Brian Walsh, an environmental scientist manager for the state Department of Environment and Natural Resources, said Wednesday the ditch in Marshall County appears to flow into a creek.
But Walsh says officials haven't spent significant resources following the ditch downstream because they know it's not contaminated.
Officials don't believe the leak polluted any surface water bodies or drinking water systems. A TransCanada spokeswoman said Tuesday the cause is unknown.
The company says that more than 16,000 gallons of oil had been removed as of Tuesday.