There was a stone mason working at the site and I had an opportunity to visit with him about his work. The first task was to dry out the rock work, the re-mortar all the joints to keep the moisture out.
In the wheelbarrow is blocks of peat. You can see them layered on top of the walls to further protect the structure from water infiltration.
He's been working on the structure for a number of years and said he has another 4 or 5 before he retires...that is if his pension survives.