A jet fuel spill that happened over a week ago on Highway 401 is expected to take another four weeks to clean, the Ministry of Transportation says.

On Jan. 13, a tanker truck tipped over on the highway in Cambridge, spilling 50,000 litres of jet fuel onto the roadway.

"It's within our boundaries, our waterways, and our water supply wells," said Michael Gordon, the supervisor of environmental field services for the Region of Waterloo. "What we want is to ensure that those are safe."

According to the MTO, the contractor working to clean the spill found that the it was more extensive than initially thought.

The company estimates that the cleanup process will take about a month.

Most highway lanes in the affected area have reopened, but the Highway 6 North eastbound on-ramp is expected to stay close while cleaning efforts continue.

The Ministry of Environment, Conservation and Parks has been on-scene to review the process.

Containment booms have been employed in nearby creeks, and absorption pads were expected to be used to catch fuel travelling downstream.

Five wells near Shade’s Mills Creek have been closed as a precaution.