$1.5 million set aside to fight algae blooms in Silverberry

Pond one of five built too shallow

Edmonton is preparing to spend $1.5 million to address smell and algae concerns in Silverberry’s stormwater pond.

Drainage officials said it and four other ponds built by developers in new neighbourhoods were built too small and shallow. They quickly get overwhelmed with phosphorus and nitrogen, resulting in thick pond sludge and smelly odours.

But the city can’t charge the cost back to the developer. “The developer designed it. The city approved it and the developers build what was approved,” said Chris Ward, branch manager for utility operations. “We’re not going to accept this small a lake again. … Minimum one hectare lakes is really what we’re pushing for.”

The Silverberry project was one of several projects approved during a drainage capital budget adjustment Friday. Officials also approved work on Tweddle Place dry pond, Ekota dry pond and Tawa dry pond and associated pipe improvements at $26 million more than the $50 million originally budgeted.

They’ve decided to push back flood upgrades in other parts of the city to compensate.

“Haven’t we got our engineering right yet? It’s frustrating it’s taken so long to get this right,” said Coun. Ed Gibbons after the meeting. “I think of the (drainage) trouble we’re having in Mill Woods. Now we’ve got (fixes required) for new areas. Hopefully they’re getting better all the time.”

The Silverberry pond was built in 2001. The city started getting complaints about green pond scum and odours of plant decay as soon as they took it over from the developer, said Ward. They’ve tried everything they could think of to fix the problem, including mechanically removing the algae and treating the water with chemical products including $80,000 of PhosLok.

“A small, shallow lake will grow a lot of algae,” said Ward. “We’re trying a different approach with a pilot project (on this lake) saying, will a complete redesign and reconstruction of the lake work?”

The project will likely involve trenching the lake, then planting more natural plants along the banks to filter water and use up excess nutrients. The project will be done with a design-build-operate contract to ensure experienced engineers are involved the whole way through.

It’s a project mirrored on success Winnipeg experienced. Ward said what they learn from Silverberry will eventually be applied to other problematic ponds. Construction is scheduled for the fall of 2017.