Firefighters sealed a drain after a small amount of an unknown hazardous substance was found on a road in Harpenden.
Hertfordshire Fire and Rescue were called were called to Westfield Road at 3.55pm after a blue puddle was identified next to an empty barrel with a hazard warning on it.
Firefighters sealed the drain to stop the substance entering the waterworks.
The Environment Agency are currently identifying the substance.
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