Forty years after Dow spilled perchloroethylene, the final part of the clean up is underway

Cathy Dobson/The Independent

The last of the St. Clair River sediment contaminated in 1985 by the infamous “Blob” is being covered with a layer of aggregate this week.

When crews spread 15 to 25 centimetres of fine gravel over three areas at the bottom of the river Tuesday, cleanup of that particular environmental catastrophe will come to a close after 40 years.
“It’s wonderful really, a great news story,” says Terry Burrell, a Sarnia city councillor and vice-chair of the St. Clair River Bi-national Public Advisory Committee (BPAC).

BPAC is just one of many players including government, industry and citizen groups that have worked for four decades to dramatically improve water quality in the river and reinstate it as a place where aquatic life thrives and swimming is safe.

In August 1985, Dow Chemical Inc. spilled 11,000 litres of perchloroethylene, a carcinogenic dry cleaning chemical, into the river. It soaked up a toxic cocktail from years of chemical spills in the river from companies like Dow located along the shoreline.

When divers took a closer look, they found a dark tarry mass approximately the size of a basketball court lying in the river bottom. The international media infamously coined it “The Blob.”
It was a black eye on Sarnia-Lambton for years, but it also alerted government and industry leaders to how vulnerable the river was after a long history of industrial and urban development along both sides.

And The Blob generated an unprecedented effort to do better.

Dow – which closed in 2009 and moved operations to Michigan – cleaned up a large portion of The Blob in the 1980s. Efforts to improve water quality have continued for decades, including the removal of over 13,000 cubic meters of contaminated sediment in 2005.

Government standards and regulations to stop industrial contaminants into the river tightened. Many steel retaining walls along the shoreline were replaced by armor stone. Municipalities worked diligently to stop raw sewage from dumping into the river during heavy rain, and scientists began regularly testing for contaminated sediment.

By 2015, all but three major patches of contaminated sediment were cleaned up.

In January and February, an erosion resistant cover will be placed over those areas located near the TransAlta site (formerly Dow Chemical), farther downriver near property owned by Enbridge and Shell, and near Guthrie Park in St. Clair Township.

“Once this is done, all major areas of contamination will be remediated,” said Burrell. “These are the last big items in terms of industry.”

Burrell said Dow should be lauded for taking a lead on the final clean-up and paying the $1.5 million bill.
“The real hero in this is Dow in that they’ve taken responsibility,” he said. “And they’ve come back to take care of this final (remediation).

“It’s a real plus to them.”

The collaborative effort of federal, provincial and state reps, working with Indigenous people, groups like BPAC, and municipalities, has resulted in a much healthier river, Burrell said.

“Everybody has worked together on making our river better. There are a few outstanding concerns but these three are the last big ones.”

Crews began the current capping project in November and expect to finish within seven weeks, said Gary Wheeler with the Ministry of Environment, Conservation and Parks.

Originally, 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.

“An extensive sampling campaign in 2019-2020 showed that mercury levels in the sediment have decreased significantly since the previous samples taken in 2014 and the existing levels do not present a measurable risk to aquatic species,” said Wheeler in a written statement.

Project consultants recommended an erosion-resistant cover of double washed gravel placed on the three areas rather than run the risk of stirring up the contaminants with dredging.

Contaminated sediment has accumulated over time in the three priority areas where barriers like large docks are present or where the flow rate of the river decreased, according to Wheeler.

An erosion resistant cover is expected to keep all contaminants in place.

Following remediation, the ministry will continue to assess aquatic species for contaminants and ensure the health of the river, Wheeler added.

A DEEPER DIVE:

• The St. Clair River was designated as an Area of Concern (AOC) in 1987 under the Canada-United States Great Lakes Water Quality Agreement.
• 14 Beneficial Use Impairments (BUIs) that indicate pollution is impacting local fish, habitat quality and water quality were originally listed for the St. Clair River following the discovery of The Blob. All 14 must be addressed before the river can be delisted as an Area of Concern.
• Five BUIs remain to be addressed in the St. Clair River. This week’s capping will advance the status of two of the BUIs and the management of mercury-contaminated sediment.
• Therefore, the St. Clair River continues to be an Area of Concern.

Source: St. Clair River Bi-national Public Advisory Committee