As far back as 1992, Save Our Seine expressed concern about a former shingle manufacturing
facility in the St Boniface area. Sludge had been seen for years on the surface of the river near the facility. During a tree planting event on the banks near the site, SOS and volunteers played trial and error digging holes until they found one that didn’t hit old shingles. Those trees eventually withered and died.

According to several investigations undertaken as far back as 1995, there was confirmed shallow
soil and groundwater contamination along with tarry material present on the site, beneath the sediment under the river as well as contamination of the river itself. This was a confirmation
of SOS’s worst fears.

SOS worked for nearly 15 years attempting to keep this site on the front burner of politicians' and
Manitoba Conservation's priority list, and remediation was finally announced in 2008 and carried out by the owner of the land, Honeywell, in 2009. This project was one of largest decontamination efforts ever undertaken in Manitoba. Manitoba Conservation had to develop a protocol specifically for the project for dealing with each level of contamination.

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The remediation involved the excavation and disposal of contaminated soil and sediment, then backfilling with clean materials. This became complicated because the coal tar migrated under the riverbed. Over a period of nearly 100 years, the coal tar was able to seep under the river between the river bottom and a layer of good old Manitoba clay. Up to 15% of the contaminants actually migrated all the way under the river and up the west riverbank. The contamination zone stretched from the factory site on the east bank across the river and nearly 20 meters into the west bank.

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Since the contaminated zone stretched under the river and onto the far bank, diversion and excavation of the river bottom itself was necessary, taking place in September 2009. Canoeists were directed to a portage and a “fish rescue” was conducted when the channel was capped. Within a channel of a few hundred meters, 20 fish were found, comprised of 9 species including jack, bass, bullhead, crappy, and crayfish. These fish were returned to the diverted river and were free to roam the temporary channel and reconnect with the Seine.