Repairing Scotland’s £160M Glendoe hydro scheme will involve building 1.6km of drill and blast tunnel, it has emerged.
Owner Scottish and Southern Energy had earlier said that a single tunnel - thought to be around 200m long - would be needed to bypass a collapsed section of the headrace tunnel.
However, it has now admitted that this will be 900m long with an additional 700m long tunnel required for access to the damaged tunnel.
Bam Nuttall has been confirmed as the contractor carrying out the work - thought to be worth around £20M.
NCE understands that it will involve creating an appropriate entry point to the headrace tunnel and installation of a working platform within this tunnel to allow drill and blast plant to begin excavating the new bypass tunnel.
A source close to the project told NCE it was also possible that sprayed concrete would be needed to patch up cracks within the headrace as well as grout infilling work to block off the section where the collapse occurred.
The collapse happened 2km from the top of the 6.2km long headrace tunnel that carries water from the reservoir in the Monadhliath Mountains to the power house near the southern tip of Loch Ness.
Estimates have put the volume of the blockage at around 20,000t, but the cause of the dramatic rockfall is not yet known.
SSE is now hoping that work will be complete in time for it to begin operating the station again in summer 2011.
The 100MW plant has remained shut since the collapse happened just a few weeks after it was officially opened by the Queen in June last year. However, the 2011 target is already a revised date from the original 2010 re-start it hoped for.