Enbridge Pipelines has been fined $70,000 for contravening its Environment Ministry Certificate of Approval at its facility on Plank Rd. in Sarnia.
A ministry site inspection in June 2013 found that contaminated water from five of ten excavation pits was being pumped to a drainage ditch network.
The network is part of a system that collects storm water in ponds and intermittently discharges it to the Cole Drain that flows to the St. Clair River.
The Environment Ministry says Enbridge continued pumping excavation water to the drainage ditch network until the end of July 2013.
Sampling of the water later showed elevated total suspended solids, cadmium and chromium.
The company pleaded guilty and was fined $70,000 under the Ontario Water Resources Act plus a victim fine surcharge of $17,500.
Enbridge was given six months to pay the fine.