 Bridge
pontoons could become a hazard
By Judie Steeves - Kelowna Capital News
Published: November 18, 2008 10:00 PM
Updated: November 19, 2008 12:00 AM Tom Tasaka is concerned about the prospect
of leaving the 12 old bridge pontoons floating on Okanagan Lake over the
winter, where heavy storms could set them adrift to damage other infrastructure
on the water.
He recalls a Jan. 14 storm last winter while his crews were working on construction
of the new William R. Bennett bridge adjacent to the 50-year-old Okanagan Lake
floating bridge, when high winds made it difficult to keep going.
As project manager for SNC-Lavalin for the bridge construction and operation,
including the demolition and disposition of the old bridge, Tasaka is still
waiting for permission from the environment ministry to sink the concrete pontoons
in Okanagan Lake.
However, the Canadian EarthCare Society has joined others in asking that such
a proposal go under the microscope of the ministry’s Environmental Assessment
Office now that all 12 of the pontoons are destined for disposal.
Tasaka said they had hoped the six that are still in good shape could be re-used
as a breakwater or similar project elsewhere on Okanagan Lake, but the City
of Kelowna considered that and rejected it, as did other jurisdictions.
“We considered them an asset that could be re-used, but now there are
no takers, so we’re looking to sink them all,” explained Tasaka.
That means the disposal has a larger footprint on the bottom of Okanagan Lake,
which could trigger a review by the EAO. That’s under consideration right
now.
However, Tasaka said the pontoons weigh more than 3,000 tonnes each and couldn’t
possibly be lifted out of the water, although they could be floated elsewhere
along the lake.
The only possible alternative to sinking would be for six of them to be floated
to the graving docks where the new bridge’s pontoons were constructed,
then dried and broken up for re-use in new concrete, but Tasaka noted there’s
no shortage of aggregate in the Okanagan.
Besides, he said their studies have shown there would be harmful impacts to
the environment and a waste of energy from breaking them up too.
And, six of them are too large to go into the graving dock.
To concerns expressed by groups such as EarthCare, he said the areas identified
for sinking them are between 150 and 230 metres deep, and a good distance from
any water intakes, which are at about 30 metres in depth anyway.
There’s no fish habitat at that depth and tests of the sediments have
shown the content is within environment ministry criteria, he said.
Detailed modelling of the sediment plume that would result from sinking them
in the lake has been doned.
And he said they have taken samples from the cleaned pontoons and there’s
nothing in them that would be harmful to drinking water.
As well, he noted they’ve been in Okanagan Lake for 50 years and haven’t
created any problems.
“We’re not talking about sinking the steel or asphalt, just the
concrete pontoons,” he said.
“We’ve done all our practical work.”
Tasaka also proposed sinking one pontoon south of the bridge, where it would
be farthest from the nearest water intake, and measuring the plume of sediment
to ensure the others wouldn’t create any problems near intakes.
The environment ministry didn’t expect to make a decision this week on
whether to send the proposed disposal through the Environmental Assessment
Office process.
jsteeves@kelownacapnews.com
<< back
|
