Suncor Energy, Canada's largest integrated oil company, said it was treating water from a roadside ditch near its refinery in Sarnia, Ontario, after the chemical benzene was found in two water samples.

The contaminated water samples, taken during a recent storm, were drawn from the ditch located behind the refinery, near an existing remediation site that was established in 2006 after benzene was found in the soil.

Suncor said the sampling was done to better understand the potential impact surface water run-off has on ditch water during prolonged rain.

Company spokeswoman Nicole Fisher said the company closed the ditch sluice gate and installed clay berms around the area to contain the contaminated water. It used pumps and vacuum trucks to help process the water through the refinery's wastewater treatment facility.

The company is continuing to monitor water in the ditch.

Production at the 85,000 barrel per day Sarnia refinery has not been affected.

"Samples drawn from ditch water upstream and downstream of the remediation site did not indicate any benzene levels, so there was no contaminated water that was running off the Suncor site," Fisher said in an email.

Benzene is a highly flammable, organic chemical that forms a natural part of crude oil.

People who drink water with exposure to benzene in excess of the maximum contaminant level of 0.005 milligram per liter for many years may have an increased risk of developing cancer, according to the U.S. Environmental Protection Agency website.

Fisher said benzene levels in the two affected water samples did not exceed levels described in Ontario's interim Provincial Water Quality Objective, which is 100 ppb (parts per billion).

Recovery wells have been in operation at the remediation site since the discovery of benzene in the soil in 2006.

The source of that leak is believed to be a discontinued benzene pipeline that had been emptied and taken out of service, according to Fisher.