A giant sinkhole that opened up in a residential street in St Albans, forcing the evacuation of 20 people, first appeared a week ago and injured a postman working on the street, Royal Mail said.
The 66ft (20m) crater spreads across the driveway and front garden of a property on Fontmell Close and is 33ft (10m) deep.
Twenty people from five homes were evacuated to Batchwood Leisure Centre shortly after 3am.
Royal Mail said the hazard first appeared on September 23 when a postman injured himself on a drain cover which gave way.
Hertfordshire County Council inspected the footpath but concluded there was "no reason to suspect that the hole would collapse".
Royal Mail spokeswoman Sally Hopkins said: "Royal Mail can confirm that one of our postmen was delivering in Fontmell Close last week (Wednesday September 23) when a drain cover gave way.
"We're happy to say that the postman was not seriously injured and we reported this incident to the council."
More than 50 properties are without gas and electricity, according to a fire service spokeswoman.
Hertfordshire County Council said: "We were informed about a hole in the footpath last week, it was inspected and barriers put around it on Wednesday 23 and work was scheduled to fill it in this morning.
"Following our inspection, there was no reason to suspect that the hole would collapse.
"Holes of this kind crop up across Hertfordshire often for historic reasons and we'd like to reassure the public that it is rare for them to turn into large holes."
The return to normal is likely to take weeks, the statement added.
It is the latest in a spate of sinkholes to open up across the UK in the last year.
In August a large hole reported to be 40ft deep appeared on a busy road in Manchester city centre.
Earlier in the year Traigh Golf Course, near Mallaig on Scotland's west coast, was left with £16,000 of damage after a hole appeared in part of the fairway.
In February last year another Hertfordshire garden collapsed as a 20ft-deep hole opened up in Croxley Green, near Watford.
In the same month a house in Ripon, North Yorkshire, was left close to collapse after a hole was found underneath it.