The Big Dig will NEVER be complete. There will be repairs galore, complete reconstructions of the most defective sections, and the inevitable expansions when the traffic gets unbearable again(if it is not already). You just can’t shut down such a huge cash cow for the pols, mob bosses, and union thugs. They will keep this thing going for hundreds of years, if possible.
To fix the leaks, why don't they use the old wooden boat-builder's fix? Sprinkle sawdust above the leaks. The sawdust expands and seals the leaks. Easy-peazy. :^)