Trail facility is designed to hold the sewage for at least 360 days at optimum capacity. During that time, the wind stirs the holding cells and puts oxygen into the system, helping microbes and natural chemical processes to break down harmful components of the sewage. Added enzymes accelerate the process and keep it perking along, winter and summer.

Currently, sewage spends much longer than 360 days in the system. Due to the facility's large storage capacity, no effluent has been released since it opened over a year and a half ago.

The Livingstone Trail facility includes two primary cells, four secondary cells, and a long-term storage area. The primary cells can fill to a depth of 6.2 metres and the secondary cells to a depth of 2.3 metres.

The long-term storage area, a wetland three kilometres long and two kilometres wide, can fill to a depth of six metres. After more than a year and a half of operation, McLeod says, the primary and secondary cells have filled and the long-term storage area is just beginning to fill.

The system has so much holding capacity that City officials don't expect to have to discharge effluent until 1999.

The original plan, set out in the City's water licence, was to discharge the treated effluent into the Yukon River, downstream from Whitehorse. However, the City has come up with a new plan, says McLeod.

The City has applied to the Yukon Territory Water Board to obtain an additional Class A water licence for a trial discharge of up to two million cubic metres of fully treated effluent into a pothole lake near the Livingstone Trail facility. The discharge would gradually seep into the groundwater, along with other water from the lake, and very slowly make its way to the river.

"Our hope is not to have any direct discharge into the river with this pothole lake," says McLeod.

The pothole lake chosen for the trial discharge is a geological oddity, he says. It lies 16 metres below the level of the surrounding lakes and less than a decimetre above the level of the river itself, so there is no chance that it will overflow into surrounding surface water.

The trial discharge will be closely monitored to make sure it does no harm to the lake or the environment around it. If the test works, it will remove the need to build a discharge facility in the river. That not only saves money, McLeod says, but also reduces disturbance to fish habitat and eliminates the risk of damage to the outfall system from ice or boats.

And it means an even longer delay before the product of Whitehorse's sewage system makes its way to the Yukon River.

For more information about sewage treatment in Whitehorse, contact the City of Whitehorse Engineering Department at 668-8305.