There’s a difference between a leaking pipe and a tunnel that is caving in.
The immediate problem seems to be that the tunnel lining is failing and restricting flow. From the article.
The risk right now is that the tunnel lining could continue to fail and, at some point, that might restrict our ability to get flow through it.
I believe the process I linked to could be a solution to the problem. At least for ten years or so until a new tunnel could be built.