Work begins to cover mercury contaminated sediment in St. Clair River

Work is scheduled to begin this week to cap mercury contaminated sediment in the St. Clair River near Sarnia.

Article content

Dow Canada leads the work set to begin Monday to place an erosion resistant cover on sections of the river sediment, said Ontario’s Ministry of Environment, Conservation and Parks.

The work is expected to take up to seven weeks.

“We are very glad they are doing it,” said Kris Lee, the Canadian chairperson of the St. Clair River Binational Public Advisory Committee. “It has been a long time.”

The contamination is believed to have come from Dow Chemical’s Sarnia operation, which closed in 2009. A 2014 recommendation to the federal and provincial governments called for removing the sediment by hydraulic dredging at an estimated cost of about $28 million.

But an engineering consultant recommended in 2021 that the polluted sediment be capped, not removed.

Article content

“An extensive sampling campaign in 2019-2020 showed that mercury levels in the sediment have decreased significantly since the last samples were taken and the existing levels do not present a measurable risk to aquatic species,” the Ontario ministry said.

“To further reduce the risk of contaminated sediment moving downstream, project consultants recommended that an erosion resistant cover made up of double washed gravel be placed on areas with the highest mercury concentration,” according to the ministry.

Consultants found upstream sediment cleanup between 2001 and 2005, and along the shore of Dow Chemical’s former facility, helped cut mercury concentrations. Testing also determined the highest concentrations were buried in sediment.

Article content

Instead of hydraulic dredging, the consultant recommended adding “an erosion-resistant cover” of washed, fine gravel to three areas of river bottom with the highest mercury concentrations, Mike Moroney, St. Clair River remedial action plan co-ordinator with the St. Clair Region Conservation Authority, said.

This approach is expected to meet the project’s original goals and avoid risk that comes with dredging, like re-suspending contamination in the river.

A 2021 report identified three priority areas for the work: Near the TransAlta site (formerly Dow Canada) and Suncor’s site; Near property owned by Enbridge and Shell; Near Guthrie Park in St. Clair Township.

Dow will fund the work, Environment and Climate Change Canada has said.

Article content

The work was originally planned for fall 2023, but required permits weren’t secured in time, the federal ministry said previously.

Sediment management is one of the key remaining actions required for the St. Clair River to be de-listed as a Great Lakes Area of ​​Concern under the Canada-US Great Lakes Water Quality Agreement, the Ontario ministry said.

Several impairments identified in 1987 for the St. Clair River Area of ​​Concern have been removed and work continues to address the rest.

Removal of several has been “pending,” waiting for the sediment project to take place, Lee said.

“It seems to be closed on an issue,” she said. “We’ve been waiting for so long.”

[email protected]

Article content