The coal tip which crashed down a Rhondda mountainside on the weekend was deemed to be a risk.
The leader of the local council who is dealing with the aftermath says they do not yet know how many similar sites there are in the county.
Andrew Morgan told ITV News millions of pounds will be spend dealing with the slip which will involve major engineering work, which is on top of the millions which are needed to repair flood damage elsewhere in the area.
He said the colliery tip at Tylorstown was a category D site at the "higher end" of the risk level, which determines how often the tip is inspected.
Records are now being checked to see where other tips are.
Geotechnical engineers have been at the site which is being constantly monitored with specialist radar equipment to see how much the mountain has - or is moving.
On Tuesday, the First Minister visited the site for himself and Rhondda Cynon Taff council say it is in discussions with the Welsh Government for financial help.
You can watch my report below:
There had been confusion over who was responsible for the land after the Coal Authority and Natural Resources Wales denied it was them.
Rhondda Cynon Taf Council later confirmed it was their responsibility.
The problem has been compounded by the flood at a data centre which has held records about the land.
Inspections are also taking place at other tip sites looking for cracks in the ground and other signs of movement.
The authorities say local people will be kept updated but there will be "no quick fix" to this problem.