You are correct. I spent most of my life in the engineering field and been in charge of many large civil projects.
Boring 30 mile long twin 33 foot tunnels hundreds of feet below the Delta through peat soils will cost lives and the cost overruns will be enormous.
I suppose nothing these days is un-constructable if the agencies in charge have enough money. But this project comes closest to that reality as any I have ever seen.

Its very interesting. When dubious projects like the Brown Streak or Jerry’s Delta tunnels of love project meet the inevitable ferocious public opposition a curious phenomenon occurs.
The planners (or pipe dreamers, in this case) have a tendency to go underground as if that alone will quell public opposition.
Tunneling then becomes the way to get around rational arguments as to whether the project is economically feasible, constructable, or even makes any rational sense at all.

I rest my case.