The new Balloch education campus is now due to open in winter 2017.
In a report due to go before councillors, contractors discovered asbestos material under concrete foundations and hard standing following the demolition of the previous school.
The local authority said it was not possible to test under the foundation until the demolition phase and earlier investigations at the site found no asbestos.
-- Advertisement --
Specialist contractors have now prepared a remediation programme to remove the materials, which will add another three months to the construction programme and cost £900,000.
Councillors will be asked to approve the allocation of additional funding on Wednesday, 29 June.
The local authority's Strategic Director for Regeneration, Environment & Growth, Richard Cairns, said: "These are essential works which could not have been foreseen. We're now seeking council approval to allow the remediation to be carried out as quickly as possible and this would allow us to get to work on building this fantastic new facility for generations of young people."
(LM/MH)
